Study Provides More Clues into Role of Vitamin D in Cancer Prevention

A new study looking at the relationship between vitamin D serum levels and the risk of colon and breast cancer worldwide has estimated the number of cases of cancer that could be prevented each year if vitamin D3 levels met the objective proposed by researchers.

Cedric F. Garland, Dr.P.H., cancer prevention specialist at the Moores Cancer Center at the University of California, San Diego (UCSD; USA) and colleagues estimate that 250,000 cases of colorectal cancer and 350,000 cases of breast cancer could be prevented worldwide by increasing intake of vitamin D3, particularly in countries north of the equator. Vitamin D3 is available through diet, supplements, and exposure of the skin to sunlight.

"For the first time, we are saying that 600,000 cases of breast and colorectal cancer could be prevented each year worldwide, including nearly 150,000 in the United States alone,” said study co-author Garland. The study, which examines the dose-response relationship between vitamin D and cancer, was published in the August 2007 issue of the journal Nutrition Reviews.

The study combined data from surveys of serum vitamin D levels during winter from 15 countries. It is the first such study to evaluate satellite measurements of sunshine and cloud cover in countries where actual blood serum levels of vitamin D3 had also been determined. The data were then applied to 177 countries to estimate the average serum level of a vitamin D metabolite of people living there.

The study's findings revealed an inverse association of serum vitamin D with risk of colorectal and breast cancer. The protective effect began at levels ranging from 24 to 32 ng per ml of 25-hydroxyvitamin D concentration in the serum. The 25-hydroxyvitamin D level is the primary indicator of vitamin D status. The late winter average 25-hydroxyvitamin D in the United States is approximately 15-18 ng/ml. The researchers maintain that increasing vitamin D levels in populations, especially those in northern climates, has the potential to both prevent and possibly serve as an adjunct to existing treatments for cancer.

The study supports previous studies by Dr. Garland and colleagues (Journal of Steroid Biochemistry and Molecular Biology, February 2007), which found that raising the serum 25(OH)D levels to 55 ng/ml was optimal for cancer prevention. This is the first study, however, to recommend optimal vitamin D serum levels, which, according to Dr. Garland, are high enough to provide the needed benefit but which have been found by other scientists to be low enough to avoid health risks.

"This could be best achieved with a combination of diet, supplements, and short intervals--10 or 15 minutes a day--in the sun,” said Dr. Garland. It could be less for very fair-skinned individuals. He went on to report, "the appropriate dose of vitamin D in order to reach this level, could be very little in a lifeguard in Southern California...or quite a lot for someone in Northern Europe who tends to remain indoors most of the year.”

The serum level recommended by the study would correspond to intake of 2,000 International Units (IU) per day of vitamin D3 for a meaningful reduction in colorectal cancer. The researchers recommend 2000 IU/day, plus, when weather allows, a few minutes in the sun with at least 40% of the skin exposed, for a meaningful decrease in breast cancer incidence, unless the individual has a history of skin cancer or a photosensitivity disease. Dr. Garland also recommends moderate sun exposure and use of clothing and a hat when in the sun longer than 15 minutes.

This study used worldwide data only recently available through a new tool called GLOBOCAN, developed by the World Health Organization's International Agency for Research on Cancer. GLOBOCAN is a database of cancer incidence, mortality, and prevalence for 177 countries. Earlier research from this core group have shown an association between higher levels of vitamin D3 or markers of vitamin D status and lower risk of cancers of the breast, colon, ovary, and kidney.

The researchers emphasized their call for prompt public health action to increase intake of vitamin D3 as an inexpensive tool for prevention of diseases that claim nearly one million lives each year worldwide. "The message is, depending on where you live, you may need to consider taking in considerably higher levels of vitamin D3 than those currently recommended,” said Dr. Garland. "I'd recommend discussing vitamin D needs with a healthcare professional, who may order and interpret a simple blood test for a vitamin D metabolite [25(OH)D], and provide a dosage recommendation that's appropriate for the individual's needs.”


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