Serum bilirubin is inversely associated with insulin resistance and metabolic syndrome among children and adolescents

Interactive effect of serum uric acid and total bilirubin for cardiovascular disease in Chinese patients with type 2 diabetes

Serum uric acid (SUA) at high levels and bilirubin at low levels were potent antioxidant but it was uncertain that whether SUA and total bilirubin (TBIL) had additive interaction for the risk of CVD in type 2 diabetes mellitus (T2DM). We conducted a cross-sectional survey of 6713 inpatients with T2DM and admitted to 81 tertiary care hospitals. CVD was defined as having either prior coronary heart disease or stroke or peripheral arterial disease. Binary logistic regression was used to estimate odds ratios of SUA and TBIL for CVD. The effect size of additive interaction was estimated by three measures, i.e., relative excess risk due to interaction, attributable proportion due to interaction and synergy index. Among 6713 patients with T2DM, 561 (8.36%) suffered from CVD. Using ≥283 umol/L (median) to define high SUA and <11.5 umol/L (n = 2290 or 34.11%) to define low TBIL, copresence of both factors (n = 621 or 9.25%) was associated with 5.18-fold (95% CI, 4.00–6.72) risk of CVD with significant additive interactions in multivariable analysis as compared to absence of both risk factors. The copresence of both high SUA and low TBIL was associated with a large increased risk of CVD in high-risk Chinese patients with type 2 diabetes.

Does bilirubin protect against developing diabetes mellitus?

After 25 years of evaluating bilirubin as a possible protective agent in neonatal and cardiovascular disease, interest has moved on to a exploring a possible protective role in diabetes mellitus (DM). This review finds conflicting prospective data for a protective relationship though there are retrospective, case-controlled data, that can only show association, which is not causality. Only prospective studies can show causality. Also, it would appear that the underlying biochemical assumptions do not readily translate from the animal to the human setting. Given that many factors impact on circulating bilirubin levels, it is not surprising that a clear-cut answer is not available; the jury is still out. Any relationship between DM and bilirubin might relate to intermediates in bilirubin metabolism, including relationships involving the genes for the enzymes participating in those steps. Nevertheless, the pursuit of bilirubin in disease causation is opening new avenues for research and if it is established that serum bilirubin can predict risks, much will have been achieved. The answer may have to come from molecular genetic analyses.

Biomarkers of Metabolic Syndrome: Biochemical Background and Clinical Significance

Biomarkers of the metabolic syndrome are divided into four subgroups. Although dividing them in groups has some limitations, it can be used to draw some conclusions. In a first part, the dyslipidemias and markers of oxidative stress are discussed, while inflammatory markers and cardiometabolic biomarkers are reviewed in a second part. For most of them, the biochemical background and clinical significance are discussed, although here also a well-cut separation cannot always be made. Altered levels cannot always be claimed as the cause, risk, or consequence of the syndrome. Several factors are interrelated to each other and act in a concerted, antagonistic, synergistic, or modulating way. Most important conclusions are summarized at the end of every reviewed subgroup. Genetic biomarkers or influences of various food components on concentration levels are not included in this review article.

Serum bilirubin levels are inversely associated with PAI-1 and fibrinogen in Korean subjects

OBJECTIVES

Oxidative stress may contribute to atherosclerosis and increased activation of the coagulation pathway. Bilirubin may reduce activation of the hemostatic system to inhibit oxidative stress, which would explain its cardioprotective properties shown in many epidemiological studies. This study investigated the association of serum bilirubin with fibrinogen and plasminogen activator inhibitor-1 (PAI-1), respectively.

METHODS

A cross-sectional analysis was performed on 968 subjects (mean age, 56.0 ± 11.2 years; 61.1% men) undergoing a general health checkup. Serum biochemistry was analyzed including bilirubin subtypes, insulin resistance (using homeostasis model of assessment [HOMA]), C-reactive protein (CRP), fibrinogen, and PAI-1.

RESULTS

Compared with subjects with a total bilirubin (TB) concentration of <10.0 μmol/L, those with a TB concentration of >17.1 μmol/L had a smaller waist circumference, a lower triglyceride level, a lower prevalence of metabolic syndrome, and decreased HOMA-IR and CRP levels. Correlation analysis revealed linear relationships of fibrinogen with TB and direct bilirubin (DB), whereas PAI-1 was correlated with DB. After adjustment for confounding factors, bilirubin levels were inversely associated with fibrinogen and PAI-1 levels, respectively. Multivariate regression models showed a negative linear relationship between all types of bilirubin and fibrinogen, whereas there was a significant linear relationship between PAI-1 and DB.

CONCLUSIONS

High bilirubin concentrations were independently associated with low levels of fibrinogen and PAI-1, respectively. The association between TB and PAI-1 was confined to the highest TB concentration category whereas DB showed a linear association with PAI-1. Bilirubin may protect against the development of atherothrombosis by reducing the hemostatic response.

Active and Passive Smoking and Serum Total Bilirubin in a Rural Korean Population

INTRODUCTION

Serum bilirubin is an endogenous antioxidant biomarker and its low level is a potential risk factor for smoking related health disorders. This study investigated the association of cigarette smoke with serum total bilirubin among Koreans.

METHODS

Between 2006 and 2011, we examined 4899 Korean adults living in a rural community. After excluding 38 participants with serum bilirubin more than 2mg/dL, 75 participants who did not report their smoking status or who had liver or bile duct disorders, and 711 participants with liver enzymes exceeding the upper reference values, we performed a cross-sectional analysis on 4075 participants. Participants were classified into four groups: never-smokers without secondhand smoke exposure (SHSE), never-smokers with SHSE, former smokers, and active smokers. Serum total bilirubin concentration was measured using the enzyme method.

RESULTS

Compared to never-smokers without SHSE, never-smokers with SHSE (β = -0.025 mg/dL), former smokers (β = -0.049 mg/dL), and active smokers (β = -0.149 mg/dL) had significantly lower serum bilirubin even after adjusting for demographic factors, study year, alanine aminotransferase, gamma-glutamyl transferase, hemoglobin, lifestyle factors, and chronic diseases. A sex-stratified analysis indicated that for men, former smokers and active smokers were significantly associated with having lower bilirubin when compared to never-smokers without SHSE. However, for women, never-smokers with SHSE and active smokers were significantly associated with having lower bilirubin when compared to never-smokers without SHSE.

CONCLUSION

Our findings suggest that both active and passive cigarette smoking are associated with low serum bilirubin among Korean adults.

IMPLICATIONS

Our results suggest that not only active smoking but also passive smoking including SHSE can have an influence on decreasing serum bilirubin levels. With this different point of view, our study supports efforts to create smoke-free environments in order to foster more favorable serum bilirubin profiles, which may improve endothelial function and reduce the risk of cardiovascular disease.

Serum bilirubin levels predict future development of metabolic syndrome in healthy middle-aged nonsmoking men

BACKGROUND

Despite epidemiologic research demonstrating an inverse relationship between serum bilirubin levels and the prevalence of metabolic syndrome, prospective data on serum bilirubin as a predictor of incident metabolic syndrome are limited.

METHODS

Serum bilirubin was examined as a risk marker for incident metabolic syndrome in a prospective study of 468 Taiwanese middle-aged men who were free of metabolic syndrome and other systemic diseases at baseline. These subjects were followed up in annual health examinations between 2001 and 2009 for the development of metabolic syndrome, which was defined according to unified criteria set by several major organizations.

RESULTS

Among the study subjects, 377 were nonsmokers and 91 were current smokers. All individuals were then stratified into 3 groups according to their baseline serum bilirubin levels (low, normal, and high). During a mean follow-up period of 7.58 years, 66 subjects developed metabolic syndrome. The incidence of metabolic syndrome was significantly reduced in the high-bilirubin group compared with the low-bilirubin group (6.4% vs 22.4%, P < .001). Multivariate Cox regression analysis revealed that the hazard ratio for incident metabolic syndrome between the highest and lowest tertiles of serum bilirubin levels was 0.246 (95% confidence interval 0.120-0.503). However, although it remained clearly evident in nonsmokers, the inverse correlation was attenuated in current smokers.

CONCLUSIONS

Increased serum bilirubin was associated with a reduced future risk of metabolic syndrome in apparently healthy middle-aged, nonsmoking men. Our findings support the predictive role of serum total bilirubin for future development of metabolic syndrome.

Haeme oxygenase signalling pathway: implications for cardiovascular disease

Evidence now points to the haeme oxygenase (HO) pathway as a possible actor in modulating risk for cardiovascular disease (CVD). In particular, the HO pathway may represent a key endogenous modulator of oxidative, inflammatory, and cytotoxic stress while also exhibiting vasoregulatory properties. In this review, we summarize the accumulating experimental and emerging clinical data indicating how activity of the HO pathway and its products may play a role in mechanisms underlying the development of CVD. We also identify gaps in the literature to date and suggest future directions for investigation. Because HO pathway activity can be influenced not only by genetic traits and environmental stimuli but also by a variety of existing pharmacologic interventions, the pathway could serve as a prime target for reducing the overall burden of CVD. Further work is needed to determine the role of HO pathway products as possible prognostic markers of risk for clinical CVD events and the extent to which therapeutic augmentation or inhibition of HO pathway activity could serve to modify CVD risk.

Circulating Markers of Liver Function and Cardiovascular Disease Risk

Measurement of serum concentrations of various liver enzymes and other nonenzymatic proteins and metabolites of heme metabolism (eg, bilirubin) is often undertaken in clinical practice. Measurement of these liver function tests is simple, quick, and relatively inexpensive. However, interpreting the liver function test results in patients without evidence of liver disease is often challenging. Concentrations of some of liver enzymes, such as γ-glutamyltransferase or alkaline phosphatase, and concentrations of liver-derived metabolites, such as bilirubin, may be influenced by metabolic processes beyond the liver, sometimes making interpretation of the test results difficult. This scenario frequently occurs both in individuals at risk of cardiovascular disease and in patients with known cardiovascular disease, often resulting in the clinicians ignoring the test results. In this brief review, we discuss the evidence for associations between key serum liver function tests and cardiovascular disease risk and where associations are robust; we provide an interpretation for possible mechanistic links between the liver function test and cardiovascular disease.

Prognostic impact of serum bilirubin level on long-term renal survival in IgA nephropathy

BACKGROUND

Serum bilirubin has been recognized as a novel endogenous antioxidant. The aim of our study was to evaluate the impact of serum bilirubin on kidney prognosis in IgA nephropathy (IgAN).

METHODS

We followed retrospectively 694 patients with IgAN diagnosed by renal biopsy between 1982 and 2010. The risk factors for developing end-stage renal disease (ESRD) were estimated using a Cox proportional hazard model. Predictive performance between models with or without serum bilirubin was evaluated by calculating the net reclassification improvement (NRI) and integrated discrimination improvement (IDI).

RESULTS

Seventy-seven patients developed ESRD during the median 4.9 years of follow-up. Estimated glomerular filtration rate, proteinuria and histological severity were inversely related to bilirubin levels. In multivariate analysis, serum bilirubin was an independent risk factor for ESRD (hazard ratio for every 0.1 mg/dL decrease in serum bilirubin, 1.18; 95 % CI, 1.04-1.33). The incidence rate of ESRD decreased linearly with the increases in bilirubin levels (P for trend <0.01). When bilirubin was incorporated into a model with conventional ESRD risk factors, the NRI and IDI were 0.281 (P = 0.02) and 0.019 (P = 0.01), respectively.

CONCLUSIONS

We demonstrated that lower bilirubin levels were significantly associated with higher risk of ESRD in IgAN. In addition, bilirubin provided incremental predictive value in the risk assessment for progression of IgAN beyond that provided by standard risk factors.

Bilirubin is independently associated with oxidized LDL levels in young obese patients

BACKGROUND

Bilirubin can prevent lipid oxidation in vitro, but the association in vivo with oxidized low-density lipoprotein (Ox-LDL) levels has been poorly explored. Our aim is to the association of Ox-LDL with total bilirubin (TB) levels and with variables related with metabolic syndrome and inflammation, in young obese individuals.

FINDINGS

125 obese patients (13.4 years; 53.6% females) were studied. TB, lipid profile including Ox-LDL, markers of glucose metabolism, and levels of C-reactive protein (CRP) and adiponectin were determined. Anthropometric data was also collected. In all patients, Ox-LDL correlated positively with BMI, total cholesterol, LDLc, triglycerides (TG), CRP, glucose, insulin and HOMAIR; while inversely with TB and HDLc/Total cholesterol ratio (P < 0.05 for all). In multiple linear regression analysis, LDLc, TG, HDLc and TB levels were significantly associated with Ox-LDL (standardized Beta: 0.656, 0.293, -0.283, -0.164, respectively; P < 0.01 for all). After removing TG and HDLc from the analysis, HOMAIR was included in the regression model. In this new model, LDLc remained the best predictor of Ox-LDL levels (β = 0.665, P < 0.001), followed by TB (β = -0.202, P = 0.002) and HOMAIR (β = 0.163, P = 0.010).

CONCLUSIONS

Lower bilirubin levels may contribute to increased LDL oxidation in obese children and adolescents, predisposing to increased cardiovascular risk.

Cross-sectional and longitudinal associations between serum bilirubin and dyslipidemia in a health screening population

OBJECTIVE

To investigate cross-sectional and longitudinal associations between serum total bilirubin (TB) and dyslipidemia.

METHODS

Odds ratios (ORs) of prevalent dyslipidemia for TB were calculated in 2113 men and 1265 women. Correlation coefficients between baseline TB as well as the change in TB over 5 years and baseline log triglycerides, baseline HDL cholesterol and the changes in log triglycerides and HDL cholesterol over 5 years were calculated. Hazard ratios (HRs) of incident hypertriglyceridemia and hypo-HDL cholesterolemia for TB over 5 years were calculated in 1324 men and 915 women and 1583 men and 884 women, respectively.

RESULTS

The ORs of prevalent hypertriglyceridemia and hypo-HDL cholesterolemia for each one SD increase in TB were 0.83 (p < 0.001) in men and 0.71 (p = 0.074) in women and 0.64 (p < 0.001) in men and 0.78 (p = 0.089) in women, respectively adjusted for age, smoking, and other confounders. The baseline TB was significantly correlated with baseline log triglycerides and HDL cholesterol both in men and women while the change in TB was significantly correlated with the changes in log triglycerides and HDL cholesterol in men and the change in HDL cholesterol in women. The HRs of incident hypertriglyceridemia and hypo-HDL cholesterolemia for each one SD increase in TB were 0.99 (p = 0.848) in men and 0.74 (p = 0.033) in women and 1.08 (p = 0.345) in men and 0.85 (p = 0.220) in women, respectively adjusted for age, smoking, and other confounders.

CONCLUSION

Baseline TB was significantly associated with both prevalent hypertriglyceridemia and hypo-HDL cholesterolemia in men and with incident hypertriglyceridemia in women.

Bilirubin, platelet activation and heart disease: a missing link to cardiovascular protection in Gilbert's syndrome?

Gilbert's syndrome (GS) is a relatively common condition, inducing a benign, non-hemolytic, unconjugated hyperbilirubinemia. Gilbert's Syndrome is associated with mutation in the Uridine Glucuronosyl Transferase 1A1 (UGT1A1) gene promoter, reducing UGT1A1 activity, which normally conjugates bilirubin allowing its elimination from the blood. Individuals with GS demonstrate mildly elevated plasma antioxidant capacity caused by elevated levels of unconjugated bilirubin (UCB), reduced thiols and glutathione. Interestingly, the development of, and risk of mortality from, cardiovascular disease is remarkably reduced in GS individuals. An explanation for this protection may be explained by bilirubin's ability to inhibit multiple processes that induce platelet hyper-reactivity and thrombosis, thus far under-appreciated in the literature. Reactive oxygen species are produced continuously via metabolic processes and have the potential to oxidatively modify proteins and lipids within cell membranes, which may encourage the development of thrombosis and CVDs. Oxidative stress induced platelet hyper-reactivity significantly increases the risk of thrombosis, which can potentially lead to tissue infarction. Here, we discuss the possible mechanisms by which increased antioxidant status might influence platelet function and link this to cardiovascular protection in GS. In summary, this is the first article to discuss the possible role of bilirubin as an anti-thrombotic agent, which inhibits platelet activation and potentially, organ infarction, which could contribute to the reduced mortality rate in mildly hyperbilirbinemic individuals.

Association of serum bilirubin and non-alcoholic fatty liver disease: A feasible therapeutic avenue?

AIM: To the look at the current strength of evidence and the potential application of anti-oxidants in this setting.

METHODS: Two electronic databases (PubMed and Web of Knowledge) were searched to January 2013 to find studies addressing serum bilirubin levels in non-alcoholic fatty liver disease (NAFLD). The search used key word combinations in relation to NAFLD and serum bilirubin specific to human adults only. After screening selected studies were reviewed in depth by two independent reviewers. Data synthesis with further meta-analysis was planned but not possible due to the heterogeneity of the outcome measures in these studies.

RESULTS: Out of 416 studies screened only seven studies were considered suitable for inclusion. All seven studies consistently reported an inverse association of bilirubin with NAFLD despite the heterogeneous sample of studies. Only two studies were prospective. No negative studies were found.

CONCLUSION: Most studies suggest a correlation between high bilirubin levels of any type are inversely correlated with NAFLD. But to date most of these studies have been poorly designed to allow meaningful conclusions, except one cohort study. There is a need for a large prospective cohort study in multiple populations to test this hypothesis fully before mechanistic associations can be established and therapeutic options of the apparent anti-oxidant effect of bilirubin be explored in NAFLD. Furthermore these studies should include analysis of UGT1A1 gene to expound upon underlying cause of unconjugated hyperbilirubinaemia.

Combined effects of smoking and bilirubin levels on the risk of lung cancer in Korea: the severance cohort study

BACKGROUND

Smoking is a major risk factor for lung cancer. Bilirubin, an antioxidant, is inversely associated with the risk of diseases related to oxidative stress. This study was conducted to determine the influence of smoking and bilirubin levels on the risk of lung cancer in the Severance cohort study.

METHODS

This study included 68,676 Korean who received a health examination at Severance Health Promotion Center from 1994 to 2004. Serum bilirubin measurements within normal range were divided into tertiles whereas smoking states were divided as never-smokers, former smokers and current smokers. A diagnosis of lung cancer was coded as occurring based on the report from the National Cancer Registry. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) were calculated using Cox proportional hazards model.

RESULTS

At the end of the study period, 240 patients (men: 181, women: 59) developed lung cancer. Compared to those with bilirubin levels ≥ 1.0 mg/dL, HRs (95% CI) for lung cancer were 2.8 (1.8-4.2) for subjects having bilirubin levels from 0.2 to 0.7 mg/dL in men. When we stratified our analysis by smoking status, bilirubin consistently showed a protective effect on the risk of lung cancer on both never- and current smokers. Current smokers having bilirubin levels from 0.2 to 0.7 mg/dL had a risk of lung cancer by 6.0-fold higher than never-smokers with bilirubin levels ≥ 1.0 mg/dL in men.

CONCLUSION

In this large prospective study, higher baseline bilirubin level in the normal range was associated with low risk of lung cancer. Smoking and low bilirubin levels were cumulatively associated with a higher risk of lung cancer.

Bilirubin is an independent factor inversely associated with glycated hemoglobin level in pediatric patients with type 1 diabetes

OBJECTIVE

Bilirubin is a potent antioxidant, and serum total bilirubin (STB) concentrations correlate negatively with cardiovascular risk. In adult diabetic patients and in healthy adults, a negative correlation between STB and glycated hemoglobin (HbA1c) has been reported. We investigated whether there is such an association in children and adolescents with type 1 diabetes mellitus.

METHODS

The study group included 224 patients with type 1 diabetes duration of more than 12 months. Patients with suspected or confirmed hemolytic anemia or liver dysfunction were excluded.

RESULTS

A statistically significant negative correlation was found between STB and HbA1c (R = -0.15; p = 0.024), which retained its significance in multivariate analysis (β = -0.18, p = 0.005). Patients' age and daily insulin dose were positively correlated with HbA1c levels, whereas other variables included in the multivariate analysis [sex, diabetes duration, insulin regimen, C-peptide, hemoglobin, mean corpuscular hemoglobin concentration (MCHC), alanine transaminase (ALT), and aspartate transaminase (AST)] did not correlate with HbA1c. The mean HbA1c level in patients with STB >1.2 mg/dL (>21 µmol/L; the threshold for clinical diagnosis of Gilbert's syndrome) was lower than in patients with STB ≤1.2 mg/dL (≤21 µmol/L), and the mean difference was 0.63% (6.9 mmol/mol; 95% CI: 0.11-1.16%).

CONCLUSIONS

These results show that in young patients with type 1 diabetes, STB concentration is an independent factor inversely associated with HbA1c level. Further studies should investigate the background and long-term effects of this association.

Serum total bilirubin concentrations are inversely associated with total white blood cell counts in an adult population

BACKGROUND

Several studies have shown that serum bilirubin has a protective effect against cardiovascular disease and that inflammation plays an important role in its pathogenesis. This cross-sectional study investigated whether there was an association between blood total white blood cell count, a simple indicator of inflammation, and serum total bilirubin concentration in a cohort of an adult population in Taiwan.

METHODS

A total of 2458 apparently healthy adults (1246 men and 1212 women) who attended health examination at a medical centre in central Taiwan were enrolled. We collected anthropometric measurements, fasting blood test results, lifestyle habits and medical history.

RESULTS

Total white blood cell counts decreased progressively when the concentrations of total bilirubin increased as demonstrated in the total bilirubin quartiles. Both total bilirubin concentrations and total white blood cell counts showed significant correlations with the components of metabolic syndrome, including triglyceride and high-density lipoprotein cholesterol concentrations. Multivariate linear regression analysis revealed that, for both genders, total bilirubin showed an independent negative correlation with total white blood cell count after adjusting for conventional cardiovascular risk factors.

CONCLUSIONS

Higher serum total bilirubin concentrations within the reference range were associated with lower blood total white blood cell counts, regardless of other classical cardiovascular risk factors.

Body fat percentage is a major determinant of total bilirubin independently of UGT1A1*28 polymorphism in young obese

Objectives

Bilirubin has potential antioxidant and anti-inflammatory properties. The UGT1A1*28 polymorphism (TA repeats in the promoter region) is a major determinant of bilirubin levels and recent evidence suggests that raised adiposity may also be a contributing factor. We aimed to study the interaction between UGT1A1 polymorphism, hematological and anthropometric variables with total bilirubin levels in young individuals.

Methods

350 obese (mean age of 11.6 years; 52% females) and 79 controls (mean age of 10.5 years; 59% females) were included. Total bilirubin and C-reactive protein (CRP) plasma levels, hemogram, anthropometric data and UGT1A1 polymorphism were determined. In a subgroup of 74 obese and 40 controls body composition was analyzed by dual-energy X-ray absorptiometry.

Results

The UGT1A1 genotype frequencies were 49.9%, 42.7% and 7.5% for 6/6, 6/7 and 7/7 genotypes, respectively. Patients with 7/7 genotype presented the highest total bilirubin levels, followed by 6/7 and 6/6 genotypes. Compared to controls, obese patients presented higher erythrocyte count, hematocrit, hemoglobin and CRP levels, but no differences in bilirubin or in UGT1A1 genotype distribution. Body fat percentage was inversely correlated with bilirubin in obese patients but not in controls. This inverse association was observed either in 6/7 or 6/6 genotype obese patients. UGT1A1 polymorphism and body fat percentage were the main factors affecting bilirubin levels within obese patients (linear regression analysis).

Conclusion

In obese children and adolescents, body fat composition and UGT1A1 polymorphism are independent determinants of total bilirubin levels. Obese individuals with 6/6 UGT1A1 genotype and higher body fat mass may benefit from a closer clinical follow-up.

Serum total bilirubin levels and prevalence of diabetic retinopathy in a Chinese population

BACKGROUND

Patients with type 2 diabetes (T2D) are at a high risk of developing microvascular complications, such as diabetic retinopathy (DR). Previous studies have shown that low serum bilirubin concentrations in T2D patients may increase the risk of diabetic complications. Thus, the aim of the present was to investigate the association between the prevalence of DR and serum concentrations of total bilirubin in a Chinese population.

METHODS

The present study was a population-based cross-sectional study on 1761 T2D patients aged ≥40 years from the Jiading district of Shanghai, China. Fundus photographs were taken to confirm the presence and severity of DR. Subjects were assigned to quartiles based on serum total bilirubin concentrations (Quartile (Q) 1 <0.60 mg/dL; Q2 0.60-0.76 mg/dL; Q3 0.77-0.99 mg/dL; Q4 >0.99 mg/dL). Logistic regression models were used to explore the association between bilirubin concentrations and the prevalence of DR.

RESULTS

The prevalence of DR in the entire study population was 9.6%. The prevalence of DR was significantly lower in Q4 compared with the other three quartiles (Ptrend  = 0.004). After adjustment for multiple confounding factors, T2D patients in Q4 (i.e. serum bilirubin >0.99 mg/dL) were less likely (odds ratio 0.55; 95% confidence interval 0.33-0.91) to suffer from DR than patients in Q1 (i.e. serum bilirubin <0.60 mg/dL).

CONCLUSION

Serum bilirubin concentrations were inversely associated with DR in an elderly Chinese population, independent of traditional risk factors for microvascular complications.

Effects of serum bilirubin on atherosclerotic processes

This review highlights the protective roles of bilirubin against the atherosclerotic process. Bilirubin belongs to the superfamily of tetrapyrrolic compounds formed during heme catabolism. Although for decades bilirubin was considered to be a harmful waste product, recent epidemiologic studies have shown that serum bilirubin levels have consistently been inversely associated with cardiovascular disease (CVD), as well as cardiovascular risk factors such as metabolic syndrome and diabetes. These clinical studies are supported by in vitro and in vivo experimental data and have demonstrated that bilirubin not only has an ability to scavenge overproduced reactive oxygen species and inhibit vascular smooth muscle cell proliferation but, additionally, has anti-inflammatory effects. In this review, we will discuss the inverse association of serum bilirubin and CVD and cardiovascular risk factors established in various clinical studies. We also review detailed experimental studies about the effect of bilirubin on atherosclerotic processes. In vitro, animal and human studies have proved that bilirubin inhibits oxidation of cholesterol which is an important step of atherosclerosis. Bilirubin attenuates chemotactic activity of monocytes and strongly inhibits adhesion of leukocytes to venule and production of pro-inflammatory cytokines. Bilirubin has inhibited serum-driven smooth muscle cell cycle progression at the G1 phase. Lastly, we will discuss briefly the influence of bilirubin on lipoprotein composition and endothelial dysfunction.

The relationship between total bilirubin levels and total mortality in older adults: the United States National Health and Nutrition Examination Survey (NHANES) 1999-2004

Objective

Due to its anti-oxidant and anti-inflammatory properties, bilirubin has been associated with reduced cardiovascular risk. A recent study demonstrated an L-shaped association of pre-treatment total bilirubin levels with total mortality in a statin-treated cohort. We therefore investigated the association of total bilirubin levels with total mortality in a nationally representative sample of older adults from the general population.

Methods

A total of 4,303 participants aged ≥60 years from the United States National Health and Nutrition Examination Survey 1999–2004 with mortality data followed up through December 31, 2006 were included in this analysis, with a mean follow-up period of 4.5 years.

Results

Participants with total bilirubin levels of 0.1–0.4 mg/dl had the highest mortality rate (19.8%). Compared with participants with total bilirubin levels of 0.5–0.7 mg/dl and in a multivariable regression model, a lower total bilirubin level of 0.1–0.4 mg/dl was associated with higher risk of total mortality (hazard ratios, 1.36; 95% confidence interval, 1.07–1.72; P = 0.012), while higher levels (≥0.8 mg/dl) also tended to be associated with higher risk of total mortality, but this did not reach statistical significance (hazard ratios, 1.24; 95% confidence interval, 0.98–1.56; P = 0.072).

Conclusion

In this nationally representative sample of older adults, the association of total bilirubin levels with total mortality was the highest among those with a level between 0.1 and 0.4 mg/dl. Further studies are needed to investigate whether higher total bilirubin levels could be associated with a higher mortality risk, compared to a level of 0.5–0.7 mg/dl.

Low serum bilirubin concentration is a novel risk factor for the development of albuminuria in patients with type 2 diabetes

OBJECTIVE

Bilirubin has been recognized as an important endogeneous antioxidant. Previous studies reported that bilirubin could prevent atherosclerosis. The aim of this study was to investigate if serum bilirubin concentration could be a predictor for the development of albuminuria in patients with type 2 diabetes.

MATERIALS AND METHODS

We measured serum bilirubin in 320 consecutive patients with normoalbuminuria. We performed follow-up study to assess the development of albuminuria, mean interval of which was 3.2±0.9years. Cox proportional hazards regression was used to examine the relationship between serum bilirubin concentration and the development of albuminuria.

RESULTS

During follow-up duration, 43 patients have developed albuminuria. In multivariate analysis, after adjusting for comprehensive risk factors, the risk of developing albuminuria was higher in the lowest quartile of serum bilirubin concentrations than that in the highest quartile of serum bilirubin concentrations (Hazard ratio, 5.76; 95% CI, 1.65 to 24.93).

CONCLUSIONS

Low serum bilirubin concentration could be a novel risk factor for the development of albuminuria in patients with type 2 diabetes.

Higher serum direct bilirubin levels were associated with a lower risk of incident chronic kidney disease in middle aged Korean men

Background

The association between serum bilirubin levels and incident chronic kidney disease (CKD) in the general population is unknown. We aimed to examine the association between serum bilirubin concentration (total, direct, and indirect) and the risk of incident CKD.

Methods and Findings

Longitudinal cohort study of 12,823 Korean male workers 30 to 59 years old without CKD or proteinuria at baseline participating in medical health checkup program in a large worksite. Study participants were followed for incident CKD from 2002 through 2011. Estimated glomerular filtration rate (eGFR) was estimated by using the CKD-EPI equation. CKD was defined as eGFR <60 mL/min per 1.73 m². Parametric Cox models and pooled logistic regression models were used to estimate adjusted hazard ratios for incident CKD. We observed 238 incident cases of CKD during 70,515.8 person-years of follow-up. In age-adjusted models, the hazard ratios for CKD comparing quartiles 2–4 vs. quartile 1 of serum direct bilirubin were 0.93 (95% CI 0.67–1.28), 0.88 (0.60–1.27) and 0.60 (0.42–0.88), respectively. In multivariable models, the adjusted hazard ratio for CKD comparing the highest to the lowest quartile of serum direct bilirubin levels was 0.60 (95% CI 0.41–0.87; P trend = 0.01). Neither serum total nor indirect bilirubin levels were significantly associated with the incidence of CKD.

Conclusions

Higher serum direct bilirubin levels were significantly associated with a lower risk of developing CKD, even adjusting for a variety of cardiometabolic parameters. Further research is needed to elucidate the mechanisms underlying this association and to establish the role of serum direct bilirubin as a marker for CKD risk.

Higher serum bilirubin level as a protective factor for the development of diabetes in healthy Korean men: a 4 year retrospective longitudinal study

OBJECTIVE

Bilirubin, a natural product of heme catabolism by heme oxygenase, one of key antioxidant enzymes, has been recognized as a substance with potent antioxidant and cytoprotective properties. Several studies have shown a significant negative relationship between serum bilirubin levels and the risk of metabolic disorders, including type 2 diabetes. However, longitudinal studies investigating the association of elevated serum bilirubin levels and type 2 diabetes are lacking. In the present study, we aimed to investigate the longitudinal effects of baseline serum bilirubin concentrations on the development of type 2 diabetes in healthy Korean men.

MATERIALS AND METHODS

This 4 year retrospective longitudinal observational study was conducted at the Asan Medical Center, Seoul, Republic of Korea. The study population consisted of 5960 men without type 2 diabetes who underwent routine health examinations in 2007 (baseline) and 2011 (follow-up). Baseline serum bilirubin concentrations were determined by the vanadate oxidation method.

RESULTS

During a 4 year period, 409 incident cases of diabetes (6.9 %) were identified. Incident type 2 diabetes decreased across the baseline bilirubin quartile categories (P for trend <0.001). In multivariable-adjusted model, the relative risk (RR) for the development of type 2 diabetes was significantly lower in the highest (i.e., 1.30-2.00 mg/dl) than in the lowest bilirubin quartile category (i.e., ≤ 0.90 mg/dl), even after adjustment for confounding variables (RR=0.69, 95% confidence interval 0.48-0.99, P for trend = 0.041).

CONCLUSIONS

The results indicate that serum total bilirubin level may provide additional information for predicting future development of type 2 diabetes in healthy subjects.

Relation of conjugated bilirubin concentrations to the presence of coronary artery calcium

Whether conjugated bilirubin concentration, resulting from hepatic UDP-glucuronosyltransferase 1 A1 activity, is associated with cardiovascular disease is unknown. Our aim was to investigate the relation between serum conjugated bilirubin concentrations and coronary artery calcium score (CACS) as a measure of preclinical atherosclerosis. Data were analyzed from an occupational cohort of 14,583 subjects who underwent a cardiac computed tomographic estimation of CACS and measurements of risk factors. Logistic regression was used to describe associations between bilirubin concentrations and CACS. The proportion of subjects with a CACS >0 (total: men = 1,351, women = 111) decreased across increasing conjugated bilirubin quartiles (men p <0.001, women p = 0.005). After adjustment for age, gender, waist, systolic blood pressure, smoking, exercise, alcohol, homeostatic model assessment of insulin resistance, glucose, triglyceride, high- and low-density lipoprotein cholesterols, high-sensitivity C-reactive protein, lipoprotein (a), ferritin, fatty liver, cerebrovascular accident, coronary artery disease, hypertension, and diabetes, there was an inverse independent association between conjugated bilirubin and CACS >0 (odds ratio 0.76, 95% confidence interval 0.64 to 0.92, p = 0.004, for top vs bottom quartile). After further adjustment for estimated glomerular filtration rate, the odds ratio was 0.83 (95% confidence interval 0.69 to 0.99), p = 0.04. Exclusion of subjects with a high bilirubin (total >1.3 mg/dl) did not attenuate the association. In conclusion, there was a strong inverse and independent relation between conjugated bilirubin and CACS. The mechanism behind this association is not clear and may not be causal, but the effects of glucuronidation on cardiovascular disease risk should be tested.

Non-alcoholic fatty liver disease: factors associated with its presence and onset

Non-alcoholic fatty liver disease (NAFLD) may progress to cirrhosis, liver failure, and complicated hepatocellular carcinoma. In addition, NAFLD is a risk factor for the development of other serious diseases, such as diabetes or cardiovascular disease. Therefore, the detection of early-stage NAFLD is important. Many studies have described the factors that predict the presence of NAFLD and its onset, and several markers have been identified. These markers have enabled the identification of high-risk patients and have improved routine medical practice. To prevent advanced disease, clinicians need to have simple markers that predict the onset of NAFLD so that interventions can be started at much earlier stages of disease. This review summarizes the current state of knowledge regarding independent factors, as reported in large studies, that predict the presence of NAFLD and its onset, especially markers that can be used in daily medical practice, such as physical measurements and blood tests.

High sensitive C-reactive protein and serum amyloid A are inversely related to serum bilirubin: effect-modification by metabolic syndrome

BACKGROUND

Bilirubin has been implicated in cardiovascular protection by virtue of its anti-inflammatory and anti-oxidative properties. The metabolic syndrome is featured by enhanced low-grade systemic inflammation and oxidative stress. Serum amyloid A (SAA) impairs anti-oxidative properties of high-density lipoprotein (HDL). We determined relationships of high sensitive C-reactive protein (hs-CRP) and SAA with bilirubin in subjects with and without metabolic syndrome (MetS).

METHODS

Serum total bilirubin, hs-CRP, SAA and homeostasis model assessment- insulin resistance (HOMA-IR) were documented in 94 subjects with and in 73 subjects without MetS (26 and 54 subjects with type 2 diabetes mellitus (T2DM), respectively).

RESULTS

Bilirubin was lower in MetS (P = 0.013), coinciding with higher hs-CRP (P < 0.001) and SAA levels (P = 0.002). In all subjects combined, hs-CRP was inversely related to bilirubin (r = -0.203, P = 0.008), irrespective of the presence of MetS or T2DM (interaction terms: P ≥ 0.75). The inverse relationship of bilirubin with SAA was confined to subjects without MetS (r = -0.267, P = 0.009). Furthermore, the presence of either MetS or T2DM modified the relationship of bilirubin with SAA (interaction terms: β = 0.366, P = 0.003 and β = 0.289, P = 0.025, respectively) in age- and sex-adjusted analyses. Effect modification was also found for HOMA-IR (β = 0.790, P = 0.020). Of the individual MetS components, the strongest interaction of bilirubin on SAA was observed with low HDL cholesterol (β = 0.435, P < 0.001).

CONCLUSIONS

hs-CRP is inversely related to bilirubin, suggesting that low bilirubin is implicated in enhanced low-grade systemic inflammation. The inverse relationship of SAA with bilirubin was found to be absent in MetS, which could be attributable to MetS-associated abnormalities in HDL characteristics.

Hepatic function and the cardiometabolic syndrome

Despite skeletal muscle being considered by many as the source of insulin resistance, physiology tells us that the liver is a central and cardinal regulator of glucose homeostasis. This is sometimes underestimated because, in contrast with muscle, investigations of liver function are technically very difficult. Nevertheless, recent experimental and clinical research has demonstrated clearly that, due in part to its anatomic position, the liver is exquisitely sensitive to insulin and other hormonal and neural factors, either by direct intrahepatic mechanisms or indirectly by organ cross-talk with muscle or adipose tissue. Because the liver receives absorbed nutrients, these have a direct impact on liver function, whether via a caloric excess or via the nature of food components (eg, fructose, many lipids, and trans fatty acids). An emerging observation with a possibly great future is the increase in intestinal permeability observed as a consequence of high fat intake or bacterial modifications in microbiota, whereby substances normally not crossing the gut gain access to the liver, where inflammation, oxidative stress, and lipid accumulation leads to fatty liver, a situation observed very early in the development of diabetes. The visceral adipose tissue located nearby is another main source of inflammatory substances and oxidative stress, and also acts on hepatocytes and Kupffer cells, resulting in stimulation of macrophages. Liberation of these substances, in particular triglycerides and inflammation factors, into the circulation leads to ectopic fat deposition and vascular damage. Therefore, the liver is directly involved in the development of the prediabetic cardiometabolic syndrome. Treatments are mainly metformin, and possibly statins and vitamin D. A very promising avenue is treatment of the leaky gut, which appears increasingly to be an important causal factor in hepatic insulin resistance and steatosis.

Serum bilirubin level is inversely associated with nonalcoholic steatohepatitis in children

OBJECTIVES

Oxidative stress has been implicated in the development of nonalcoholic fatty liver disease (NAFLD) and progression to the more severe form, nonalcoholic steatohepatitis (NASH), in children. We aimed to study the clinical correlation between bilirubin, a potent endogenous antioxidant with cytoprotective properties, and histopathological findings in pediatric patients with NAFLD.

METHODS

We included consecutive children with biopsy-proven NAFLD and obtained demographic, clinical, and histopathological data. We performed logistic regression analysis to assess the clinical factors associated with the histological features of NASH or fibrosis.

RESULTS

From a total of 302 biopsies, 67% (203) had evidence of NASH, whereas 64.2% had some degree of fibrosis (stage 1 in 51%, stage 2 in 6.3%, and stage 3 in 6.6%). Mean total bilirubin was significantly lower in the NASH group compared with the non-NASH group (0.65 ± 0.24 vs 0.73 ± 0.22 mg/dL, P = 0.007). Higher total bilirubin levels were negatively correlated with the presence of steatosis and the NAFLD activity score (P < 0.05), whereas a trend in that direction was observed for presence of fibrosis and inflammation (P = 0.051). On multivariable analysis, higher bilirubin levels were significantly associated with a decreased likelihood of a histological diagnosis of NASH on biopsy (odds ratio 0.29, 95% CI 0.10-0.85, P = 0.024).

CONCLUSIONS

In children with NAFLD, there is an inverse relation between serum bilirubin levels and the presence of NASH on biopsy. This may be secondary to the antioxidant effect of bilirubin.

Serum bilirubin levels are lower in overweight asymptomatic middle-aged adults: an early indicator of metabolic syndrome?

OBJECTIVE

Low levels of bilirubin have recently been associated with obesity, diabetes mellitus, and metabolic syndrome. Here, we hypothesized that serum bilirubin levels might be already altered in overweight asymptomatic middle-aged individuals before full development of the metabolic syndrome.

METHODS

Healthy nonsmoking adults aged 25-49 (64 women and 32 men) participated in this cross-sectional study. All participants who reported stable weight within the last three months underwent standard anthropomorphological measurements of body composition, blood pressure measurements, aerobic and anaerobic capabilities assessment, dietary intake evaluation, and fasting serological measurements of total and direct bilirubin, glucose, insulin, triglycerides, total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and C-reactive protein. Participants were divided into normal-weight and overweight groups. Linear correlation and multiple regression analyses were used to examine the association of serum bilirubin levels with all metabolic syndrome risk factor changes.

RESULTS

Serum bilirubin levels were lower in overweight healthy individuals of both sexes, and were negatively associated with abdominal obesity, insulin resistance, fasting glucose, fasting insulin, fasting triglycerides, total cholesterol, low-density lipoprotein cholesterol, and C-reactive protein levels but positively associated with aerobic body capabilities.

CONCLUSION

Our findings suggest that serum bilirubin levels have the potential to be employed as an early biomarker for indicating asymptomatic individuals at increased risk of developing metabolic syndrome.

Total bilirubin is inversely associated with metabolic syndrome but not a risk factor for metabolic syndrome in Japanese men and women

Serum total bilirubin (TB) is a potent antioxidant and inversely associated with metabolic syndrome (MetS) in Asian populations. However, there has been no study which is aimed to investigate whether TB is a risk factor for MetS or not. We investigated cross-sectional and longitudinal associations between TB and MetS in 2,435 Japanese men and 1,436 Japanese women. The odds ratios [95 % confidence interval (CI)] of coexisting MetS for each 1 SD increase in log TB were 0.850 (0.754-0.958) (p = 0.008) in men and 0.809 (0.656-0.998) (p = 0.047) in women adjusted for sex, age, smoking, and other confounding covariates. Those for the third and fourth quartiles of TB compared with the lowest quartile were 0.720 (0.537-0.965) (p = 0.028) and 0.737 (0.530-1.052) (p = 0.095), respectively, in men and 0.822 (0.473-1.427) (p = 0.486) and 0.704 (0.362-1.369) (p = 0.301), respectively, in women. There was a tendency that TB and MetS changed inversely to each other. The similarly adjusted hazard ratios of developing MetS for each 1 SD increase in log TB and for the higher quartiles of TB compared with the lowest quartile were not significant either in men or in women. TB is inversely associated with MetS but not a risk factor for MetS in Japanese men and women.

High serum total bilirubin as a protective factor against hip bone loss in healthy middle-aged men

Bilirubin is known to have a physiologic role as an antioxidant that efficiently scavenges peroxyl radicals and suppresses oxidation, and oxidative stress has detrimental effects on bone metabolism. In the present study, we performed a 3-year longitudinal study of healthy middle-aged men, investigating the association between serum total bilirubin concentrations and annualized changes in bone mineral density (BMD). The study enrolled a total of 917 Korean men aged 40 years or older who had undergone comprehensive routine health examinations with an average follow-up interval of 3 years. BMD at proximal femur sites was measured with dual-energy X-ray absorptiometry using the same equipment at baseline and follow-up. The overall mean annualized rates of bone loss at the total femur, femoral neck, and trochanter were -0.25 %/year, -0.34 %/year, and -0.44 %/year, respectively. After adjustment for potential confounders, the rates of bone loss at all proximal femur sites were significantly attenuated in a dose-response fashion across increasing bilirubin concentrations (P = 0.006-0.046). Moreover, compared to subjects in the lowest bilirubin quartile category, those in the highest bilirubin quartile category showed significantly less bone loss at all proximal femur sites after adjustment for confounding factors (P = 0.010-0.048). This study provides the first clinical evidence that serum total bilirubin could be a protective marker against future bone loss, especially in subjects without liver diseases.

The relationship between DXA-based and anthropometric measures of visceral fat and morbidity in women

Background

Excess accumulation of visceral fat is a prominent risk factor for cardiovascular and metabolic morbidity. While computed tomography (CT) is the gold standard to measure visceral adiposity, this is often not possible for large studies - thus valid, but less expensive and intrusive proxy measures of visceral fat are required such as dual-energy X-ray absorptiometry (DXA). Study aims were to a) identify a valid DXA-based measure of visceral adipose tissue (VAT), b) estimate VAT heritability and c) assess visceral fat association with morbidity in relation to body fat distribution.

Methods

A validation sample of 54 females measured for detailed body fat composition - assessed using CT, DXA and anthropometry – was used to evaluate previously published predictive models of CT-measured visceral fat. Based upon a validated model, we realised an out-of-sample estimate of abdominal VAT area for a study sample of 3457 female volunteer twins and estimated VAT area heritability using a classical twin study design. Regression and residuals analyses were used to assess the relationship between adiposity and morbidity.

Results

Published models applied to the validation sample explained >80% of the variance in CT-measured visceral fat. While CT visceral fat was best estimated using a linear regression for waist circumference, CT body cavity area and total abdominal fat (R² = 0.91), anthropometric measures alone predicted VAT almost equally well (CT body cavity area and waist circumference, R² = 0.86). Narrow sense VAT area heritability for the study sample was estimated to be 58% (95% CI: 51-66%) with a shared familial component of 24% (17-30%). VAT area is strongly associated with type 2 diabetes (T2D), hypertension (HT), subclinical atherosclerosis and liver function tests. In particular, VAT area is associated with T2D, HT and liver function (alanine transaminase) independent of DXA total abdominal fat and body mass index (BMI).

Conclusions

DXA and anthropometric measures can be utilised to derive estimates of visceral fat as a reliable alternative to CT. Visceral fat is heritable and appears to mediate the association between body adiposity and morbidity. This observation is consistent with hypotheses that suggest excess visceral adiposity is causally related to cardiovascular and metabolic disease.

Genetically elevated bilirubin and risk of ischaemic heart disease: three Mendelian randomization studies and a meta-analysis

BACKGROUND

Elevated plasma levels of bilirubin, an endogenous antioxidant, have been associated with reduced risk of ischaemic heart disease (IHD) and myocardial infarction (MI). Whether this is a causal relationship remains unclear.

OBJECTIVE

We tested the hypothesis that elevated plasma bilirubin is causally related to decreased risk of IHD and MI.

DESIGN

We used a Mendelian randomization approach and three independent studies from Copenhagen, Denmark. We measured bilirubin in 43 708 white individuals from the general population, and genotyped rs6742078 G>T in the uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene in 67 068 individuals, of whom 11 686 had IHD.

RESULTS

Third versus first tertile of baseline bilirubin levels was associated with 134% increased bilirubin levels, with sex- and age-adjusted hazard ratios (HRs) of 0.86 [95% confidence interval (CI), 0.76-0.98; P = 0.02] for IHD and 0.81 (95% CI, 0.66-0.99; P = 0.04) for MI, but with corresponding multifactorially adjusted HRs of 0.93 (95% CI, 0.82-1.06; P = 0.29) and 0.90 (95% CI, 0.73-1.12; P = 0.35). UGT1A1 rs6742078 TT versus GG genotype was associated with 95% increased bilirubin levels (P < 0.001); TT versus GG genotype was associated with odds ratios (ORs) of 1.03 (95% CI, 0.96-1.11; P = 0.73) for IHD and 1.01 (95% CI, 0.92-1.12; P = 0.68) for MI. Finally, in a meta-analysis of the present three studies and eight previous studies including a total of 14 711 cases and 60 324 controls, the random effects OR for ischaemic cardiovascular disease for genotypes with approximately 100% increased bilirubin levels versus reference genotypes was 1.01 (95% CI, 0.88-1.16).

CONCLUSION

These data suggest that plasma bilirubin is not causally associated with risk of IHD.

Relationships between serum total bilirubin levels and metabolic syndrome in Korean adults

BACKGROUND AND AIMS

Metabolic syndrome (MS) is associated with insulin resistance in all parts of its natural history, which is accompanied by oxidative stress. Bilirubin is a potent endogenous antioxidant and cytoprotectant. The current study was performed to identify the major predictors of the total bilirubin level and to assess the relationships between the total bilirubin levels and MS in Korean adults.

METHODS AND RESULTS

This is a cross-sectional study involving 12342 adults aged 20 years and over who visited a Health Promotion Center. Physical examinations and laboratory tests including total and direct bilirubin levels were performed. MS was defined based on the modified NCEP-ATP III definition and the determinations of the Korean Society for the Study of Obesity. The results showed that hemoglobin had the strongest influence on the total bilirubin levels after adjusting for age, gender, and all other variables. The high-bilirubin group (≥15.4 μmol/L in males and ≥12.1 μmol/L in females) was associated with significantly decreased odds of MS compared to the low-bilirubin group (OR 0.74 [95% CI 0.64-0.86]). High levels of bilirubin also were negatively associated with abdominal obesity and hypertriglyceridemia. The total bilirubin levels decreased with an increase in the number of MS components after adjustment for all covariates.

CONCLUSION

Within the physiological range, the serum total bilirubin level was negatively associated with the MS in subjects without overt metabolic or cardiovascular diseases. This may be partially due to the negative association between the total bilirubin level and abdominal obesity and hypertriglyceridemia.

Serum bilirubin levels are inversely associated with nonalcoholic fatty liver disease

Background/Aims

Serum bilirubin exerts antioxidant and cytoprotective effects. In addition, elevated serum bilirubin levels are associated with a decreased risk of metabolic and cardiovascular diseases. However, few studies have evaluated whether serum bilirubin is associated with non-alcoholic fatty liver disease (NAFLD), which is closely associated with other metabolic diseases. The aim of this study was thus to elucidate the association between serum total bilirubin levels and NAFLD.

Methods

A cross-sectional study of 17,348 subjects undergoing a routine health check-up was conducted. Subjects positive for hepatitis B or hepatitis C virus, or with other hepatitis history were excluded. NAFLD was diagnosed on the basis of typical ultrasonographic findings and an alcohol consumption of less than 20 g/day.

Results

The mean age of the subjects was 49 years and 9,076 (52.3%) were men. The prevalence of NAFLD decreased steadily as the serum bilirubin level increased in both men and women (P<0.001 for both). Multivariate regression analysis adjusted for other metabolic risk factors showed that serum bilirubin level was inversely associated with the prevalence of NAFLD [odds ratio (OR)=0.88, 95% confidence interval (CI)=0.80-0.97]. Furthermore, there was an inverse, dose-dependent association between NAFLD and serum total bilirubin levels (OR=0.83, 95% CI=0.75-0.93 in the third quartile; OR=0.80, 95% CI=0.71-0.90 in the fourth quartile vs. lowest quartile, P for trend <0.001).

Conclusions

Serum bilirubin levels were found to be inversely associated with the prevalence of NAFLD independent of known metabolic risk factors. Serum bilirubin might be a protective marker for NAFLD.

The prevalence of metabolic syndrome in children: a systematic review of the literature

BACKGROUND

Metabolic syndrome has been identified as a condition of childhood relatively recently. The aim in this study was to describe the prevalence of metabolic syndrome in children allowing for differences in metabolic syndrome definitions.

METHODS

This was a systematic review of the OVID, EMBASE, and CINAHL databases, capturing details of overall prevalence and prevalence within groups categorized by obesity, gender, age, and ethnicity.

RESULTS

In all, 378 studies published since 2003 were identified, and of these 85 papers were included in the present review. When all studies were considered, the median prevalence of metabolic syndrome in whole populations was 3.3% (range 0%-19.2%), in overweight children was 11.9% (range 2.8%-29.3%), and in obese populations was 29.2% (range 10%-66%). Within-study analyses confirmed higher prevalence for obese compared to overweight (P=0.012) and obese compared to nonobese, nonoverweight children (P<0.001). Within-study analyses also revealed higher median metabolic syndrome prevalence for boys compared to girls (5.1% versus 3.0%, P<0.001) and also in older compared with younger children (5.6% versus 2.9%, P=0.001). Limited evidence was found to suggest differences between ethnic groups, and there were insufficient studies to determine whether metabolic syndrome prevalence was increasing over time.

CONCLUSIONS

This is the first systematic review of all of the relevant literature. It describes the magnitude of associations between metabolic syndrome and obesity, age, and gender. We find evidence that ethnicity and geography may be important to metabolic syndrome prevalence in children and these associations require further study.

A cohort study of serum bilirubin levels and incident non-alcoholic fatty liver disease in middle aged Korean workers

Background

Serum bilirubin may have potent antioxidant and cytoprotective effects. Serum bilirubin levels are inversely associated with several cardiovascular and metabolic endpoints, but their association with nonalcoholic fatty liver disease (NAFLD) has not been investigated except for a single cross-sectional study in a pediatric population. We assessed the prospective association between serum bilirubin concentrations (total, direct, and indirect) and the risk for NAFLD.

Methods and Findings

We performed a cohort study in 5,900 Korean men, 30 to 59 years of age, with no evidence of liver disease and no major risk factors for liver disease at baseline. Study participants were followed in annual or biennial health examinations between 2002 and 2009. The presence of fatty liver was determined at each visit by ultrasonography. We observed 1,938 incident cases of NAFLD during 28,101.8 person-years of follow-up. Increasing levels of serum direct bilirubin were progressively associated with a decreasing incidence of NAFLD. In age-adjusted models, the hazard ratio for NAFLD comparing the highest to the lowest quartile of serum direct bilirubin levels was 0.61 (95% CI 0.54–0.68). The association persisted after adjusting for multiple metabolic parameters (hazard ratio comparing the highest to the lowest quartile 0.86, 95% CI 0.76–0.98; P trend = 0.039). Neither serum total nor indirect bilirubin levels were significantly associated with the incidence of NAFLD.

Conclusions

In this large prospective study, higher serum direct bilirubin levels were significantly associated with a lower risk of developing NAFLD, even adjusting for a variety of metabolic parameters. Further research is needed to elucidate the mechanisms underlying this association and to establish the role of serum direct bilirubin as a marker for NAFLD risk.

The role of bilirubin in diabetes, metabolic syndrome, and cardiovascular diseases

Bilirubin belongs to a phylogenetically old superfamily of tetrapyrrolic compounds, which have multiple biological functions. Although for decades bilirubin was believed to be only a waste product of the heme catabolic pathway at best, and a potentially toxic compound at worst; recent data has convincingly demonstrated that mildly elevated serum bilirubin levels are strongly associated with a lower prevalence of oxidative stress-mediated diseases. Indeed, serum bilirubin has been consistently shown to be negatively correlated to cardiovascular diseases (CVD), as well as to CVD-related diseases and risk factors such as arterial hypertension, diabetes mellitus, metabolic syndrome, and obesity. In addition, the clinical data are strongly supported by evidence arising from both in vitro and in vivo experimental studies. This data not only shows the protective effects of bilirubin per se; but additionally, of other products of the heme catabolic pathway such as biliverdin and carbon monoxide, as well as its key enzymes (heme oxygenase and biliverdin reductase); thus, further underlining the biological impacts of this pathway. In this review, detailed information on the experimental and clinical evidence between the heme catabolic pathway and CVD, and those related diseases such as diabetes, metabolic syndrome, and obesity is provided. All of these pathological conditions represent an important threat to human civilization, being the major killers in developed countries, with a steadily increasing prevalence. Thus, it is extremely important to search for novel markers of these diseases, as well as for novel therapeutic modalities to reverse this unfavorable situation. The heme catabolic pathway seems to fulfill the criteria for both diagnostic purposes as well as for potential therapeutical interventions.

Cigarette smoking and serum bilirubin subtypes in healthy Korean men: the Korea Medical Institute study

OBJECTIVES

Cigarette smoking is a modifiable risk factor for cardiovascular disease. Bilirubin is a potent antioxidant and its concentration decreases in smokers. However, studies about the association between cigarette smoking and bilirubin are scarce and most are limited to total bilirubin. Additionally, bilirubin is highly related to hemoglobin. Therefore, this study evaluates the association between bilirubin subtypes and cigarette smoking in healthy Korean men independently of hemoglobin.

METHODS

This study included 48 040 Korean men aged 30 to 87 years who visited the Korea Medical Institute for routine health examinations from January to December, 2007. The association of smoking with total, direct, and indirect bilirubin was assessed by logistic regression analysis taking into consideration differences in subjects and smoking characteristics.

RESULTS

Current smokers had lower bilirubin concentrations than never-smokers and ex-smokers. Smoking amount and duration were inversely significantly associated with total, direct, and indirect bilirubin. In a multivariable adjusted model, compared to never-smokers, the odds ratios (ORs) and 95% confidence intervals (CIs) of current smokers with the highest number of pack-years were 1.7 (1.6 to 1.9) for total, 1.5 (1.4 to 1.6) for direct, and 1.7 (1.6 to 1.9) for indirect bilirubin. After further adjustment for hemoglobin, this association became stronger (OR [95% CI], 2.1 [1.9 to 2.2] for total; 1.9 [1.8 to 2.0] for direct; 2.0 [1.9 to 2.2] for indirect bilirubin).

CONCLUSIONS

In this study, bilirubin subtypes are inversely associated with smoking status, smoking amount, and smoking duration in healthy Korean men independently of hemoglobin. Further studies are needed to investigate this association in healthy Korean women.

Characterization of the effect of serum bilirubin concentrations on coronary endothelial function via measurement of high-sensitivity C-reactive protein and high-density lipoprotein cholesterol

Bilirubin can prevent oxidation of low-density lipoprotein (LDL) and may protect against atherosclerosis and coronary heart disease (CHD). The goal of this study was to characterize the relationship between bilirubin and CHD through measurements of bilirubin concentration, coronary endothelial function, and markers of oxidative stress, inflammation, and lipid/glucose metabolism. The study population consisted of 141 patients without CHD who underwent Doppler flow study. Vascular reactivity was examined by intracoronary administration of papaverine, acetylcholine (ACh) and nitroglycerin using a Doppler guide wire. Serum bilirubin, high-sensitivity C-reactive protein (hsCRP), malondialdehyde-modified LDL, LDL cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), fasting plasma glucose (FPG), and immunoreactive insulin were also measured. Homeostasis model assessment insulin resistance index and estimated glomerular filtration rate (eGFR) were calculated. Univariate analysis revealed that both percent change in coronary blood flow (CBF) and coronary artery diameter induced by ACh correlated positively with log-transformed bilirubin (r = 0.22, P < 0.05; r = 0.20, P < 0.05, respectively). Percent change in CBF in response to ACh correlated positively with eGFR (r = 0.24, P < 0.05) and correlated inversely with age, LDL-C, and log-transformed FPG (r = -0.24, P < 0.05; r = -0.17, P < 0.05, r = -0.22, P < 0.05, respectively). Multivariate analysis revealed that log-transformed bilirubin was the only independent predictor of percent change in CBF in response to ACh. Multivariate analysis revealed that log-transformed hsCRP and HDL-C were independent predictors of log-transformed bilirubin. These results suggest that a high level of bilirubin is associated with favorable coronary endothelial function, which may be mediated via the effect of bilirubin on inflammation and HDL-C.

Low serum total bilirubin concentrations are associated with increased prevalence of metabolic syndrome in Chinese

BACKGROUND

To investigate the association between serum concentrations of total bilirubin (TBil) in the physiological range and metabolic syndrome (MS) in middle-aged and elderly Chinese, as well as any associations between serum TBil concentrations and insulin resistance, hyperinsulinemia, and systemic inflammation.

METHODS

A cross-sectional study was conducted on 1423 individuals recruited from an urban community of Shanghai (average age 62.3 years) to investigate the relationship between bilirubin and cardiovascular diseases. Metabolic syndrome was defined according to the National Cholesterol Education Program Adult Treatment Panel III criteria for Asian Americans.

RESULTS

Total bilirubin concentrations were significantly lower in individuals with MS compared with those without (0.65 ± 0.21 vs 0.69 ± 0.22 mg/dL, respectively; P=0.002). The adjusted mean concentration of TBil decreased gradually with an increase in the number of components of MS (P(trend) < 0.0001). After adjustment for a range of potential confounders (e.g. age, sex, body mass index, smoking, alcohol intake, homeostasis model assessment of insulin resistance etc.), each 1 SD increase in TBil was found to be associated with a 17% reduction in the risk of MS (odds ratio 0.83; 95% confidence interval 0.73-0.95; P=0.006). Furthermore, after adjustment for all covariables, each 1 SD increase in TBil was found to be associated with lower odds of central obesity, hypertriglyceridemia, low high-density lipoprotein-cholesterol, and hyperglycemia. Serum TBil concentrations were inversely associated with hyperinsulinemia, insulin resistance, and systemic inflammation.

CONCLUSIONS

Serum TBil concentrations within the physiological range were inversely associated with MS and insulin resistance, hyperinsulinemia, and systemic inflammation in middle-aged and elderly Chinese.

Relationship between bilirubin and C-reactive protein

BACKGROUND

Epidemiologic studies have shown that serum total bilirubin is inversely related to an increased risk of coronary artery disease. However, the number of studies which have focused on the relationship between bilirubin and C-reactive protein (CRP), which is a marker reflecting chronic vascular inflammation, are limited.

METHOD

This cross-sectional study consisted of 2307 Korean adults who visited the Center for Health Promotion for a routine health check-up from January 2009 to December 2009.

RESULT

CRP level showed a declining tendency as total bilirubin increased according to total bilirubin quartiles. Negative relations of CRP with both total and direct bilirubin were found after adjustment of age, body mass index, hypertension, diabetes, hypercholesterolemia, cardiovascular disease, taking aspirin, smoking, alcohol drinking and regular exercise and total bilirubin or direct bilirubin.

CONCLUSIONS

This study found that elevation of the two types of bilirubin (total and direct) have a relationship with a low serum CRP level among apparently healthy Korean adults. It is hypothesized that a low serum CRP level may be due to the antioxidant and anti-inflammatory effects of bilirubin metabolism.