Calcium-vitamin D cosupplementation influences circulating inflammatory biomarkers and adipocytokines in vitamin D-insufficient diabetics: a randomized controlled clinical trial.

Randomized controlled clinical trial with stratified block randomization in adults with type 2 diabetes and vitamin D insufficiency in Isfahan, Iran. Active intervention arms included calcium (n=29), vitamin D (n=29), and calcium plus vitamin D (n=30), with 118 total completers across four arms.

Three oral active regimens were tested for 8 weeks: calcium carbonate 1000 mg/day, vitamin D3 50,000 IU/week, or the combination of calcium carbonate 1000 mg/day plus vitamin D3 50,000 IU/week. Placebo was used as the comparator.

Overall, calcium and/or vitamin D supplementation improved inflammatory biomarkers, with the combined calcium-plus-vitamin D regimen showing the clearest benefit. IL-6 decreased in all active arms versus an increase in placebo (Calcium −2 Ϯ 1, Vitamin D −4 Ϯ 1, Ca+D −4 Ϯ 1, Placebo 3 Ϯ 1; P < .001), and TNF-α also fell significantly in adjusted models (Model 1 P = .04), although the effect was not significant after further adjustment (Model 2 P = .23). Leptin declined more in the active arms than placebo, while adiponectin changes were not significantly different after adjustment; hs-CRP did not show a significant between-group difference. The main takeaway is that joint calcium–vitamin D supplementation may help reduce systemic inflammation in vitamin D-insufficient adults with type 2 diabetes.

Short 8-week duration and modest arm sizes limit certainty about durability and clinical relevance. Several outcomes were inconsistent across adjustment models, and some endpoints such as adiponectin and hs-CRP were not significant. Usual diet and physical activity were self-reported, and generalizability is limited to vitamin D-insufficient Iranian adults with type 2 diabetes.