Observational studies show that a deficiency in vitamin D may be a risk factor for cancer. Researchers wanted to see if vitamin D supplementation reduces the incidence of cancer and precancers in a group with prediabetes and overweight/obesity that is at a greater risk of cancer than the general population. The Vitamin D and type 2 diabetes (D2d) cancer outcomes study (D2dCA) is an adjunct study to the D2d study, which was carried out at 22 academic medical institutions in the United States. Participants had prediabetes, were overweight/obese, and had been cancer-free for the preceding 5 years. Participants were randomly assigned to either 4000 IU of vitamin D3 or a placebo. Cancer and precancer occurrences were discovered using questionnaires during regular study visits. For all reported occurrences, clinical data were gathered and adjudicated. The hazard ratio (HR) of incidence malignancies and precancers was compared across groups using Cox proportional hazard models. There were 89 cancer cases among 2385 individuals over a median follow-up duration of 2.9 years. The risk of incident cancer was 1.07 when vitamin D was compared to placebo. Colorectal adenomatous polyps were found in 239 of the 241 individuals who had incident precancers. For colorectal polyps, the HR for vitamin D versus placebo was 0.83.

Vitamin D supplementation had no effect on the incidence of incident cancer or colorectal polyps in the D2d sample of patients with prediabetes and overweight/obesity who were not chosen for vitamin D deficiency.

Reference: https://academic.oup.com/jcem/article/106/9/2767/6162834