Although several observational studies have investigated the relationship between vitamin D deficiency and risk of central obesity, the results were inconsistent. We performed a dose-response meta-analysis on epidemiologic studies that evaluated the association of vitamin D status and abdominal obesity in adults. A systematic search was carried out of all published articles, up to May 2020, in five electronic databases, including MEDLINE (Pubmed), EMBASE, Institute for Scientific Information (ISI) (Web of science), Scopus and Google scholar. Forty-one observational studies reported odds ratios (ORs) or relative risks (RRs) with 95% confidence intervals (CIs) for abdominal obesity in relation to serum vitamin D levels in adults were included in the analysis. Using a random effects model, the overall effect size was calculated. Combining 44 effect sizes from 36 cross-sectional studies with 257,699 participants revealed that the highest versus the lowest serum vitamin D level was significantly associated with a 23% decreased odds of abdominal obesity (OR: 0.77; 95% CI [0.71, 0.83]). This inverse association was significant in almost all subgroups based on different covariates. Dose-response analysis showed that each 25 nmol/L increase in serum vitamin D was related to 8% reduced risk of abdominal obesity (OR: 0.92; 95% CI [0.85, 0.99]). When we confined the analysis to 23 effect sizes from 17 studies with representative population (242,135 participants), the same results were obtained (OR: 0.79; 95% CI [0.71, 0.87]). Dose-response analysis indicated that each 25 nmol/L increase in blood vitamin D levels was linked to 10% decreased central adiposity risk in representative populations (OR: 0.90; 95% CI [0.82, 0.99]). This meta-analysis of epidemiologic studies revealed that serum vitamin D level was inversely associated with risk of abdominal obesity in adults, in a dose-response manner. The same findings were obtained in representative populations. Further prospective studies are required to examine the causal association between serum vitamin D levels and abdominal obesity.

Findings from earlier studies on the association between adherence to a Mediterranean diet and risk of overweight/obesity were inconsistent. We summarized cohort studies investigating the association between the Mediterranean diet and risk of overweight and/or obesity and weight change in adults. A systematic search of PubMed, Scopus, ISI Web of Science, and Google Scholar was conducted up to May 2021. Prospective cohorts that examined the Mediterranean diet adherence in adults as the exposure, and overweight and/or obesity or weight change as the outcomes, and reported RRs or β coefficients and 95% CIs as the effect sizes were included. Seven prospective cohort studies were included of which 6 studies (with 244,678 adult participants) reported the risk of overweight and/or obesity, and 4 cohorts (with 436,617 participants) reported the weight change (3 cohorts reported both overweight and/or obesity risk and weight change). Combining 15 effect sizes from 6 cohorts revealed that greater adherence to the Mediterranean diet was significantly associated with a 9% decreased risk of overweight and/or obesity (RR: 0.91; 95% CI: 0.88, 0.94; I2 = 44.7%; PQ-test = 0.031). This association was significant in the case of studies investigating combined overweight and obesity (RR: 0.92; 95% CI: 0.88, 0.96; I2 = 29.4%; PQ-test = 0.166), but not for studies that reported on obesity (RR: 0.68; 95% CI: 0.43, 1.10, I2 = 50.6%, PQ-test = 0.132). Linear dose–response analysis of 6 studies showed a 2% decreased risk of overweight and/or obesity for 1 additional Mediterranean diet score (RR: 0.98; 95% CI: 0.96, 0.99). Each unit increase in the Mediterranean diet score was associated with 0.04 kg less weight gain over 5 y (−0.04 kg; 95% CI: −0.07, −0.02 kg; 13 effect sizes from 4 cohorts). In conclusion, Mediterranean diet adherence is inversely associated with risk of overweight and/or obesity as well as 5-y weight gain and thus has practical importance for public health.

Summary Several epidemiological studies examined the association of serum vitamin D with metabolic syndrome (MetS), but the findings were inconsistent. We conducted a systematic review and dose–response meta‐analysis to quantify the association between blood vitamin D levels and MetS in adults. A systematic search up to December 2020 was conducted in MEDLINE (PubMed), ISI (Web of Science), Scopus, and Google Scholar databases for epidemiological studies that assessed the relation of serum 25‐hydroxyvitamin D (as the exposure) and MetS (as the outcome) in adults. Eligible cross‐sectional studies were restricted to those with representative populations. Finally, 43 studies were included in the analysis (38 cross‐sectional, one nested case–control, and four cohorts studies). Combining 41 effect sizes from 38 cross‐sectional studies included 298,187 general adult population revealed that the highest level of serum vitamin D, compared with the lowest level, was significantly related to a 43% decreased odds of MetS in developed countries (odds ratio [OR]: 0.57; 95% confidence interval [CI]: 0.49–0.65) and 40% in developing countries (OR: 0.60; 95% CI: 0.52–0.70). Linear dose–response analysis (including 222,175 healthy individuals and 39,308 MetS patients) revealed that each 25 nmol/L increase in serum vitamin D level was significantly associated with a 15% decreased odds of MetS (OR: 0.85; 95% CI: 0.80–0.91); however, we found no significant nonlinear association. Meta‐analysis of five prospective studies with 11,019 participants revealed no significant relation (relative risk [RR]: 0.70; 95% CI: 0.37–1.32). This meta‐analysis indicated an inverse association between serum vitamin D concentrations and risk of MetS in general adult populations in cross‐sectional studies in a dose–response manner. However, no significant association was found in a small number of cohorts. More prospective studies are needed to confirm the causality of this relationship.

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Context Findings of previous observational studies that examined the association between circulating vitamin D levels and lipid profiles have been inconsistent. Objective A dose-response meta-analysis of epidemiologic studies was conducted to investigate the relationship between serum 25-hydroxyvitamin D levels and dyslipidemia in adults. Data Sources Electronic databases were searched systematically for articles published up to June 2021. Data Extraction Fifty-seven observational studies and 2 cohort studies that reported odds ratios (ORs) or relative risks (RRs) with 95%CIs for dyslipidemia in relation to serum 25-hydroxyvitamin D levels in adults were included. Data Analysis A high level, vs a low level, of serum 25-hydroxyvitamin D was related to a significant 19% decrease in the odds of hypertriglyceridemia (OR 0.81; 95%CI, 0.74–0.89), an 18% reduction in low high-density lipoprotein cholesterol (HDL-C) (OR 0.82; 95%CI, 0.76–0.89), and an 18% reduction in dyslipidemia (OR 0.82; 95%CI, 0.75–0.91). No significant association was found between a high vs a low level of serum 25-hydroxyvitamin D and risk of high low-density lipoprotein cholesterol (LDL-C) levels (OR 0.86; 95%CI, 0.62–1.19) or hypercholesterolemia (OR 1.03; 95%CI, 0.93–1.15). Dose-response analyses demonstrated that each 10 ng/mL increase in the serum 25-hydroxyvitamin D level was linked, respectively, to a 7% (OR 0.93;95%CI, 0.85–1.02), a 3% (OR 0.97; 95%CI, 0.90–1.05), and a 4% (OR 0.96; 95%CI, 0.92–1.00) marginally significant decrease in the odds of hypertriglyceridemia, low HDL-C, and dyslipidemia. Conclusion Higher serum 25-hydroxyvitamin D levels are associated with significant reductions in the odds of hypertriglyceridemia, low HDL-C, and dyslipidemia in a dose-response trend. Systematic Review Registration PROSPERO registration no. CRD42021219484.