Lenore Greenstein: 'Sunshine vitamin's' bright side: warding off cancer, Type 2 diabetes

Researchers continue to explore the role of vitamins and minerals in disease prevention. The latest evidence for vitamin D is impressive, according to two studies presented recently at a meeting of the American Association for Cancer Research.

The scientists found that women who get lots of vitamin D are less likely to develop breast cancer, adding to the already strong evidence that the "sunshine vitamin" helps prevent many types of cancer.

High levels of vitamin D translated to a 50 percent lower risk of breast cancer, one study found. Even modestly higher levels resulted in risk reduction of 10 percent, which would translate to 20,000 fewer cases a year. A second study, by Canadian researchers, found that women who spent time outdoors or got a lot of vitamin D from their diets or supplements — especially as teens — were 25 percent to 45 percent less likely to develop breast cancer than women with less of the nutrient.

"Exposure to vitamin D at the time breasts are developing, particularly around adolescence, might be important," reported lead researcher Julia Knight of Mount Sinai Hospital in Toronto.

The body makes vitamin D from sunlight, but sun exposure is controversial because of the risk of skin cancer. Many health experts see little harm in 15 minutes several times a week. Vitamin D is found in salmon, tuna and other oily fish, and is routinely added to milk, but diet accounts for very little of the nutrient that makes it into the bloodstream. Many supplements contain the nutrient, but most have an old form, D-2, that is less potent than the harder-to-find D-3. Multivitamins typically contain little D-2 and include vitamin A, which offsets many of D's benefits. So look for D-3 when you are choosing a supplement. Government advisers cannot agree on a recommended daily allowance for vitamin D but say "adequate intake" is 200 international units a day up to age 50, 400 IUs for ages 50-70, and 600 IUs for people over 70. Some scientists have advocated 1,000 IUs a day, but warn people not to overdo it because too much can cause a dangerous buildup of calcium in the body.

Diet is one of the few factors women can modify to affect their risk of developing breast cancer, so the vitamin D evidence is important, said Dr. William Nelson, a cancer specialist at Johns Hopkins School of Public Health.

In addition to preventing breast cancer, vitamin D may also lower the risk of Type 2 diabetes, researchers reported. A team led by Dr. Anastassios Pittas at Tufts-New England Medical Center in Boston saw a 13 percent lower risk of diabetes based on vitamin D intake from supplements. Overall, the lowest risk of diabetes was observed among women with the highest combined intakes of calcium and vitamin D, compared with those with the lowest.

"Based on the latest guidelines set by the Institute of Medicine, only 3 percent of women in our (research) had adequate vitamin D intake, and only 24 percent had adequate calcium intake," Pittas' group reported in the medical journal Diabetes Care.

The researchers say their findings could have "important public health implications" because interventions to raise both vitamin D and calcium intake "can be implemented easily and inexpensively to prevent Type 2 diabetes."

Lenore S. Greenstein is a registered dietitian in private practice in the Naples area.