Background: Obesity-associated metabolic syndrome (MetS) is characterized by abdominal adiposity, insulin resistance, and dyslipidemia. Vitamin D deficiency is prevalent in obesity, and supplementation has been hypothesized to modulate body fat distribution and glucolipid metabolism. This meta-analysis compared the metabolic effects of different vitamin D formulations in patients with obesity-associated MetS. Methods: PubMed, EMBASE, Cochrane Library, Web of Science, and CNKI were searched from inception to the search date. Randomized controlled trials enrolling patients with obesity and/or MetS and evaluating vitamin D2, vitamin D3, or active vitamin D versus placebo/no intervention/low-dose vitamin D for ≥8 weeks were included. Primary outcomes were visceral and subcutaneous fat indices; secondary outcomes included fasting glucose, homeostatic model assessment of insulin resistance, and lipid parameters. Effect sizes were pooled as mean difference (MD) or standardized mean difference (SMD) with 95% confidence intervals (CIs); heterogeneity was assessed using I 2 . Results: Fifty randomized controlled trials were included. Vitamin D3 and active vitamin D reduced visceral adiposity (SMD −0.35, 95% CI: −0.50 to −0.20; and −0.40, 95% CI: −0.60 to −0.20; I 2 = 42%), whereas vitamin D2 showed no significant effect (SMD −0.10, 95% CI: −0.25 to 0.05). Vitamin D3 and active vitamin D improved fasting glucose (MD −0.30 and −0.35 mmol/L) and homeostatic model assessment of insulin resistance (SMD −0.40 and −0.45), and lowered LDL (MD −0.30 and −0.25 mmol/L). Benefits were greater with ≥2000 IU/d, intervention duration ≥6 months, and baseline 25(OH)D <20 ng/mL. The Egger test did not indicate significant publication bias ( P = .12). Conclusions: In obesity-associated MetS, vitamin D3 and active vitamin D, particularly at higher doses and longer durations, are associated with reductions in visceral fat and improvements in glycemic control, insulin resistance, and selected lipid indices; vitamin D2 appears less effective.
Huang et al. (Fri,) studied this question.