A bright light in the cancer fight

Two analyses show vitamin D slashes risk of colorectal and breast malignancies

UNNATI GANDHI

From Wednesday's Globe and Mail

Two meta-analyses at the University of California, San Diego -- the latest in a growing body of evidence touting the benefits of the vitamin -- have found that increasing daily intake of vitamin D could prevent the development of breast cancer by as much as half and that of colorectal cancer by nearly two-thirds.

A meta-analysis is a compilation of published medical literature that, in this case, looked at the association between levels of vitamin D in the blood and the risks of breast and colorectal cancers.

"The evidence is very compelling," said Edward Gorham, a professor of family and preventative medicine at the university's Moores Cancer Center and co-author of both studies. "The association between vitamin D and cancer prevention is very strong and consistent. So from an epidemiological standpoint, it's very convincing."

In the breast cancer study, published online in the Journal of Steroid Biochemistry and Molecular Biology, the researchers divided the records of 1,760 individuals from the compiled studies into five groups, from those with the lowest blood levels of vitamin D to those with the highest. The data also included whether the individuals had developed cancer.

The results showed that those in the group with the lowest vitamin D blood levels had the highest rates of breast cancer, while breast cancer rates dropped by half in those who took 2,000 international units (IU) of the vitamin daily.

In the colorectal cancer study, published online in the American Journal of Preventive Medicine, the researchers divided the records of 1,448 individuals into the same five groups. They found a two-thirds reduction in the incidence of colorectal cancer in those who took 2,000 IU of vitamin D3, the most common form.

Based on the findings, the researchers recommend taking 2,000 IU of the vitamin daily, on top of spending between 10 and 15 minutes in the sun each day, weather permitting

Canada's revised Food Guide, released Monday, only recommends 400 IU daily.

"There's really no downside to taking 2,000 IU of vitamin D, because if we're talking risk versus benefit, it's well known that the adverse effects of doing so are nearly non-existent," Dr. Gorham said.

Vitamin D, produced in the skin as a result of direct exposure to sunlight, is also known to maintain strong bones. It is found in some foods as well, such as salmon and other oily fish, and is routinely added to milk. Dr. Gorham said the average North American gets less than 200 IU of vitamin D a day
.

Supplements are currently the only way to take in the researchers' recommended amount in northern countries such as Canada, where people must cover up during the cold winter months.

Reinhold Veith, director of the Bone and Mineral Laboratory at Mount Sinai Hospital in Toronto, said vitamin D plays a role in normal healthy cell development. It also appears to slow down the reproduction of cancer cells.

Barbara Kaminsky, CEO of the B.C. and Yukon division of the Canadian Cancer Society, said in an interview yesterday that "the power of these meta-analyses reinforce what we've been aware of in the past, but we know that when it comes to cancer, the story is complicated."

In the past, the society has recommended that people reduce exposure to the sun because of the risk of developing skin cancer. But at the same time, the society recognizes that vitamin D may play a role in preventing other types of cancer. As a result, it is recommended that the public take vitamin D supplements.

Ms. Kaminsky said the numbers presented in the study -- a 50-per-cent reduced risk of developing breast cancer and a 67-per-cent reduced risk of developing colorectal cancer -- are significant.

"When you look at the number of women diagnosed with breast cancer in Canada, it's 22,000 a year. If we could cut that down to 11,000, wouldn't that be remarkable?"

But she called for further studies to determine whether there is an advantage to taking more than 2,000 IU of vitamin D a day, and how much time in the sun people with darker skin tones, who produce less vitamin D for every minute of exposure to daylight, would need to achieve the same results