Previous studies had shown that lower blood levels of vitamin D did not protect against colorectal cancer, according to lead author Edward Gorham, Ph.D., a research epidemiologist with the Naval Health Research Center in San Diego. The review pooled results from five studies. Those looked at serum collected from healthy volunteers who were then followed for periods ranging from two years to 25 years. There were 535 cases in the pooled analysis and 913 controls, or 1,448 total participants.
The researchers found that a blood serum vitamin D level of 33 nanograms per millilitre or higher was associated with a 50 percent lower risk of colorectal cancer than that seen with blood levels of 12 nanograms per millilitre or lower.
Vitamin D levels in the body are a factor of both diet and sun exposure. Exposing the skin to the sun lets the body synthesize vitamin D, which is why mortality due to colorectal cancer may be higher in geographic areas that get less sunshine.
The amount of dietary vitamin D needed to reach the serum levels that appear to be protective against colorectal cancer — 1,000 to 2,000 international units a day — would not pose any risk, according to Gorham: “The Institute of Medicine has set a ‘No Adverse Effect Level’ of 2,000 international units (IU) per day for vitamin D intake, so this recommendation would be safe for most people.”
Small amounts of sun exposure would also help people boost their vitamin D levels. Fifteen to 20 minutes per day without sunscreen is enough for the body to synthesize 10,000 IU of vitamin D with minimal risk of sunburn or skin cancer, Gorham said.
MEDICA.de; Source: Health Behavior News Service