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The researcher explained that the results are of particular importance to Black men. This is for a number of reasons. Compared with white men, Blacks have a higher incidence of prostate cancer. Comparatively, their disease is more aggressive, which leads to higher mortality rates. Hollis noted that Black men also exhibit a high prevalence for vitamin D deficiency.

“My colleagues and I think a lack of vitamin D is one of the reasons for health disparities among Black populations. This population has chronically low levels of vitamin D, and they suffer inappropriately from many diseases because of it,” explained Hollis. “It’s a hard thing to prove, but if you look at the Physicians’ Health Study and you look at the Black physicians in there, it appears as though just being Black is a risk to your health. This community is more susceptible to cancers in general, to more aggressive cancers in particular, to more overall diseases—and no one knows why. It’s not because of a lack of medical treatment, because compared to others in the Physicians Health Study the Black physicians get at least the same or better medical care.”

Vitamin D enhances immune function, Hollis explains. Vitamin D has been studied in the treatment of breast cancer and colon cancer in addition to prostate cancer. He explained that one of the ways it probably acts is by reducing inflammation, since it is known to be an anti-inflammatory agent. For example, it lowers C-reactive protein (CRP). Breast cancer, colon cancer, and especially prostate cancer are linked to inflammatory processes. Vitamin D also causes cancer cells to enter into an apoptotic cascade.


Although the federal government recommends a daily amount of 400 IU of vitamin D, Hollis says, “That’s barely enough for an infant, let alone a full-grown person. Vitamin D is not really a vitamin. It’s a prehormone that’s made in your body. You just need sun exposure to start the cycle. It’s a steroid hormone, like estrogen or testosterone. You can make 10,000 to 20,000 IU of vitamin D in 1 day of total body sun exposure. People in sun-enriched environments make a lot of vitamin D, and its level in their blood is quite high.2

“Different systems in the body require different amounts of vitamin D to reach a threshold. If you’re talking about bone disease, then you need very little vitamin D to make it right. And that’s where the problem lies, because everything is based on the small amount it takes for bone health and not the amount it takes for all these other systems. All the randomized studies have been based on skeletal trials; they have not been trials to prevent or treat cancer, autoimmune diseases, or inflammatory processes. What we get in our diets is usually enough to keep us from getting bone disease, but it’s not enough to keep us from getting these other diseases.”

A healthy blood level of vitamin D should be 50 to 70 ng/mL. Hollis concludes that to maintain this level, the general population should get at least 4,000 IU of vitamin D daily.

Bette Weinstein Kaplan is a medical writer based in Tenafly, New Jersey.  


1. Marshall DT, Savage SJ, Garrett-Mayer E, et al. Vitamin D3 supplementation at 4000 international units per day for one year results in a decrease of positive cores at repeat biopsy in subjects with low-risk prostate cancer under active surveillance. J Clin Endocrinol Metab. 2012;97(7):2315-2324

2. Hollis BW. Vitamin D in the prevention and treatment of cancer. Talk presented at: American Chemical Society 249th National Meeting & Exposition; March 22-26, 2015; Denver, CO.