Vitamin D may turn out to be a ray of hope for men with prostate cancer. Laboratory and population-based research suggest that adequate levels of vitamin D reduce the risk of developing prostate cancer and may help suppress the growth and spread of prostate cancer cells in men who already have it. A significant proportion of older men have suboptimal levels of vitamin D, especially during the winter and spring months. But boosting your vitamin D levels isn't difficult.
Vitamin D has two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D2 is found in fortified milk and dietary supplements. Vitamin D3 is created within the skin after exposure to sunlight. In the body, vitamins D2 and D3 must be converted in the liver and kidneys into 1,25 dihydroxyvitamin D, the biologically active form. 1,25 dihydroxyvitamin D is required for several important body functions, including the absorption of calcium and phosphorus. It also helps promote bone mineralization, the process by which new bone is created as old bone is broken down.
In addition, vitamin D is believed to help maintain a strong immune system and to regulate cell growth, differentiation (the process whereby new cells develop into distinct types of cells), and apoptosis (the programmed cell death that keeps cell proliferation in check). Out-of-control cell proliferation is the hallmark of cancer.
Studies over the years have pointed to an association between geographic location and the risk of dying of certain diseases. For example, people who live in more southerly latitudes (and who receive year-round sunshine) appear to have a lower risk of dying of cardiovascular disease, diabetes, and some cancers, such as colon and breast, than do those who live in northern latitudes. Researchers suspect that the higher sun exposure, which creates more vitamin D in the skin, may be responsible.
Sun exposure also appears to influence a man's risk of developing prostate cancer. Research suggests that men who were born in sun-drenched areas of the United States are about half as likely to develop prostate cancer later in life as men born in an area with low sun exposure. In the study, higher recreational sun exposure in adulthood also cut men's risk of fatal prostate cancer in half.
The sun exposure research is bolstered by studies showing a link between blood levels of vitamin D and prostate cancer. For example, the long-running Physicians' Health Study found that more than two thirds of the nearly 15,000 study participants had inadequate blood levels of vitamin D in the winter and spring. Among men who developed prostate cancer, those with low levels of vitamin D were more likely to have an aggressive form of the disease. This was especially true among men age 65 or older. When the researchers examined a gene involved in converting vitamins D2 and D3 into the active form, they found that a specific variant of the gene increased susceptibility to developing aggressive prostate cancer when blood levels of vitamin D are low.
How Much Vitamin D? The answer is not clear. According to the Institute of Medicine (IOM), an adequate intake of vitamin D is 200 IU per day for people age 50 or younger. Older individuals need more vitamin D because their skin is less efficient in synthesizing the vitamin, and their kidneys are less able to convert it to the active form. Thus, the IOM's recommended daily intake of vitamin D is 400 IU for those age 51 to 70 and 600 IU for people age 71 or older.
According to the National Institutes of Health Office of Dietary Supplements, people at risk are age 50 or over; live in New England or farther north; are homebound; have darker skin; have medical conditions that inhibit fat absorption, such as liver disease or Crohn's disease; or have had part or all of their stomach or intestines removed.
Sources of Vitamin D. It can be difficult to get all of the vitamin D you need through your diet. Vitamin supplements are another option. Over-the-counter multivitamins typically contain 200 to 400 IU of vitamin D, but you can buy supplements that contain higher amounts. When choosing a supplement, look for one that contains vitamin D3, which is more effective than vitamin D2.
The Bottom Line: Even though it's not yet proven that increasing your vitamin D intake will decrease your risk of prostate cancer, there's clearly an association between the two. If you're young, healthy and fair skinned and live in a sunny, more southerly locale, you should be able to satisfy much of your vitamin D requirement with brief sun exposure (10 to 15 minutes without sunscreen on a clear day) two to three times per week.
But if you're age 50 or over or are otherwise at increased risk for vitamin D deficiency, sun exposure probably won't be enough to boost your intake. Also eat more vitamin D-rich foods and take a daily supplement so that your total daily intake is about 1,000 IU. Also, after your 15-minute dose of sunshine, don't forget to apply a sunscreen with an SPF of at least 15 to reduce your risk of developing skin cancer.