Vitamin D appears effective in reducing Colorectal
Cancer incidence
By Valerie DeBenedette, Contributing Writer
Health Behavior News Service
A larger daily dose of vitamin D could reduce the
incidence of colorectal cancer with minimal risk,
according to a new review that pools results from
five studies.
The analysis found that maintaining a
specific target blood level of vitamin D was
associated with a 50 percent lower risk of
colorectal cancer than that seen in people with
consistently lower blood levels.
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. However, a
meta-analysis pools the data from several studies,
thus increasing the strength of the results.
The study is being published in the March issue of
the American Journal of Preventive Medicine.
The five studies 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 milliliter or higher was
associated with a 50 percent lower risk of
colorectal cancer than that seen with blood levels
of 12 nanograms per milliliter 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 IU per day for
vitamin D intake, so this recommendation would be
safe for most people.”
There is no official recommended dietary allowance
for vitamin D, but an adequate dietary intake per
day for most adults is currently considered to be
200 to 400 IU.
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.
“The results are pretty straightforward,” said Karen
Glanz, Ph.D., director of Emory University’s
Prevention Research Center at the Rollins School of
Public Health. However, changing behavior on the
basis of this study may be premature, she said. The
analysis found an association between vitamin D
levels and lowered risk, not a definite link, Glanz
said, but adding vitamin D to the diet or taking a
supplement would probably not do much harm and there
could be a benefit.