Vitamin D deficiencies are increasingly common in the United States. We know this is bad news for our bones, but what about the rest of our bodies? Now, research shows that lacking this important vitamin may increase our risk of developing colon cancer. Colon cancer is the second most common form of cancer in the United States. In 2010, there will be an estimated 143,000 new cases of colorectal cancer.
Exposure to sunlight triggers vitamin D production in our skin. In the 1980s, two doctors (Garland and Garland) noticed that colon cancer was less likely to occur in those living in sunny areas. These doctors hypothesized that there was an association between the two, and this spawned decades of research on vitamin D and colon cancer. The conclusions of many of these studies, however, were inconsistent.
The largest colorectal case-control study known to date was recently published in the American Journal of Epidemiology. The authors pooled and reviewed data from three studies analyzing vitamin D levels and colorectal cancer incidence among more than 600 confirmed cases of colon cancer and almost 800 cancer-free control subjects. They found that people with the highest blood levels of vitamin D had a reduced risk of developing colorectal cancer compared to people with the lowest blood levels of vitamin D. Interestingly, they also noted that among those with adequate levels of vitamin D who also took non-steroidal anti-inflammatory drugs (or “NSAIDS,” such as aspirin or ibproufen), the risk decreased even more.
This study is especially noteworthy because researchers measured actual concentrations of vitamin D circulating in the bloodstream, as opposed to approximating vitamin D status through reported sun exposure or evaluating self-reported dietary or supplement intake. This is an important distinction: conclusions were drawn based on actual measurements of vitamin D status, as opposed to estimated vitamin D status.
Vitamin D has a few responsibilities in the colon. For one, it interacts with cells in the colon, playing a role in controlling their life cycles; cells that, in some cases, can become cancerous. Most importantly, the active form of vitamin D may directly inhibit or combat the development of cancer cells.
So, for your colon’s sake (and your bones, immune system, and mental health): are you getting enough vitamin D? As widespread deficiencies emerge, many doctors are routinely checking vitamin D levels at physicals. If you’re unsure, ask your doctor to check yours. Vitamin D is obtained through sun exposure: fifteen minutes/day a few days per week in the summer is sufficient for most people, though darker skinned people may require more. Good dietary sources include cod liver oil, salmon, mackerel, tuna, and fortified milk. If you have insufficient status (marked by a blood level < 32 ng/mL), you may need to take an additional supplement of 800 to 1000 IU daily, and if your levels are lower than 20 ng/mL, your doctor may put you on a much higher prescription-strength regimen for several weeks to several months to replete you.
Finally, inflammation is a risk factor for colon cancer. In this study we saw that the use of anti-inflammatory drugs was associated with a marked reduction in the risk of colon cancer. It should be noted, though, that evidence is insufficient on the preventative effects of NSAIDS, and there may be health risks associated with taking them regularly, so talk to your doctor about what prevention strategy may be safest for you if colon cancer is a concern.