Vitamin D supplementation reduces insulin resistance in South Asian women living in New Zealand who are insulin resistant and vitamin D deficient – a randomised, placebo-controlled trial

Randomized, placebo-controlled trial in South Asian women living in Auckland, New Zealand. The active vitamin D group included 42 non-diabetic women who were insulin resistant and vitamin D deficient, with mean age 41.8 years and mean BMI 27.5.

Vitamin D3 (cholecalciferol) 100 mg (4000 IU) daily, given as four 25 mg (1000 IU) capsules per day for 6 months. Participants were randomized in a placebo-controlled design; the active regimen was oral supplementation.

Vitamin D supplementation improved insulin sensitivity in these insulin-resistant, vitamin D-deficient women, with benefit emerging once serum 25(OH)D reached about 80 nmol/L. In the vitamin D group, 25(OH)D rose from 21 (11, 40) nmol/L at baseline to 80 (67, 94) nmol/L at 6 months, with 93 (69, 103) nmol/L at 3 months. Insulin resistance improved (P = 0.02), insulin sensitivity improved (P = 0.003), and fasting insulin decreased (P = 0.02), while C-peptide did not change. No adverse effects were seen in serum calcium results at 3 months.

The active intervention arm was small and restricted to South Asian women, limiting generalizability. Follow-up was only 6 months, and the reported outcomes are mainly metabolic surrogate markers rather than clinical endpoints. Cohort ethnicity and some baseline details were reported at the cohort level, and several outcomes were not fully detailed in the extracted text.