Harvard School of Public Health researcher Kana Wu, MD, PhD, and colleagues looked at data from a large, ongoing study of male health professionals who provided blood samples for analysis. The researchers compared vitamin D levels in the blood of 179 study participants who developed colon or rectal cancer with those of 356 matched participants who did not get cancer.
They found that compared with the men who had the lowest vitamin D levels, those with the highest levels were less likely to get colon or rectal cancer -- particularly colon cancer. The results were even stronger when the researchers combined these data with similar data from a study of female health professionals.
The findings support a number of previous studies that link vitamin D to colon cancer protection, to protection against breast and ovarian cancer, to protection against pancreatic cancer, and to overall reduction of cancer risk.
Interestingly, Wu and colleagues find that the colon cancer-fighting benefit of vitamin D may be limited to people who are not overweight and who exercise regularly. That's because overweight, sedentary individuals tend to suffer insulin resistance, which may increase risk of colon cancer.
"We found that the [colon cancer-protective effect of vitamin D] was much stronger for both lean and physically active men and women but much weaker in overweight and inactive individuals," Wu and colleagues suggest.
The researchers report their findings in the July 18 issue of the Journal of the National Cancer Institute.