Effects of conjugated linoleic acid supplementation on serum C-reactive protein: A systematic review and meta-analysis of randomized controlled trials

The effects of conjugated linoleic acid supplementation on glycemic control, adipokines, cytokines, malondialdehyde and liver function enzymes in patients at risk of cardiovascular disease: a GRADE-assessed systematic review and dose-response meta-analysis

BACKGROUND

The present systematic review and meta-analysis sought to evaluate the effects of conjugated linoleic acid (CLA) supplementation on glycemic control, adipokines, cytokines, malondialdehyde (MDA) and liver function enzymes in patients at risk of cardiovascular disease.

METHODS

Relevant studies were obtained by searching the PubMed, SCOPUS and Web of Science databases (from inception to January 2023). Weighted mean differences (WMD) and 95% confidence intervals (CIs) were pooled using a random-effects model. Heterogeneity, sensitivity analysis, and publication bias were reported using standard methods.

RESULTS

A pooled analysis of 13 randomized controlled trials (RCTs) revealed that CLA supplementation led to a significant increment in fasting blood glucose (FBG) (WMD: 4.49 mg/dL; 95%CI: 2.39 to 6.59; P < 0.001), and aspartate aminotransferase (AST) (WMD: 2.54 IU/L; 95%CI: 0.06 to 5.01; P = 0.044). Moreover, CLA supplementation decreased leptin (WMD: -1.69 ng/ml; 95% CI: -1.80 to -1.58; P < 0.001), and interleukin 6 (IL-6) (WMD: -0.44 pg/ml; 95%CI: -0.86 to -0.02; P = 0.037). However, there was no effect on hemoglobin A1c (HbA1c), homeostatic model assessment for insulin resistance (HOMA-IR), C-reactive protein (CRP), tumor necrosis factor alpha (TNF-α), and alanine aminotransferase (ALT) adiponectin compared to the control group.

CONCLUSION

Our findings showed the overall favorable effect of CLA supplementation on the adipokines and cytokines including serum IL-6, and leptin, while increasing FBG and AST. It should be noted that the mentioned metabolic effects of CLA consumption were small and may not reach clinical importance.

PROSPERO REGISTERATION COD

CRD42023426374.

Conjugated linoleic acid (CLA) as a functional food: Is it beneficial or not?

Conjugated linoleic acid (CLA) has attracted great attention in recent years as a popular class of functional food that is broadly used. It refers to a group of geometric and positional isomers of linoleic acid (LA) with a conjugated double bond. The main natural sources of CLA are dairy products, beef and lamb, whereas only trace amounts occur naturally in plant lipids. CLA has been shown to improve various health issues, having effects on obesity, inflammatory, anti-carcinogenicity, atherogenicity, immunomodulation, and osteosynthesis. Also, compared to studies on humans, many animal researches reveal more positive benefits on health. CLA represents a nutritional avenue to improve lifestyle diseases and metabolic syndrome. Most of these effects are attributed to the two major CLA isomers [conjugated linoleic acid cis-9,trans-11 isomer (c9,t11), and conjugated linoleic acid trans-10,cis-12 isomer (t10,c12)], and their mixture (CLA mix). In contrast, adverse effects of CLA have been also reported, such as glucose homeostasis, insulin resistance, hepatic steatosis and induction of colon carcinogenesis in humans, as well as milk fat inhibition in ruminants, lowering chicken productivity, influencing egg quality and altering growth performance in fish. This review article aims to discuss the health benefits of CLA as a nutraceutical supplement and highlight the possible mechanisms of action that may contribute to its outcome. It also outlines the feasible adverse effects of CLA besides summarizing the recent peer-reviewed publications on CLA to ensure its efficacy and safety for proper application in humans.

The effect of conjugated linoleic acids on inflammation, oxidative stress, body composition and physical performance: a comprehensive review of putative molecular mechanisms

Conjugated linoleic acids (CLAs) are polyunsaturated fatty acids primarily found in dairy products and ruminant animal products such as beef, lamb, and butter. Supplementation of CLAs has recently become popular among athletes due to the variety of health-promoting effects, including improvements in physical performance. Preclinical and some clinical studies have shown that CLAs can reduce inflammation and oxidative stress and favorably modulate body composition and physical performance; however, the results of previously published clinical trials are mixed. Here, we performed a comprehensive review of previously published clinical trials that assessed the role of CLAs in modulating inflammation, oxidative stress, body composition, and select indices of physical performance, emphasizing the molecular mechanisms governing these changes. The findings of our review demonstrate that the effect of supplementation with CLAs on inflammation and oxidative stress is controversial, but this supplement can decrease body fat mass and increase physical performance. Future well-designed randomized clinical trials are warranted to determine the effectiveness of (1) specific doses of CLAs; (2) different dosing durations of CLAs; (3) various CLA isomers, and the exact molecular mechanisms by which CLAs positively influence oxidative stress, inflammation, body composition, and physical performance.

Associations between total dairy, high-fat dairy and low-fat dairy intake, and depressive symptoms: findings from a population-based cross-sectional study

PURPOSE

Evidence on the association between dairy intake and depression is conflicting. Given numerous dietary guidelines recommend the consumption of low-fat dairy products, this study examined associations between total dairy, high-fat dairy, and low-fat dairy intake and the prevalence of elevated depressive symptoms. Associations between dairy products, which differed in both fat content and fermentation status, and depressive symptoms were also explored.

METHODS

This cross-sectional study included 1600 Finnish adults (mean age 63 ± 6 years; 51% female) recruited as part of the Kuopio Ischaemic Heart Disease Risk Factor Study. Dairy intake was assessed using 4-day food records. Elevated depressive symptoms were defined as having a score ≥ 5 on the Diagnostic and Statistical Manual of Mental Disorders-III Depression Scale, and/or regularly using one or more prescription drugs for depressive symptoms.

RESULTS

In total, 166 participants (10.4%) reported having elevated depressive symptoms. Using multivariate logistic regression models, intake in the highest tertile of high-fat dairy products (OR 0.64, 95% CI 0.41-0.998, p trend = 0.04) and high-fat non-fermented dairy products (OR 0.60, 95% CI 0.39-0.92, p trend = 0.02) were associated with reduced odds for having elevated depressive symptoms. Whereas no significant association was observed between intake of total dairy, low-fat dairy, or other dairy products, and depressive symptoms.

CONCLUSION

Higher intake of high-fat dairy and high-fat non-fermented dairy products were associated with reduced odds for having elevated depressive symptoms in middle-aged and older Finnish adults. Given the high global consumption of dairy products, and widespread burden of depression, longitudinal studies that seek to corroborate these findings are required.

The effects of conjugated linoleic acid supplementation on inflammatory cytokines and adipokines in adults: A GRADE-assessed systematic review and dose-response meta-analysis

Background and aims

Many studies have investigated the effect of conjugated linoleic acid (CLA) supplementation on inflammatory cytokines and adipokines. However, the results of these studies are not consistent. Therefore, this systematic review and meta-analysis were designed to comprehensively evaluate the effect of CLA supplementation on inflammatory cytokines and adipokines.

Methods

Randomized controlled trials (RCTs) examining the effects of CLA supplementation on C-reactive protein (CRP), interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-α), adiponectin, and leptin, published up to March 2022, were identified through PubMed, SCOPUS, and ISI Web of Science databases. A random-effects model was used to calculate weighted mean differences (WMDs) with 95% confidence intervals (CI) for 42 studies that included 1,109 participants.

Results

Findings from 42 studies with 58 arms indicated that CLA supplementation significantly decreased IL-6 and TNF-α levels and also slightly increased CRP levels. However, adiponectin and leptin levels did not change after CLA supplementation. A subgroup analysis found that CLA supplementation reduced adiponectin and leptin in women.

Conclusion

Our results demonstrated that CLA supplementation increased CRP levels and decreased TNF-α and IL-6 levels. Therefore, it seems that CLA can have both proinflammatory and anti-inflammatory roles.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier (CRD42022331110).

Molecular mediators of the association between child obesity and mental health

Biological mechanisms underlying the association between obesity and depression remain unclear. We investigated the role of metabolites and DNA methylation as mediators of the relationship between childhood obesity and subsequent poor mental health in the English Avon Longitudinal Study of Parents and Children. Obesity was defined according to United Kingdom Growth charts at age 7 years and mental health through the Short Mood and Feelings Questionnaire (SMFQ) completed at age 11 years. Metabolites and DNA methylation were measured by nuclear magnetic resonance spectroscopy and Illumina array in blood at the age of 7 years. The associations between obesity and SMFQ score, as continuous count data or using cut-offs to define depressive symptoms (SMFQ >7) or depression (SMFQ >11), were tested using adjusted Poisson and logistic regression. Candidate metabolite mediators were identified through metabolome-wide association scans for obesity and SMFQ score, correcting for false-discovery rate. Candidate DNA methylation mediators were identified through testing the association of putative BMI-associated CpG sites with SMFQ scores, correcting for look-up false-discovery rate. Mediation by candidate molecular markers was tested. Two-sample Mendelian randomization (MR) analyses were additionally applied to test causal associations of metabolites with depression in independent adult samples. 4,018 and 768 children were included for metabolomics and epigenetics analyses, respectively. Obesity at 7 years was associated with a 14% increase in SMFQ score (95% CI: 1.04, 1.25) and greater odds of depression (OR: 1.46 (95% CI: 0.78, 2.38) at 11 years. Natural indirect effects (mediating pathways) between obesity and depression for tyrosine, leucine and conjugated linoleic acid were 1.06 (95% CI: 1.00, 1.13, proportion mediated (PM): 15%), 1.04 (95% CI: 0.99, 1.10, PM: 9.6%) and 1.06 (95% CI: 1.00, 1.12, PM: 13.9%) respectively. In MR analysis, one unit increase in tyrosine was associated with 0.13 higher log odds of depression (p = 0.1). Methylation at cg17128312, located in the FBXW9 gene, had a natural indirect effect of 1.05 (95% CI: 1.01,1.13, PM: 27%) as a mediator of obesity and SMFQ score. Potential biologically plausible mechanisms involving these identified molecular features include neurotransmitter regulation, inflammation, and gut microbiome modulation. These results require replication in further observational and mechanistic studies.

Polyunsaturated fatty acids as modulators of fat mass and lean mass in human body composition regulation and cardiometabolic health

It is now recognized that the amount and type of dietary fat consumed play an important role in metabolic health. In humans, high intake of polyunsaturated fatty acids (PUFAs) has been associated with reductions in cardiovascular disease risk, improvements in glucose homeostasis, and changes in body composition that involve reductions in central adiposity and, more recently, increases in lean body mass. There is also emerging evidence, which suggests that high intakes of the plant-based essential fatty acids (ePUFAs)-n-6 linoleic acid (LA) and n-3 α-linolenic acid (ALA)-have a greater impact on body composition (fat mass and lean mass) and on glucose homeostasis than the marine-derived long-chain n-3 PUFA-eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). In addition, high intake of both ePUFAs (LA and ALA) may also have anti-inflammatory effects in humans. The purpose of this review is to highlight the emerging evidence, from both epidemiological prospective studies and clinical intervention trials, of a role for PUFA, in particular ePUFA, in the long-term regulation of body weight and body composition, and their impact on cardiometabolic health. It also discusses current notions about the mechanisms by which PUFAs modulate fat mass and lean mass through altered control of energy intake, thermogenesis, or lean-fat partitioning.

A Greater Flavonoid Intake Is Associated with Lower Total and Cause-Specific Mortality: A Meta-Analysis of Cohort Studies

Introduction: The links between flavonoid intake and mortality were previously evaluated in epidemiological studies. The aim of the present study was to perform a systematic review and meta-analysis of cohort studies evaluating the link of flavonoid consumption with total and cause-specific mortality. Methods: Prospective cohort studies reporting flavonoid intake and mortality data published up to 30th April 2019 (without language restriction) were searched using PubMed, Scopus and EMBASE database. Generic inverse variance methods and random effects models were used to synthesize pooled and quantitative data. Sensitivity analysis was also performed by a leave-one-out method. Results: Overall, 16 articles met the inclusion criteria (nine studies were performed in Europe, five in the USA, one in Asia and one in Oceania); a total of 462,194 participants (all adults aged >19 years) with 23,473 mortality cases were included in the final analysis. The duration of follow-up ranged from 4.8 to 28 years. Most of the studies assessed flavonoid intake using food frequency questionnaires, whereas four studies used interviews and 1 study used 4-day food records. The meta-analysis showed that flavonoid consumption was inversely and significantly associated with total (relative risk (RR): 0.87, 95% confidence interval (CI) = 0.77-0.99) and cardiovascular disease mortality risk (RR: 0.85, 95%CI = 0.75-0.97), but not cancer (0.86, 95%CI = 0.65-1.14) mortality risk. These findings remained robust in sensitivity analyses. Conclusions: The present findings highlight the potential protective role of flavonoids against total and cause-specific mortality. These results support the recommendations for flavonoid-rich foods intake to prevent chronic diseases.

Clinical Advances in Immunonutrition and Atherosclerosis: A Review

Atherosclerosis is a chronic low-grade inflammatory disease that affects large and medium-sized arteries and is considered to be a major underlying cause of cardiovascular disease (CVD). The high risk of mortality by atherosclerosis has led to the development of new strategies for disease prevention and management, including immunonutrition. Plant-based dietary patterns, functional foods, dietary supplements, and bioactive compounds such as the Mediterranean Diet, berries, polyunsaturated fatty acids, ω-3 and ω-6, vitamins E, A, C, and D, coenzyme Q10, as well as phytochemicals including isoflavones, stilbenes, and sterols have been associated with improvement in atheroma plaque at an inflammatory level. However, many of these correlations have been obtained in vitro and in experimental animals' models. On one hand, the present review focuses on the evidence obtained from epidemiological, dietary intervention and supplementation studies in humans supporting the role of immunonutrient supplementation and its effect on anti-inflammatory response in atherosclerotic disease. On the other hand, this review also analyzes the possible molecular mechanisms underlying the protective action of these supplements, which may lead a novel therapeutic approach to prevent or attenuate diet-related disease, such as atherosclerosis.

A higher flavonoid intake is associated with less likelihood of nonalcoholic fatty liver disease: results from a multiethnic study

Limited information exists on the impact of flavonoid intake on nonalcoholic fatty liver disease (NAFLD). We evaluated the link between flavonoid intake, liver tests and risk of NAFLD in a randomly selected sample of US adults (from the National Health and Nutrition Examination Survey, NHANES, 2005-2010). Of the 17,685 participants, 46.9% were men and 45.4% had NAFLD. NAFLD patients had a significantly lower mean flavonoid intake than healthy individuals (111.3±3.6 vs. 201.3±2.3 mg/d, respectively; P<.001). Fatty liver index (FLI) and serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were significantly higher in the first tertile (T1) of flavonoid intake compared with the highest tertile (T3: with the highest flavonoid intake) (FLI: 67.1 vs. 36.2, AST: 31.2 VS 26.8 U/L and, ALT: 34.2 vs. 24.2 U/L, respectively; P<.001 for all comparisons). Adjusted linear regression displayed significant and negative associations between FLI, AST, ALT and flavonoid intake (P<.001 for all comparisons). Multivariable logistic regression showed that the risk for NAFLD significantly decreased as flavonoid intake tertiles increased in a stepwise manner (odds ratio: 0.81, 95% confidence interval: 0.78-0.86). Moderation analysis revealed that C-reactive protein (CRP) strongly modulated the impact of flavonoid intake on FLI; participants with higher CRP levels benefited less from flavonoid intake compared with those with lower CRP concentrations. In conclusions, our results suggest a reverse significant association between flavonoid consumption, liver tests and the risk for NAFLD. Furthermore, CRP was shown to essentially moderate this relationship. These findings support recommendations for consumption of flavonoid-rich foods to prevent cardiometabolic diseases.

The impact of nuts consumption on glucose/insulin homeostasis and inflammation markers mediated by adiposity factors among American adults

BACKGROUND

Inconclusive results have been published regarding the impact of nut consumption on glucose/insulin homeostasis and inflammatory factors. Furthermore, it remains unanswered whether adiposity factors could mediate the association between nut consumption, glucose/insulin homeostasis and inflammatory markers; this is what the current study aims to investigate.

RESULTS

From a total of 16,784 individuals, 48.2% participants were men; overall mean age was 47.2 years. Age-, sex-, energy intake and race-adjusted mean of serum C-reactive protein (CRP)(0.49 to 0.26 mg/dl), apolipoprotein-β (apo- β) (95.6 to 90.8 mg/dl), glucose/insulin homeostasis parameters and triglyceride-glucose index (TyG) index (8.32 to 7.95) significantly decreased as the quartile of nut intake increased (all p < 0.001). We found that all evaluated potential mediators had significant and positive associations with markers of glucose/insulin homeostasis or inflammation (all p < 0.001). With regard to BMI, the mediated effects were significant for the associations between nut consumption and CRP, fasting blood glucose, insulin, hemoglobin A1c (HbA1c), triglyceride to high-density lipoprotein (TG:HDL) ratio and TyG index (all p < 0.001). As for WC, it had mediator impact on CRP, fasting blood glucose, HbA1c, TG:HDL ratio and TyG index (all p < 0.001). apVAT played no mediation role for any association (all p > 0.05).

CONCLUSIONS

This is the first study which quantify the role of nut consumption on inflammatory and glucose/insulin homeostasis markers. Nut intake was inversely associated with inflammatory and glucose/insulin homeostasis markers. Certain adiposity indexes (i.e. BMI and WC) mediated these associations. These findings convey an important message for the crucial role of weight management with dietary recommendations.

METHOD

We extracted data from the National Health and Nutrition Examination Survey (2005-2010) on nut consumption to evaluate the association between nut intake and markers of glucose/insulin homeostasis and inflammation. We assessed whether this link, if any, is mediated or affected by adiposity factors, including body mass index (BMI), waist circumference (WC, marker of central adiposity), anthropometrically predicted visceral adipose tissue (apVAT), visceral adiposity index (VAI, indicator of adipose distribution) and lipid accumulation product (LPA, novel index of central lipid accumulation). Analysis of co-variance and conceptus causal mediation analysis were conducted based on survey design and sample weights.

Effect of magnesium supplements on serum C-reactive protein: a systematic review and meta-analysis

INTRODUCTION

The aim of the study was to undertake a systematic review and meta-analysis of prospective studies to determine the effect of magnesium (Mg) supplementation on C-reactive protein (CRP). Design: Systematic review and meta-analysis of randomised controlled trials (RCTs).

MATERIAL AND METHODS

Data sources: PubMed-Medline, Web of Science, Cochrane Database, and Google Scholar databases were searched (up until December 2016). Eligibility criteria: Randomized controlled trials evaluating the impact of Mg supplementation on CRP. We used random effects models meta-analysis for quantitative data synthesis. For sensitivity analysis was used the leave-one-out method. Heterogeneity was quantitatively assessed using the I² index. Main outcome: Level of CRP after Mg supplementation.

RESULTS

From a total of 96 entries identified via searches, eight studies were included in the final selection. The meta-analysis indicated a significant reduction in serum CRP concentrations following Mg supplementation (weighted mean difference (WMD) -1.33 mg/l; 95% CI: -2.63 to -0.02, heterogeneity p < 0.123; I² = 29.1%). The WMD for interleukin 6 was -0.16 pg/dl (95% CI: -3.52 to 3.26, heterogeneity p = 0.802; I² = 2.3%), and 0.61 mg/dl (95% CI: -2.72 to 1.48, p = 0.182, heterogeneity p = 0.742; I² = 6.1%) for fasting blood glucose. These findings were robust in sensitivity analyses. Random-effects meta-regression revealed that changes in serum CRP levels were independent of the dosage of Mg supplementation (slope: -0.004; 95% CI: -0.03, 0.02; p = 0.720) or duration of follow-up (slope: -0.06; 95% CI: -0.37, 0.24; p = 0.681).

CONCLUSIONS

This meta-analysis suggests that Mg supplementation significantly reduces serum CRP level. RCTs with a larger sample size and a longer follow-up period should be considered for future investigations to give an unequivocal answer.

Impact of vitamin D supplementation on C-reactive protein; a systematic review and meta-analysis of randomized controlled trials

Background

To evaluate the effect of vitamin D supplementation on C-reactive protein (CRP) through a systematic review and meta-analysis of randomized control trials (RCTs).

Methods

PubMed-Medline, SCOPUS, Google Scholar and Web of Science databases were searched (up until April 2016) to identify RCTs evaluating the impact of vitamin D supplementation on CRP. We used random effects models (using DerSimonian-Laird method) as well as the generic inverse variance methods for quantitative data synthesis. For sensitivity analysis, we applied leave-one-out approach. To examine the heterogeneity we used I2 index. Registration code: CRD42016036932.

Results

Among 1274 search items, 24 studies met the inclusion criteria in the final evaluation. Pooling the data together indicated a non-significant decrease in CRP level following administration of vitamin D (weighted mean difference [WMD] -0.26(mg/l), (95% CI -0.75 to 0.22, N = 26 arms, heterogeneity p = 0.042; I² 54.2%). The WMDs for IL6 was 0.67 pg/ml, (95% CI 0.29 to 1.06, N = 16 arms, heterogeneity p = 0.234; I² 19.1%), 0.43 pg/ml, (95% CI 0.08 to 1.05, N = 26 arms, heterogeneity p = 0.120; I² 42.1%), for IL10, and −0.11 pg/ml, (95% CI -0.53 to 0.30, N = 12 arms, heterogeneity p = 0.423; I² 9.2%) for TNF-α, 4.03 pg/ml, (95% CI 3.50 to 4.57, N = 3 arms, heterogeneity p = 0.752; I² 8.1%) for adiponectin. Sensitivity analyses confirmed the robustness of the findings.

Conclusions

This study provided evidence that vitamin D supplementation had no impact on serum CRP, IL10, and TNF-α, while significantly increased serum IL6. We recommend RCTs with longer period of follow-up time (12 months) for future studies to provide explicit results.

Electronic supplementary material

The online version of this article (10.1186/s40795-017-0207-6) contains supplementary material, which is available to authorized users.