Harvard Medical School professor and noted vitamin D expert Dr. Edward Giovannucci is back in the news with an interesting study about the "sunshine vitamin's" effect on the risk of cancer among people with dark skin.

Dr. Giovannucci examined the issue through monitoring the health and mortality rates of some 500 African-Americans patients with more than 43,000 Caucasians over 16 years. The percentages of cancer cases among African-Americans (21 percent) was proportionately larger than Caucasians (16 percent). But that was just the tip of the problem...

The numbers among African-Americans were even worse when it came to overall cancer incidence (30 percent), total cancer mortality (89 percent) and mortality blamed on cancers of the digestive system (124 percent). And, when researchers took vitamin D levels into account, the incidence of cancer hit nearly 60 percent and mortality rates more than doubled to 127 percent.

Although researchers quick not to link low vitamin D levels to cancer, a report I posted a year ago higher amounts of vitamin D reduced the risk of colon, breast and ovarian cancers by up to 50 percent.

That said, be very careful about all forms of oral vitamin D, as it is just too easy to overdose on it. That's why I recommend getting your vitamin D levels checked as soon as you can.