The study is published online in the current issue of The Journal of Steroid Biochemistry and Molecular Biology. It pooled data from two earlier studies by the Harvard Nurses Health Study and the St. George's Hospital Study that alleged that people with the highest levels of 25-hydroxyvitamin D, 25(OH)D, had the lowest incidences of breast cancer.



The research was based on 1,760 cases of individuals in the two studies and divided them into five equal groups, from the lowest 25(OH)D at less than 13 nanograms per milliliter, to the highest group with 52 nanograms per milliliter.

"The data were very clear, showing that individuals in the group with the lowest blood levels had the highest rates of breast cancer, and the breast cancer rates dropped as the blood levels of 25-hydroxyvitamin D increased," said study co-author Cedric Garland, Dr.P.H. "The serum level associated with a 50 percent reduction in risk could be maintained by taking 2,000 international units of vitamin D3 daily plus, when the weather permits, spending 10 to 15 minutes a day in the sun."

However, women are warned not to run out and start supplementing their diet. There may be other factors that were overlooked in these studies. While the reports are valid, and the research solid, they only represent 1,760 people out of the entire population.

"Meta-analysis is an important tool for revealing trends that may not be apparent in a single study," said co-author Sharif B. Mohr, M.P.H. "Pooling of independent but similar studies increases precision, and therefore the confidence level of the findings."

The authors recommend further research to study individuals for the effect of vitamin D from sunlight, diet and supplements on the risk of cancer.

The dose-response data on 1,448 people in the study were put into order by serum 25(OH)D level and then divided into five equal groups, from the lowest blood levels to the highest.

Co-author Edward D. Gorham, Ph.D said: "We project a two-thirds reduction in incidence with serum levels of 46ng/ml, which corresponds to a daily intake of 2,000 IU of vitamin D3. This would be best achieved with a combination of diet, supplements and 10 to 15 minutes per day in the sun."

Vitamin D3 is available through diet, supplements and exposure to sunlight, or ultraviolet B (UVB) as long as the skin does not tan or burn. In a white woman, it will only take 10 minutes at noontime on a clear day, with 50 per cent skin exposure, to absorb adequate vitamin D. Darker skin will require up to 25 minutes.

It is important to eat a balanced diet. Vitamin D is linked to Calcium absorption, so overdosing on one will throw out the balance and may result in a depletion of one vitamin.

The reports continued and measured Vitamin D's ability to prevent colorectal cancer and found similar results.