Vitamin D has been shown to slow the rate of tumor growth, as well as trigger the self-destruction of cells developing improperly. Researchers say that cancer patients diagnosed in high-sunlight seasons have higher concentrations of vitamin D in their blood, which "is associated with improved survival, especially in lung and breast cancer patients," according to the study that appeared in the International Journal of Cancer.
The study, led by Dr. Henrik Moller of the Thames Cancer Registry at King's College London, included nearly 1.5 million men and women diagnosed with cancer between 1971 and 2002. It found that those diagnosed in the summer and fall experienced a 6 percent overall reduction in death rate. Women with breast cancer experienced a 14 percent lower death risk when diagnosed in a sunny season -- defined by the study as June 1 through November 30.
"We found sunlight exposure to be a predictor of cancer survival," researchers wrote. "Our results add to a growing body of evidence that vitamin D may play an important role in cancer survival."
The study did not take into account the intensity of sunlight, which is much stronger in summer and would have a larger impact on vitamin D levels.