Researchers with the Dana-Farber Cancer Institute and the Harvard School of Public Health have found that patients with colon cancer who were among the top 25% in levels of vitamin D before being diagnosed were less likely to die during the study period than those who were among the 25% with the lowest levels of the vitamin.
"Our data suggest that higher prediagnosis ... levels of [vitamin D] after a diagnosis of colorectal cancer may significantly improve overall survival," the researchers write.
Previous research published this year linked higher levels of vitamin D to a reduced risk of colorectal cancer, but the vitamin's effect on cancer survival wasn't known at that time.
For the current study, researchers Kimmie Ng, MD, MPH, and Charles Fuchs, MD, MPH, and colleagues analyzed data from the Nurses' Health Study and the Health Professionals Followup Study and identified 304 patients who had been diagnosed with colorectal cancer between 1991 and 2002. The patients had provided earlier blood samples as part of the previous studies. Their vitamin D levels were checked at least two years before their cancer diagnosis.
The team followed the study participants until 2005 or their death, whichever came first. During that time, 123 patients died; 96 of them from colorectal cancer.
The researchers looked at the previously measured vitamin D levels to see how the levels varied between those who survived and passed away. They discovered that the patients with the highest levels of vitamin D were 48% less likely to die from any cause -- including colon cancer -- than those who had the lowest levels of vitamin D.
The body makes vitamin D after the skin absorbs some of the sun's rays. You can also get vitamin D by eating or drinking fortified foods and beverages, such as milk, cereals, and certain brands of orange juice. However, the typical American diet often does not provide enough vitamin D, since few foods naturally contain the vitamin. The blood test used in this study measured both vitamin D obtained through one's diet and that made by the body.
The study researchers say it's too early to recommend vitamin D supplements to patients with colon cancer, but they encourage future trials to see if such treatment might be beneficial. A study examining vitamin D supplementation in combination with post-surgery chemotherapy is being discussed.
The study appears in the June 20 issue of the Journal of Clinical Oncology.