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Sep 02, 2023

Prostate cancer: Does vitamin D drive cancer rate disparities?

African American men are 1.7 times more likely to develop prostate cancer than

African American men are 1.7 times more likely to develop prostate cancer than other men of color or men of European backgrounds. They are also 2.1 times more likely to die of the disease.

This disparity may be partially explained by a lack of equal access to healthcare many African Americans experience, but not completely.

A new study investigates possible biological causes of this disparity, and finds that it may have to do with skin melanin and the manner in which African American men synthesize vitamin D from the sun.

Researchers at Cedars-Sinai Cancer in Los Angeles, CA, among others, contributed to this study. It appears in Cancer Research Communications.

Vitamin D is a critical micronutrient that promotes good bone health by increasing the absorption of calcium, and it also helps protect against prostate cancer.

The new study found that, by the same token, a lack of vitamin D appears to promote the disease.

The current consensus is that about 40% of Americans are vitamin D deficient. A new study from the Cooper Institute reports that the number may be as high as 76% for African Americans.

The human body produces vitamin D with the help of sunlight. ​Ultraviolet B (UVB) rays striking the skin synthesize a form of cholesterol, 7-dehydrocholesterol, into vitamin D3.

This gets carried in the bloodstream to the liver, where it undergoes a first hydroxylation, and then a second hydroxylation primarily in the kidney to become fully activated vitamin D3.

Certain foods can provide additional vitamin D, and supplements are also available. If you are concerned about being vitamin D deficient, it is a good idea to be tested for deficiency by your physician. A doctor can recommend the appropriate level of supplementation needed based on established guidelines.

It is important to approach vitamin D supplementation carefully, since it is possible to take too much.

Vitamin D plays a significant role in cell maturation. According to urologist Dr. David Shusterman, who was not involved in the study, "vitamin D promotes cellular differentiation, which is the process by which cells mature and become specialized, instead of turning cancerous."

Previous research has supported the role vitamin D deficiency can play in preventing cancer growth, said Dr. Shusterman:

"Some studies have demonstrated that vitamin D possesses several activities that could slow or prevent the development of cancer, including promoting cellular differentiation, decreasing cancer cell growth, stimulating cell death (apoptosis), and reducing tumor blood vessel formation (angiogenesis)."

Lead author of the study, Dr. Moray Campbell, notes that "without sufficient levels of vitamin D to cause them to mature, the cells in a tumor continue to multiply out of control."

Melanin is a complex polymer in our skin, hair, and eyes, and is the main factor in determining their color — the more melanin in the skin, hair, or eyes, the darker their hue.

Melanin also offers protection from the sun's rays, an indispensable attribute for people — such as those of African heritage — from regions characterized by a high number of sunlight hours annually.

​However, according to Dr. Kamlesh Yadav — an instructional associate professor at the School of Engineering Medicine and the Center for Genomic and Precision Medicine at Texas A&M Institute of Biosciences and Technology, not involved in the study — "melanin [also] absorbs and scatters UVB radiation, thereby reducing the amount required for the formation of Vitamin D."

While melanin protects the skin, it also reduces the opportunity for the synthesis of vitamin D.

The researchers found the cells in people of African lineage responded to vitamin D in a unique manner that optimized its use in those climate conditions.

"Their response to vitamin D was very, very different, including which genes the vitamin D receptor was controlling and the magnitude of that control," explains Dr. Campbell.

Living in North America, with fewer hours of sunlight, says Dr. Campbell, "in African American men, this differing response made them more vulnerable to prostate cancer."

Dr. Shusterman characterized the study as "significant because it provides a potential mechanism for the racial disparities observed in prostate cancer incidence and aggressiveness."

Although some previous studies have demonstrated an association between low vitamin D levels and prostate cancer in African American men, said Dr. Yadav, "the exact molecular events that occur upon [vitamin D receptor activation] in the context of prostate cancer [in African American men] was unclear."

This research, he noted, "carried out a comprehensive, multi-omic study to confirm that deficiency in vitamin D results in gene expression changes that are different in [African Americans] when compared to Caucasians."

The study may eventually lead to new nutritional guidelines relating to vitamin D intake, after further research helps revise and refine guidelines regarding optimal levels of vitamin D for various types of people and conditions.

Ahead for the researchers is the exploration of microRNAs involved in gene expression that may one day enable a more robust and complete assessment of prostate health.

The authors of the study are also interested in learning more about how vitamin D deficiency may affect other types of cancers.