In the past several years, on the other hand, researchers have documented widespread deficiencies of vitamin D, the sunshine vitamin, while other studies have indicated that vitamin D deficiency may increase the risk of various cancers and chronic medical conditions such as hypertension, multiple sclerosis, diabetes and heart disease.
One study presented at the annual meeting of the American Association for Cancer Research [April, 2006] concluded that at least half of American adults are deficient in vitamin D (defined as less than 20 nanograms/milliliter) and that these individuals could lower their risk of breast, colon and other cancers by increasing their intake of vitamin D-rich foods or spending more time in the sun.
In a Canadian case-control study involving 972 breast cancer patients and 1,135 healthy controls, women who worked outside or had frequent outdoor activities during their teen years were 40 percent less likely to develop breast cancer later in life. Those who drank 10 or more glasses of milk (fortified with vitamin D) had a 35 percent reduced risk.
Is RDA Too Low?
The recommended daily allowance for vitamin D is 400 IU (600 for persons age 70 and over), and many scientists believe that it should be much higher. Four or five ounces of cooked salmon provide 400 IU of vitamin D. But unless you eat a lot of fatty fish, your best dietary sources are fortified milk (98 IU per cup) and ready-to-eat cereal (40 to 50 IU per cup).
Supplements typically come in 400 IU doses, but doctors believe there is a risk of overdosing at levels greater than 2,000 IU a day. The easiest way to get vitamin D is through exposure to sunlight.
Fifteen minutes in the sun daily with 40 percent of the skin unprotected, will produce 2,000 to 5,000 IU of vitamin D3. On an overcast or cloudy day, more exposure may be needed. Obese and dark-skinned individuals may also need longer exposure.
Vitamin D has long been known to play a major role in maintaining healthy bones. And at least since the 1930s, large observational studies have noted that the incidence of breast, prostate, colon and other cancers is lower in areas close to the equator than in less sunny climates. Data from 47,800 men in the Health Professionals Follow-up Study followed from 1986 to 2000 indicated that men with vitamin D intake of at least 1,500 IU daily had a 17 percent reduced risk of developing cancer and were 29 percent less likely to die of it.
In analyzing 18 studies of colon cancer published between 1966 and 2004, researchers found that 10 of these confirmed a link between inadequate vitamin D and an increased risk of cancer. The authors suggested that an intake of 1,000 IU or more a day could cut a person’s risk of colon cancer by about half.
According to some studies, when vitamin D was present at high levels at the time of diagnosis, the patient responded better to treatment. Several studies have found a higher survival rate for cancers diagnosed and treated during the sunny months (when D levels are most likely to be high).
Vitamin D receptors are located throughout the body, and the vitamin is believed to be a potent inhibitor of cancer cell growth. It also plays a role in regulating the immune system and, as a result, may offer benefits against autoimmune disorders such as multiple sclerosis. Research has also shown that vitamin D can lower blood pressure and reduce inflammation. And a study published in Archives of Internal Medicine found a higher prevalence of hypertension, diabetes, obesity and high triglycerides in vitamin D deficient persons.
When obtained from sunlight (as opposed to diet and supplements), there is no toxic dose of vitamin D. On the other hand, one study found that little or no vitamin D was produced from human skin exposed to sunlight on cloudless days in Boston from November through February.
Persons who spend most of their time indoors get very little sun exposure, regardless of climate. Decreased exposure to sunlight has become more prevalent as Americans have heeded the message to cover up and/or use sunscreen. The American Cancer Society has not made an official recommendation regarding vitamin D supplements or exposure to sunlight.
Much of the evidence comes from observational studies. There are many variables involved, and a person spending considerable time outside may be benefitting from increased physical activity as well as exposure to the sun. More randomized, controlled studies are needed to confirm the cancer-preventive effects of vitamin D.
The skin cancer versus sun exposure controversy is a prickly one. In Australia, where pale-skinned people of Northern European descent are exposed to high levels of ultraviolet radiation, the rate of skin cancer is the highest in the world. The incidence of malignant melanoma, on the rise since the 1930s, has been stabilized in recent years by a “Slip, Slop, Slap” campaign–slip on a shirt, slop on some sunscreen and slap on a wide-brimmed hat.
That is still good advice nearly anywhere...but with recognition of the need for moderation. Spending 10 to 15 minutes in the sun several days a week is not sun worship and will barely give you a tan. It may give you the vitamin D your body needs for good health.
Michelle Herbert Thomas, PharmD, CDE
Clinical Director
Richmond Apothecaries, Inc.
