Vitamin D is important for cancer control. Recent research: Women with breast cancer who had the highest levels of vitamin D were 44% more likely to survive the disease. When researchers at University of California, San Diego, looked at patients with ­colon cancer, those with the highest levels were 37% more likely to survive than those with the lowest.

Other recent cancer studies show that people with high levels of vitamin D have a 25% reduced risk for bladder cancer…54% reduced risk for melanoma…and 52% greater chance of surviving lymphoma.

The only way to accurately determine if you have a low level of vitamin D is to test your blood for 25-hydroxyvitamin D, a metabolite of vitamin D-3. I recommend a test three times a year, in September, January and May. 

What to do: Ask your doctor for a test…or order a test yourself from ­…or order a home test from the Vitamin D Council.

I recommend aiming for a blood level between 50 ng/mL and 90 ng/mL. It is impossible to achieve the recommended level from foods alone—even a D-rich diet provides a maximum of 350 IU daily. Better: Take a vitamin D supplement, 1,000 IU to 5,000 IU daily.