Effects of different vitamin D supplements on body fat distribution and glucolipid metabolism in patients with obesity-associated metabolic syndrome: A meta-analysis

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 I2. 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; I2 = 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