A systematic review of 416 medical journal articles affirmed a strong association between higher serum vitamin D levels and a lower risk of bladder, breast, colon, endometrial, esophageal, gallbladder, kidney, ovarian, pancreatic, rectal, stomach, and vulvar cancers, as well as Hodgkin’s and non-Hodgkin’s lymphomas. The review also uncovered lower risks of metastasis and mortality from cancer in patients with higher levels of vitamin D. While vitamin D levels of 20 ng/ml (50 nmol/L) were adequate for bone and muscle health, reduction of cancer risk and mortality required levels greater than 40 ng/ml (100 nmol/L) and fell further with levels above 50 ng/ml (125 nmol/L). The review cautioned that studies showing no benefit for those taking less than 5,000 IU per day might be misleading. [Wimalawansa SJ. Vitamin D’s impact on cancer incidence and mortality: a systematic review. Nutrients. 2025 Jul 16;17(14):2333. Doi: 10.3390/nu17142333.] Is this a fair summary of vitamin D benefits for limiting incidence and severity of cancer?

These data are an accurate reflection of the medical history of those under study and so are a rough guide to a true cause-and-effect relationship between having a demonstrable benefit from vitamin D with respect to cancer incidence and survival. It is only one of many factors that influence a clinical course for such illness, but is enough of an influence to stand out statistically, just looking at blood levels of patients with and without disease.