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.

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.

Background Previous findings on the association of dietary glycemic index (GI) and glycemic load (GL) with mortality are conflicting. Objectives The aim of this study was to summarize earlier findings on the association between dietary GI and GL and the risk of cardiovascular disease (CVD) and all-cause mortality. Methods A comprehensive literature search was performed of electronic databases, including MEDLINE (PubMed), Scopus, ISI Web of Science, EMBASE, and Google scholar, up to September 2018. Prospective cohort studies that reported GI and GL as the exposure and all-cause or CVD mortality as the outcome were included in the analysis. The random-effects model was used to estimate pooled RR and 95% CIs of all-cause and CVD mortality. Results Eighteen cohort studies with a total of 251,497 participants, reporting 14,774 cases of all-cause mortality and 3658 cases of CVD mortality, were included in the present analysis. No significant association was found between dietary GI and all-cause mortality (RR: 1.07; 95% CI: 0.96, 1.19) and CVD mortality (RR: 1.02; 95% CI: 0.87, 1.20). In addition, dietary GL was not associated with all-cause mortality (RR: 1.08; 95% CI: 0.93, 1.27) or CVD mortality (RR: 1.07; 95% CI: 0.92, 1.25). However, the highest dietary GI, in comparison to the lowest one, significantly increased the risk of all-cause mortality in women (RR: 1.17; 95% CI: 1.02, 1.35). No evidence for a nonlinear association between dietary GI or GL and all-cause and CVD mortality was found (P > 0.05). Conclusions This meta-analysis of prospective cohort studies showed no significant association between either dietary GI or GL and all-cause and CVD mortality in men, but a positive association of GI with all-cause mortality in women.

Objectives:Premenstrual syndrome (PMS) is a common cyclic psychological and somatic disorder which reduces women’s quality of life. Evidence regarding the association between dietary patterns (DPs) and PMS is rare. The study aimed to determine the relationship between dietary patterns and PMS.Design:The case-control study was conducted among women with confirmed PMS and healthy individuals recruited from healthcare centres.Setting:Dietary data were collected using a validated semi-quantitative food frequency questionnaire and DPs were derived using principal component analysis. The association between DPs and likelihood of PMS was determined using logistic regression.Participants:In total, 225 women with PMS and 334 healthy participants aged 20–46 years took part in the study.Results:Three major DPs were identified: (i) ‘western DP’ characterized by high intake of fast foods, soft drink, and processed meats; (ii) ‘traditional DP’ in which eggs, tomato sauce, fruits, and red meat were highly loaded; and (iii) ‘healthy DP’ high in dried fruits, condiments and nuts. After taking all possible confounders into account, individuals in the highest tertile of the western DP were more likely to experience PMS (odds ratio (OR) = 1·49; 95 % CI: 1·01, 3·52), P < 0·001), whilst both healthy and traditional DP was inversely associated with the syndrome (OR = 0·31; 95 % CI: 0·17, 0·72, P = 0·02; OR = 0·33; 95 % CI: 0·14, 0·77, P = 0·01, respectively).Conclusion:The western dietary patterns were positively associated with PMS, whilst the healthy and traditional dietary patterns were inversely associated with it. Further longitudinal studies are required to confirm our findings.

We found that western and plant-based dietary patterns were associated with an increased risk of PCOS. Also, moderate adherence to the mixed dietary pattern was associated with reduced risk of PCOS. To confirm our findings more studies with longitudinal design are required.

Background: Recent studies have suggested that neck circumference (NC) is a supplemental screening measure for diagnosing metabolic complications and might be associated with glycemic parameters. The aim of the present study was to to evaluate the association between NC and glycemic parameters. Methods: We systematically searched the electronic databases (including MEDLINE, Scopus, EMBASE, and Google scholar) up to April 2018. Observational studies that reported correlation coefficient between NC and glycemic parameters were included in the analysis. A random effects model was used to estimate overall Fisher's Z and 95% confidence interval of glycemic parameters including fasting plasma glucose (FBG), serum fasting insulin level, homeostasis model assessment-estimated insulin resistance (HOMA-IR) and glycated hemoglobin (HbA1c). Results: A total of 21 studies (44,031 participants) were eligible for including in the systematic review and metaanalysis. Significant correlations were found between NC and FBG (Fisher's Z = 0.18; 95% CI 0.16, 0.21), serum fasting insulin level (Fisher's Z = 0.34; 95% CI 0.26, 0.41), HOMA-IR (Fisher's Z = 0.36; 95% CI 0.29, 0.43) and HbA1c (Fisher's Z = 0.14; 95% CI 0.09, 0.20). Meta-regression analysis showed that NC were marginally associated with FBG in a linear manner (β = 0.008, P = 0.09); but not related to serum fasting insulin level, HOMA-IR, and HbA1c. Conclusions: This meta-analysis of cross-sectional studies showed that NC was positively correlated with glycemic parameters including FBG, serum fasting insulin level, HOMA-IR, and HbA1c. Further investigations with prospective design are required to confirm these findings.

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Type 2 diabetes mellitus (T2DM) is one of the most important public health issues. Vitamin K supplementation might have favorable effect on risk factors of T2DM. The aim of this study was to perform a systematic review and meta-analysis of interventional studies to examine the effect of vitamin K supplementation on glycemic indices. A systematic search was performed in electronic databases including PubMed, Science Direct, ProQuest, Institute of Scientific Information Web of Science, and Google scholar up to July 2017. We used a random effects model to estimate pooled effect size of fasting blood sugar (FBS), 2-h oral glucose tolerance test (2-h OGTT), fasting insulin (FINS), and homeostasis model assessment-estimated insulin resistance (HOMA-IR). Five clinical trials (533 participants) fulfilled the eligibility criteria of the present meta-analysis. Overall, meta-analysis could not show any beneficial effect of vitamin K supplementation on FBS (-0.91 mg/dl, 95% CI: -2.57, 0.76, p=0.28), FINS (-0.35 μIU/ml, 95% CI: -1.70, 1.00, p=0.61), HOMA-IR (-0.06, 95% CI: -0.32, -0.19, p=0.63), and 2-h OGTT (-4.00 mg/dl, 95% CI: -20.00, 11.99, p=0.62). Sensitivity analysis showed that overall estimates were not affected by elimination of any study. We did not observe any evidence regarding publication bias. In conclusion, vitamin K supplementation had no significant effect on glycemic control in healthy subjects. However, further studies should be performed on diabetic and pre-diabetic patients to determine the effect of vitamin K supplementation on impaired glycemic control.