The study was conducted by a team of researchers led by Cedric F. Garland at the Moores Cancer Center at the University of California, San Diego (UCSD).
As part of the study, researchers combined data from surveys of serum vitamin D levels during winter from 15 countries. The data was then applied to 177 countries to estimate the average serum level of a vitamin D metabolite of people living there.
The study found an inverse association of serum vitamin D with risk of colorectal and breast cancer and estimated that 250,000 colorectal cancer cases and 350,000 cases of breast cancer could be prevented worldwide by increasing intake of vitamin D3, particularly in countries north of the equator.
"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," Garland said.
The researchers suggested that increasing vitamin D levels in populations, particularly those in northern climates, might both prevent and possibly serve as an adjunct to existing treatments for cancer.
"This could be best achieved with a combination of diet, supplements and short intervals - 10 or 15 minutes a day - in the sun. It could be less for very fair-skinned individuals. 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," Garland said.
The findings of the study were published in the August issue of the journal Nutrition Reviews.