Obesity paradox and mortality in adults with and without incident type 2 diabetes: a matched population-level cohort study

Racial and Ethnic Disparities in Primary Prevention of Cardiovascular Disease

Cardiovascular disease (CVD) disproportionately affects ethnic-minority groups globally. Ethnic-minority groups face particularly high CVD burden and mortality, exacerbated by disparities across modifiable risk factors, wider determinants of health, and limited access to preventative interventions. This narrative review summarizes evidence on modifiable risk factors, such as physical activity, hypertension, diet, smoking, alcohol consumption, diabetes, and the polypill for the primary prevention of CVD in ethnic minorities. Across these factors, we find inequities in risk factor prevalence. The evidence underscores that inequalities in accessibility to interventions and treatments impede progress in reducing CVD risk using primary prevention interventions for ethnic-minority people. Although culturally tailored interventions show promise, further research is required across the different risk factors. Social determinants of health and structural inequities also exacerbate CVD risk for ethnic-minority people and warrant greater attention. Additionally, we find that only limited ethnicity-specific data and guidelines are available on CVD primary prevention interventions for most risk factors. To address these gaps in research, we provide recommendations that include the following: investigating the sustainability and real-world effectiveness of culturally sensitive interventions; ensuring that ethnic-minority peoples' perspectives are considered in research; longitudinal tracking of risk factors; interventions and outcomes in ethnic-minority people; and ensuring that data collection and reporting of ethnicity data are standardized.

Body mass index and risk of all-cause mortality among elderly Chinese: An empirical cohort study based on CLHLS data

The aim of our study was to evaluate the relationship between body mass index (BMI) and all-cause mortality among elderly Chinese. The subjects of our study were a cohort of 13 319 elderly Chinese enrolled between 2008 and 2018. Participants were classified in three groups: underweight (<18.5 kg/m²), normal weight (18.5-24.9 kg/m²), overweight and obese (≥25 kg/m²) according to different BMI levels. Cox proportional-hazards regression model was used to analyze the association between BMI grouping and the risk of mortality among the three groups and each corresponding subgroup. The restricted cubic spline regression was performed to investigate the variation tendency of BMI and mortality in different groups and subgroups. We found that the hazard ratios (HRs) of mortality in the underweight and the normal-weight groups were 1.213 and 1.104, respectively, compared with those in the overweight and obesity groups. HR for mortality decreased as BMI increased, although this phenomenon was not observed as not a linear relationship in all participants. Nonetheless, this nonlinear relationship was significant in type 2 diabetes patients. Among subjects with non-type 2 diabetes, the shape of the negative curve, reflecting the HR for BMI and mortality, decreased when BMI increased. Our findings suggest that an obesity paradox exists in non-type 2 diabetes patients, in which BMI has a nonlinear negative relationship with mortality. Conversely, in type 2 diabetes patients there is a U-shaped association. Obesity may thus be protective for all-cause mortality among non-diabetic older populations.

Association of body indices and risk of mortality in patients with type 2 diabetes

INTRODUCTION

A body shape index (ABSI) is independently associated with mortality in general population, but studies on the predictability of ABSI in the risk of mortality in patients with type 2 diabetes (T2D) are limited. We aimed to examine the independent and joint association of ABSI, body mass index (BMI), waist circumference (WC), waist-to-hip ratio (WHR), waist-to-height ratio (WHtR), and body roundness index (BRI) with mortality in patients with T2D.

RESEARCH DESIGN AND METHODS

The study included 11 872 patients (46.5% women) aged 30 years and older and who took part in diabetes care management program of a medical center in Taiwan. Body indices were evaluated by anthropometric measurements at baseline between 2001 and 2016, and their death status was followed up through 2021. Multivariate Cox regression models were used to assess the effect of body indices on mortality.

RESULTS

During a mean follow-up of 10.2 years, 560 cardiovascular disease (CVD) deaths and 3043 deaths were recorded. For ABSI, WC, WHR, WHtR and BRI, all-cause mortality rates were statistically significantly greater in Q4 versus Q2. For BMI and WHtR, all-cause mortality rates were also statistically significantly greater in Q1 versus Q2. The combination of BMI and ABSI exhibited a superiority in identifying risks of all-cause mortality and CVD mortality (HRs: 1.45 and 1.37, both p<0.01).

CONCLUSIONS

Combined use of ABSI and BMI can contribute to the significant explanation of the variation in death risk in comparison with the independent use of BMI or other indices.

A phenome-wide comparative analysis of genetic discordance between obesity and type 2 diabetes

Obesity and type 2 diabetes are causally related, yet there is considerable heterogeneity in the consequences of both conditions and the mechanisms of action are poorly defined. Here we show a genetic-driven approach defining two obesity profiles that convey highly concordant and discordant diabetogenic effects. We annotate and then compare association signals for these profiles across clinical and molecular phenotypic layers. Key differences are identified in a wide range of traits, including cardiovascular mortality, fat distribution, liver metabolism, blood pressure, specific lipid fractions and blood levels of proteins involved in extracellular matrix remodelling. We find marginal differences in abundance of Bacteroidetes and Firmicutes bacteria in the gut. Instrumental analyses reveal prominent causal roles for waist-to-hip ratio, blood pressure and cholesterol content of high-density lipoprotein particles in the development of diabetes in obesity. We prioritize 17 genes from the discordant signature that convey protection against type 2 diabetes in obesity, which may represent logical targets for precision medicine approaches.

Body mass index versus surrogate measures of central adiposity as independent predictors of mortality in type 2 diabetes

BACKGROUND

An "obesity paradox" for mortality has been shown in chronic disorders such as diabetes, and attributed to methodological bias, including the use of body mass index (BMI) for obesity definition. This analysis investigated the independent association of BMI versus surrogate measures of central adiposity with all-cause mortality in individuals with type 2 diabetes.

METHODS

The Renal Insufficiency And Cardiovascular Events Italian Multicentre Study is a prospective cohort study that enrolled 15,773 patients in 19 Italian centres in 2006-2008. Exposures were BMI and the surrogate measures of central adiposity waist circumference (WC), waist-to-height ratio (WHtR), and A Body Shape Index (ABSI). Vital status was retrieved on 31 October 2015 for 15,656 patients (99.3%), RESULTS: Age- and sex-adjusted hazard ratios and 95% confidence intervals were significantly higher in BMI-based underweight (1.729 [1.193-2.505), P = 0.004), moderately obese (1.214 [1.058-1.392), P = 0.006) and severely obese (1.703 [1.402-2.068), P < 0.0001), lower in overweight (0.842 [0.775-0.915), P < 0.0001) and similar in mildly obese (0.950 [0.864-1.045), P = 0.292), compared to normal-weight individuals. When further adjusting for smoking, physical activity (PA), and comorbidities, risk was lower also in mildly obese versus normal-weight patients. The BMI-mortality relationship did not change after sequentially excluding ever smokers, individuals with comorbidities, and those died within two years from enrollment and when analyzing separately participants below and above the median age. Conversely, a paradox relationship was observed among inactive/moderately inactive, but not moderately/highly active patients. Mortality risk adjusted for age, gender, smoking, PA and comorbidities was significantly higher in the highest tertile of WC (1.279 [1.089-1.501], P = 0.003), WHtR (1.372 [1.165-1.615], P < 0.0001), and ABSI (1.263 [1.067-1.495], P = 0.007) versus the lowest tertile. However, risk was lower in the intermediate versus lowest tertile for WC (0.823 [0.693-0.979], P = 0.028), similar for WHtR, and higher, though not significantly, for ABSI.

CONCLUSIONS

An "overweight paradox" remained after controlling for age, smoking, and comorbidities, arguing against a collider bias or reverse causation. However, it could be partly explained by confounding from PA level, possibly through its impact on lean mass and cardiorespiratory fitness. No obesity paradox was observed with WHtR and especially ABSI, which predicted mortality risk associated with central adiposity better than WC. Trial registration ClinicalTrials.gov, NCT00715481, 15 July, 2008.

Body mass index and cancer mortality in patients with incident type 2 diabetes: A population-based study of adults in England

AIMS

We evaluated the relationship between body mass index (BMI) and cancer mortality in incident type 2 diabetes.

METHODS

We used the Clinical Practice Research Datalink GOLD (1998-2015), linked with the Office of National Statistics mortalities, and derived an incident type 2 diabetes cohort (N = 176 886; aged 30-85 years). We determined BMI ±12 months diabetes diagnosis. The primary outcome was cancer mortality, categorized into deaths from obesity-related cancers (ORCs) and non-ORCs. Secondary outcomes were site-specific cancer mortality and main causes of deaths [cancer, cardiovascular disease (CVD), non-cancer non-CVD]. We developed gender-specific Cox models and expressed risk as hazard ratios and 95% confidence intervals, stratified by smoking status.

RESULTS

With 886 850 person-years follow-up, 7593 cancer deaths occurred. Among women who never smoked, there were positive associations between BMI and deaths from endometrial (hazard ratios per 5 kg/m² : 1.43; 95% confidence interval 1.26-1.61). Among men, associations between BMI and ORC mortality were inverse but attenuated towards null among never smokers and excluding deaths in the first 2 years. In men, the proportion of CVD deaths increased from 36.8% in BMI category 22.5 to 24.9 kg/m² to 43.6% in BMI category ≥40 kg/m² (p < .001).

CONCLUSIONS

We found some relationships between BMI and cancer mortality in patients with type 2 diabetes, but interpretations need to account for smoking status, reverse causality and deaths from CVD.

Weight Changes in Type 2 Diabetes and Cancer Risk: A Latent Class Trajectory Model Study

INTRODUCTION

Body mass index (BMI) is often elevated at type 2 diabetes (T2D) diagnosis. Using latent class trajectory modelling (LCTM) of BMI, we examined whether weight loss after diagnosis influenced cancer incidence and all-cause mortality.

METHODS

From 1995 to 2010, we identified 7,708 patients with T2D from the Salford Integrated Record database (UK) and linked to the cancer registry for information on obesity-related cancer (ORC), non-ORC; and all-cause mortality. Repeated BMIs were used to construct sex-specific latent class trajectories. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox regression models.

RESULTS

Four sex-specific BMI classes were identified; stable-overweight, stable-obese, obese-slightly-decreasing, and obese-steeply-decreasing; comprising 41%, 45%, 13%, and 1% of women, and 45%, 37%, 17%, and 1% of men, respectively. In women, the stable-obese class had similar ORC risks as the obese-slightly-decreasing class, whereas the stable-overweight class had lower risks. In men, the obese-slightly-decreasing class had higher risks of ORC (HR = 1.86, 95% CI: 1.05-3.32) than the stable-obese class, while the stable-overweight class had similar risks No associations were observed for non-ORC. Compared to the stable-obese class, women (HR = 1.60, 95% CI: 0.99-2.58) and men (HR = 2.37, 95% CI: 1.66-3.39) in the obese-slightly-decreasing class had elevated mortality. No associations were observed for the stable-overweight classes.

CONCLUSION

Patients who lost weight after T2D diagnosis had higher risks for ORC (in men) and higher all-cause mortality (both genders) than patients with stable obesity.

Inverse association between body mass index and all-cause mortality in rural chinese adults: 15-year follow-up of the Anqing cohort study

OBJECTIVE

To investigate the association between body mass index (BMI) and all-cause mortality in a Chinese rural population.

DESIGN

Prospective cohort study.

SETTING

This study was conducted from 2003 to 2018 in Anqing, Anhui Province, China.

PARTICIPANTS

17 851 participants aged 25-64 years (49.4% female) attending physical examinations and questionnaire were included in this study. The inclusion criterion was families having a minimum of three participating siblings. The exclusion criteria included participants without family number and BMI data at baseline.

OUTCOME MEASURES

The outcome measure was all-cause mortality. Generalized estimating equation (GEE) regression analysis was performed to determine the association between baseline BMI and all-cause mortality.

RESULTS

During a mean follow-up period of 14.1 years, 730 deaths (8.0%) occurred among men, and 321 deaths (3.6%) occurred among women. The mean BMI for males was 21.3[Formula: see text] kg/m², and for female it was 22.1±3.1 kg/m². Baseline BMI was significantly inversely associated with all-cause mortality risk for per SD increase (OR, 0.79 (95% CI, 0.72 to 0.87) for males; OR, 0.88 (95% CI, 0.76 to 1.01) for females). When BMI was stratified with cut points at 20 and 24 kg/m², compared with the low BMI group, a significantly lower risk of death was found in the high BMI group (BMI ≥24: OR, 0.57 (95% CI, 0.43 to 0.77) in males; 0.65 (95% CI, 0.46 to 0.93) in females) after adjustment for relevant factors.

CONCLUSIONS

In this relatively lean rural Chinese population, the risk of all-cause mortality decreased with increasing BMI. The excess risk of all-cause mortality associated with a high BMI was not seen among this rural population.

The obesity paradox and diabetes

BACKGROUND

Obesity has been proven to be a risk factor for type 2 diabetes mellitus (T2DM) through numerous pathogenetic mechanisms. Unexpectedly, some studies suggest that subjects with overweight/obesity and T2DM have better clinical outcome than their normal weight peers. This finding is described as "obesity paradox" and calls into question the importance of weight loss in this specific population.

OBJECTIVE

This article is a narrative overview on the obesity and type 2 diabetes mellitus, particularly regarding the obesity paradox in T2DM patients.

METHODS

We used as sources MEDLINE/PubMed, CINAHL, EMBASE, and Cochrane Library, from inception to March 2020; we chose 30 relevant papers regarding the association of obesity with clinical outcome and mortality of patients affected by T2DM.

RESULTS

Many studies report that in patients with T2DM, overweight and obesity are associated with a better prognosis than underweight or normal weight, suggesting the presence of an obesity paradox. However, these studies have numerous limitations due to their mainly retrospective nature and to numerous confounding factors, such as associated pathologies, antidiabetic treatments, smoking habit, lack of data about distribution of body fat or weight history.

CONCLUSION

Literature data regarding the phenomenon of obesity paradox in T2DM patients are controversial due to the several limitations of the studies; therefore in the management of patients with overweight/obesity and T2DM is recommended referring to the established guidelines, which indicate diet and physical activity as the cornerstone of the treatment.

LEVEL OF EVIDENCE

Level V: narrative review.

Effective SLOPE: EffectS of Lifestyle interventions in Older PEople with obesity: a systematic review and network meta-analysis protocol

INTRODUCTION

Obesity is highly prevalent in older adults aged 65 years or older. Different lifestyle interventions (diet, exercise, self-management) are available but benefits and harms have not been fully quantified comparing all available health promotion interventions. Special consideration must be given to functional outcomes and possible adverse effects (loss of muscle and bone mass, hypoglycaemia) of weight loss interventions in this age group. The objective of this study is to synthesise the evidence regarding the effects of different types and modalities of lifestyle interventions, or their combinations, on physical function and obesity-related outcomes such as body composition in older adults with obesity.

METHODS AND ANALYSES

Six databases (Medline, Embase, Cochrane Central Register of Controlled Trials, Cumulated Index to Nursing and Allied Health Literature (CINAHL), Psychinfo and Web of Science) and two trial registries (Clinicaltrials.gov and the WHO International Clinical Trials Registry Platform) will be searched for randomised controlled trials of lifestyle interventions in older adults with obesity. Screening (title/abstract and full-text) and data extraction of references as well as assessment of risk of bias and rating of the certainty of evidence (Grading of Recommendations, Assessment, Development and Evaluation for network meta-analyses) will be performed by two reviewers independently. Frequentist random-effects network meta-analyses will be conducted to determine the pooled effects from each intervention.

ETHICS AND DISSEMINATION

We will submit our findings to peer-reviewed journals and present at national and international conferences as well as in scientific medical societies. Patient-targeted dissemination will involve local and national advocate groups.

PROSPERO REGISTRATION NUMBER

CRD42019147286.

Relationship Between Body Mass Index, Antidiabetic Agents, and Midterm Mortality in Patients With Both Type 2 Diabetes Mellitus and Acute Coronary Syndrome

Background

The aim of this study was to determine the influence of various antidiabetic therapies on the relationship between body mass index and all‐cause mortality in patients with diabetes mellitus and acute coronary syndrome.

Methods and Results

This was a prospective, observational study comprising 1193 patients diagnosed with type 2 diabetes mellitus and acute coronary syndrome. The patients were stratified into 4 body mass index categories, and their mortality rates were compared using time‐dependent Cox regression analysis using normal weight (body mass index, 18.5–23.9) as the reference. Subsequently, the influence of antidiabetic therapies on the association between BMI and mortality were analyzed. Seventy‐four patients (6.2%) died over 2 years of follow‐up. The mortality rate was lowest in the class I obese group (3.35%) and highest in the normal‐weight group (9.67%). After adjusting for covariates, class I obesity paradoxically remained significantly protective against mortality compared with normal weight (hazard ratio, 0.141; P=0.049); interaction term analysis showed that insulin therapy influenced this “obesity paradox” (P=0.045). When the patients were stratified by insulin use, the protective effect of obesity disappeared in the insulin‐treated patients but persisted in the non–insulin‐treated patients.

Conclusions

In patients with type 2 diabetes mellitus and acute coronary syndrome, the relationship between body mass index and mortality rate is U‐shaped, with class I obesity representing the nadir and normal weight the peak. The protective effect of obesity disappeared in patients treated with insulin.

Body mass index and mortality among middle-aged Japanese individuals with diagnosed diabetes: The Japan Public Health Center-based prospective study (JPHC study)

AIM

To examine the association between body mass index (BMI) and mortality among middle-aged people with diabetes in Japan.

METHODS

A total of 3032 men and 1615 women, aged 40-69 years, with diabetes were analyzed. Cox proportional hazards models, adjusted for potential confounding factors, were used to estimate mortality hazard ratios (HRs) across BMI categories at the baseline.

RESULTS

There were 1761 deaths during a mean follow-up period of 18.5 years. Increased all-cause mortality was observed at both ends of the BMI distribution; compared with the reference BMI category (23.0-24.9 kg/m²), the HRs were 1.25 (95% confidence interval [CI], 0.9997-1.56) in the lowest (14.0-18.9 kg/m²) and 1.36 (95% CI, 1.06-1.74) in the highest (30.0-39.9 kg/m²) categories (P = 0.001). Similar all-cause mortality trends were observed after excluding deaths within 3 years of follow-up, as well as for men and men who had ever smoked. While a similar non-linear pattern was observed for cancer-specific mortality, heart disease-specific mortality was only increased in the highest BMI category (HR, 1.86; 95% CI, 1.06-3.25).

CONCLUSION

This population-based prospective study demonstrated increased all-cause mortality at both ends of the BMI distribution among Japanese people with diabetes.

Obesity, smoking habits, and serum phosphate levels predicts mortality after life-style intervention

Background

Life-style interventions, including smoking cessation and weight control are of importance for managing future escalating prevalence of obesity. Smoking habits and obesity have jointly great impact on mortality, however mechanisms behind the effect and variables involved in the obesity paradox is still unknown.

Objectives

This study examines risk factors for all-cause, cardiovascular, and cancer mortality in males and females with high cardiovascular risk, mediated by smoking habits, body mass index (BMI, kg/m²), and serum phosphate (S-P) levels.

Methods

Patients were admitted to the Vindeln Patient Education Center in groups of 30 for a four-week residential comprehensive program (114 hours) focusing on smoking cessation, stress reduction, food preferences and selections, and physical exercise. The follow-up, in years from 1984 to 2014 corresponds to 30 years. This study included 2,504 patients (1,408 females and 1,096 males). Cox regression analysis was used to assess mortality risk associated with smoking habits, low and high BMI, and low and high S-P levels.

Results

High BMI (>34,2 kg/m²), current smoking, type 2 diabetes mellitus (T2DM), high serum calcium (S-Ca), mmol/L and high systolic blood pressure (SBP, mmHg) were associated with all-cause mortality irrespective of sex. Former and current smoking females had a high all-cause mortality (adjusted hazard ratio [HR] 1.581; 95% CI 1.108–2.256, adjusted hazard ratio [HR] 1.935; 95% CI 1.461–2.562, respectively) while current smoking and high BMI increased risk for cardiovascular mortality (adjusted hazard ratio [HR] 3.505; 95% CI 2.140–5.740 and [HR] 1.536; 95% CI 1.058–2.231, respectively). Neither low nor high levels of S-P predicted all-cause, cardiovascular disease (CVD) and cancer mortality in males or females while low levels of S-P predicted all-cause mortality in smokers (adjusted hazard ratio [HR] 1.713; 95% CI 1.211–2.424). In non-smokers, low BMI (<27.6 kg/m²) was protecting and high BMI a risk for all-cause mortality. In males, ischemic heart disease (IHD), and low serum albumin (S-Alb) were associated with all-cause mortality. In females, an interaction between high BMI and smoking (HbmiSM) decreased the cardiovascular mortality (adjusted hazard ratio [HR] 0.410; 95% CI 0.179–0.937, respectively).

Conclusions

High BMI and current smoking were associated with all-cause mortality in both males and females in the present high cardiovascular-risk cohort. In current smokers and non-smokers, T2DM and high S-Ca were associated with an increase in all-cause mortality, while low S-P was associated with all-cause mortality in smokers. Interaction between high BMI and smoking contribute to the obesity paradox by being protective for cardiovascular mortality in females.

An in-depth analysis of glycosylated haemoglobin level, body mass index and left ventricular diastolic dysfunction in patients with type 2 diabetes

BACKGROUND

Glycosylated hemoglobin (HbA1c) has a detrimental impact on the myocardium with left ventricular (LV) diastolic dysfunction. Obesity is a risk factor of type 2 diabetes. To understand the relationships between HbA1c, body mass index (BMI) and LV diastolic dysfunction, we performed this interaction analysis in patients with type 2 diabetes.

METHODS

Total 925 type 2 diabetes patients were selected from the patients who were diagnosed and treated at the First Affiliated Hospital of Shenzhen University. Patients' BMI levels were defined as normal (BMI < 24 kg/m²) and overweight /obese (BMI ≥ 24 kg/m²). Patients' HbA1c levels were grouped as HbA1c ≥ 9%、7% ≤ HbA1c < 9% and HbA1c < 7%. Logistic regression, stratified, interaction analysis, multivariate Cox regression and curve fitting analysis were performed to investigate the correlations and interactions between HbA1c and BMI with LV diastolic dysfunction.

RESULTS

The BMI levels were significantly associated with LV diastolic dysfunction in the patients with type 2 diabetes [adjusted model: 1.12 (1.05, 1.20), P = 0.001]. While HbA1c levels had association with LV diastolic dysfunction only in normal BMI group patients [adjusted model: 1.14 (1.01, 1.30), P = 0.0394] and curve correlation was observed. There was a significant interaction between BMI and HbA1c to affect LV diastolic dysfunction (P = 0.0335). Cox regression model analysis showed that the risk of LV diastolic dysfunction was a U type correlation with HbA1c levels in the normal weight group and the turning point was HbA1c at 10%. HbA1c level was not found to have a significant association with LV diastolic dysfunction in overweight/obese group.

CONCLUSIONS

In patients with type 2 diabetes, correlation between LV diastolic dysfunction and HbA1c was interactively affected by BMI. Glycemic control is beneficial to the heart function in normal body weight patients. For overweight/obese patients, the risk of LV diastolic dysfunction was not determined by the HbA1c level, indicating it may be affected by other confounding factors.

The Importance of Body Composition in Explaining the Overweight Paradox in Cancer-Counterpoint

Despite a greater risk of cancer associated with higher BMI, overweight (BMI 25-<30 kg/m²) and class I obese (BMI 30-<35 kg/m²) patients often have a paradoxically lower risk of overall mortality after a cancer diagnosis, a phenomenon called the "obesity paradox." Only when patients exceed a BMI ≥35 kg/m² are elevations in mortality risk consistently noted. This paradox has been dismissed as the result of methodologic bias, which we will describe and debate here. However, even if such bias influences associations, there is growing evidence that body composition may in part explain the paradox. This phenomenon may more accurately be described as a BMI paradox. That is, BMI is a poor proxy for adiposity and does not distinguish muscle from adipose tissue, nor describe adipose tissue distribution. Low muscle mass is associated with higher risk of recurrence, overall and cancer-specific mortality, surgical complications, and treatment-related toxicities. Patients with who are overweight or obese have on average higher levels of muscle than their normal-weight counterparts. Also, there is some evidence that patients with moderate levels of subcutaneous adipose tissue may have lower mortality. More research utilizing body composition is needed to clarify the effects of adiposity on cancer mortality. Cancer Res; 78(8); 1906-12. ©2018 AACR.

Exploring the association between BMI and mortality in Australian women and men with and without diabetes: the AusDiab study

AIMS/HYPOTHESIS

There is conflicting evidence about the obesity paradox-the counterintuitive survival advantage of obesity among certain subpopulations of individuals with chronic conditions. It is believed that results supporting the obesity paradox are due to methodological flaws, such as collider bias. The aim of this study was to examine the association between obesity and mortality in Australian men and women. In addition, we explored whether obesity would appear to be protective if the analysis was restricted to a subpopulation with disease, and to discuss the potential role of collider bias in producing such a result.

METHODS

The examined cohort included 10,575 Australian adults (4844 men and 5731 women) aged 25-91 years who were recruited for the AusDiab baseline survey in 1999 and followed-up through 2014. The main predictor variable was BMI categorised as normal weight (18.5 to <25 kg/m²), overweight (25 to <30 kg/m²) and obese (≥30 kg/m²), and the outcome of interest was all-cause mortality. Hazard ratios were estimated from Cox proportional hazards regression models in the entire cohort and then in subpopulations with and without diabetes.

RESULTS

A total of 1477 deaths occurred during 145,384 person-years (median 14.6 years) of follow-up. Mortality was higher in obese than in normal-weight individuals for the full population (HR 1.18; 95% CI 1.05, 1.32). When an interaction between diabetes status and BMI category was added to the model, there was no evidence of an interaction between BMI and diabetes status (p = 0.92). When participants with and without diabetes were analysed separately, there was no evidence of an association between obesity and mortality in those with diabetes (HR 0.91; 95% CI 0.62, 1.33).

CONCLUSIONS/INTERPRETATION

In the entire AusDiab cohort, we found a significantly higher mortality among obese participants as compared with their normal-weight counterparts. We found no difference in the obesity-mortality association between individuals with and without diabetes.

“Obesity paradoxes”: main causes of an “inverse” cardiovascular epidemiology

Taken the continuous increase of obesity prevalence, most countries in the world deal with an epidemy, one of the main healthcare concerns. In the structure of nosology associated with overweight and obesity, cardiovascular is leading. Also, in the recent trials and meta analyses there is negative correlation found for body mass index and clinical outcomes characterizing better survival and lower events rate in those with higher BMI, as less chronic diseases. Such facts facilitated a number of discussions on the predictive value of overweight and obesity and consideration whether to correct those in cardiovascular patients as secondary prevention. Current article is focused on the main causes for an “inverse” cardiovascular epidemiology in overweight and obesity.

Adiposity-Mortality Relationships in Type 2 Diabetes, Coronary Heart Disease, and Cancer Subgroups in the UK Biobank, and Their Modification by Smoking

OBJECTIVE

The obesity paradox in which overweight/obesity is associated with mortality benefits is believed to be explained by confounding and reverse causality rather than by a genuine clinical benefit of excess body weight. We aimed to gain deeper insights into the paradox through analyzing mortality relationships with several adiposity measures; assessing subgroups with type 2 diabetes, with coronary heart disease (CHD), with cancer, and by smoking status; and adjusting for several confounders.

RESEARCH DESIGN AND METHODS

We studied the general UK Biobank population (N = 502,631) along with three subgroups of people with type 2 diabetes (n = 23,842), CHD (n = 24,268), and cancer (n = 45,790) at baseline. A range of adiposity exposures were considered, including BMI (continuous and categorical), waist circumference, body fat percentage, and waist-to-hip ratio, and the outcome was all-cause mortality. We used Cox regression models adjusted for age, smoking status, deprivation index, education, and disease history.

RESULTS

For BMI, the obesity paradox was observed among people with type 2 diabetes (adjusted hazard ratio for obese vs. normal BMI 0.78 [95% CI 0.65, 0.95]) but not among those with CHD (1.00 [0.86, 1.17]). The obesity paradox was pronounced in current smokers, absent in never smokers, and more pronounced in men than in women. For other adiposity measures, there was less evidence for an obesity paradox, yet smoking status consistently modified the adiposity-mortality relationship.

CONCLUSIONS

The obesity paradox was observed in people with type 2 diabetes and is heavily modified by smoking status. The results of subgroup analyses and statistical adjustments are consistent with reverse causality and confounding.

The Evidence for an Obesity Paradox in Type 2 Diabetes Mellitus

Although overweight/obesity is a major risk factor for the development of type 2 diabetes mellitus, there is increasing evidence that overweight or obese patients with type 2 diabetes mellitus experience lower mortality compared with patients of normal weight. This paradoxical finding, known as the "obesity paradox," occurs in other chronic diseases, and in type 2 diabetes mellitus is particularly perplexing given that lifestyle intervention with one goal being weight reduction is an important feature of the management of this condition. We summarize in this review the findings from clinical and epidemiologic studies that have investigated the association between overweight and obesity (usually assessed using body mass index [BMI]) and mortality in type 2 diabetes mellitus and discuss potential causes of the obesity paradox. We conclude that most studies show evidence of an obesity paradox, but important conflicting findings still exist. We also evaluate if potential bias might explain the obesity paradox in diabetes, including, for example, the presence of confounding factors, measurement error due to use of BMI as an index of obesity, and reverse causation.