Vitamin D may protect against prostate cancer

With spring on the way, Harvard researchers advise men to get more sun, supplements, and seafood. All are good sources of vitamin D, and a large, lengthy study suggests the vitamin reduces risk of prostate cancer.

About 240,000 men in the United States alone will be told that they have the cancer this year, and around 30,000 of those with the disease will die from it. An 18-year Harvard investigation of 14,916 medical doctors found that 1,066 developed the cancer, and 496 of them suffered a deadly form of it. The researchers say that such tolls can be reduced with the help of vitamin D.

“Our study found that more than two-thirds of the men involved had insufficient vitamin D levels in winter and spring,” says Haojie Li, an instructor at the Harvard Medical School. “Even in the sunnier summer and fall months, more than 10 percent were vitamin D deficient, and more than half had less than optimum amounts of the vitamin in their blood.”

Men (and women) usually can get enough of the vitamin with a balanced diet and modest exposure to summer sunshine. Those who don’t eat fish and dairy foods, spend most of their time indoors, and live in foggy northern climates often fail to get enough D, especially in winter. Over many years, a deficiency may lead to softening of the bones. On the other hand, too much exposure to the sun raises the risk of skin cancer.

Li and her colleagues from Harvard-affiliated Brigham and Women’s Hospital and Harvard School of Public Health measured the amount of two different protein markers in the doctors’ blood. They also investigated different forms of a gene involved with taking D into the body. Men with the lowest levels of the markers and with certain genetic profiles are at greatest risk for prostate cancer, the researchers conclude.

The vitamin D-prostate cancer connection was suspected, and even investigated, before, but other studies, including those at Harvard, did not include a large enough number of men nor were they followed long enough to give a clear picture of the relationship.

Lethal aggression

A major reason scientists think vitamin D might protect against this cancer is that it is more common in sun-starved northern countries, according to Li’s report in the March 19 online edition of PLoS Medicine (PLoS is short for Public Library of Science).

Prostate cancer extracts a greater toll on black men compared with white. This may be related to the fact that people with dark skin make less vitamin D than those with light skin when both are exposed to the same amount of sunlight. Doctors in the Harvard study were predominantly white men of European descent, so more research is needed to determine the role of vitamin D in men of color.

Men with the lowest levels of the two vitamin D markers are at a greater risk for an aggressive, often deadly, form of prostate cancer. This form of the disease involves fast-growing tumor cells likely to spread to the bones and other parts of the body. Moreover, men with insufficient vitamin D who have a particular genetic makeup are especially susceptible to the aggressive cancer. Self-treatment with sunshine, supplements, and foods heavy with D may counteract these risk factors, especially among men aged 65 and older.

Undoubtedly, more studies of sunshine, vitamin D, and prostate cancer will be conducted. In the meantime, results of the Harvard investigation, called the Physicians’ Health Study, clearly show that insufficient vitamin D is a common problem among men of European-descent in the United States. “Improving vitamin D status through moderate sun exposure and vitamin D supplements is essential for optimal health,” the researchers agree. They point out that the vitamin is a requirement for strong bones, so irrespective of its effect on prostate cancer, the supplements can improve overall well-being.