Effects of calcium–vitamin D co-supplementation on glycaemic control, inflammation and oxidative stress in gestational diabetes: a randomised placebo-controlled trial

Randomized, placebo-controlled trial in pregnant women with gestational diabetes mellitus treated at maternity clinics affiliated with Kashan University of Medical Sciences, Kashan, Iran. Participants were adults aged 18–40 years at 24–28 weeks of gestation; the active calcium plus vitamin D arm included 28 randomized women, with 25 completing and 28 analyzed by intention to treat.

Oral calcium carbonate 1,000 mg/day plus vitamin D3 50,000 U twice during the 6-week trial, given at baseline and on day 21. The regimen was compared with placebo capsules/tablets in a randomized placebo-controlled design.

Calcium plus vitamin D co-supplementation improved glycaemic control and several lipid and oxidative stress markers in women with gestational diabetes over 6 weeks. In the active group, 25(OH)D increased by +48.19±46.64 nmol/l (p<0.001), FPG decreased by -0.89±0.69 mmol/l versus +0.26±0.92 in placebo (p<0.001), insulin decreased by -13.55±35.25 pmol/l versus +9.17±38.50 (p=0.02), and HOMA-IR decreased by -0.91±1.18 versus +0.63±2.01 (p=0.001). QUICKI increased by +0.02±0.03 versus -0.002±0.02 (p=0.003), LDL-cholesterol decreased by -0.23±0.79 mmol/l versus +0.26±0.74 (p=0.02), HDL-cholesterol increased by +0.15±0.25 mmol/l versus -0.02±0.24 (p=0.01), GSH increased by +51.14±131.64 μmol/l versus -47.27±203.63 (p=0.03), and MDA increased less than placebo (+0.06±0.66 vs +0.93±2.00 μmol/l, p=0.03). Some inflammatory markers and other oxidative stress measures were not significantly affected.

Small single-center trial with only 28 women in the active arm and a 6-week duration, which limits precision and long-term inference. The population was restricted to pregnant women with gestational diabetes in one Iranian city, so generalizability is limited. Not all inflammatory and oxidative stress outcomes improved, and adverse events were sparse.