In a recent prospective cohort study, researchers out of France have found a relationship between resident sun exposure and risk of Crohn’s disease but not ulcerative colitis.
Crohn’s disease and ulcerative colitis are both autoimmune diseases and forms of inflammatory bowel disease. Inflammatory bowel diseases are characterized by a chronic immune response and inflammation in the gastrointestinal tract. In inflammatory bowel diseases, the immune system mistakes food and bacteria as foreign substances and subsequently attacks the cells of the intestines.
Around 1.4 million Americans suffer from inflammatory bowel diseases and it is estimated that the prevalence worldwide peaks at 396 cases per 100,000 persons.
More specifically, Crohn’s disease (CD) is a type of inflammatory bowel disease which can affect any part of the gastrointestinal tract. CD most commonly occurs at the end of the small intestine or beginning of the colon. Additionally, CD can affect the entirety of the bowel wall and can develop patches of diseased intestine with normal areas in between.
Ulcerative colitis (UC), on the other hand, has similar symptoms as CD but only occurs in the large intestine and only affects the lining of the colon. Additionally, those with UC are at a greater risk for colon cancer.
Vitamin D is of interest in inflammatory bowel diseases because of its known role in the immune system and possible role in protecting against some autoimmune diseases. Studies have shown that vitamin D can make immune cells ‘smarter,’ therefore limiting the risk of autoimmune attacks and subsequent disease.
In this present study, researchers collected data from the E3N cohort study which examined hormonal and dietary risk factors for common diseases in women. This large cohort study was conducted from 1990 to 2005 and included 98,995 women aged 40 to 65 who were living in France. These women completed questionnaires every 2 to 3 years on a variety of health and lifestyle matters.
The researchers first identified cases of CD or UC in the self-administered questionnaires. Next, they validated these cases through questionnaires filled out by the women’s physicians. After investigation, 45 women had confirmed CD, 71 had UC, and 7 had indeterminate chronic colitis.
For sun exposure, the women were asked to list their county of residence. Then, the researchers used satellite imagery to determine the average ultraviolet radiation of each county. The researchers wanted to know, does the amount of ultraviolet radiation in each person’s environment affect the risk of inflammatory bowel disease?
The researchers found:
- Median ultraviolet radiation, as measured in units of kJ/m2, was 1.51 per day for CD, 1.60 per day for UC, and 1.59 per day for non-inflammatory bowel disease cases.
- After adjustment, the risk of CD was lower in the group living in counties with highest ultraviolet radiation compared with the lowest (HR=0.49; p = 0.04).
- There was no link found between risk of UC and residential sun exposure.
The researchers concluded,
“This study adds to the available evidence that residential sun exposure is associated with a decreased incidence of CD. Various level of sun exposure may well explain the North-to-South gradient of CD incidence. Vitamin D production through reasonable sunlight exposure may therefore reduce the risk of CD in high-risk populations.”
The researchers pointed out that the low number of inflammatory bowel disease cases and the use of entire county-wide sun exposure for individual level analysis are limitations to their study.
This study shows a relationship between low sun exposure and increased risk of CD. Is vitamin D at the root of this? Further prospective cohort studies and randomized controlled trials should elucidate the relationship here. To read more about vitamin D and Crohn’s disease, click here. For more information on vitamin D and ulcerative colitis, click here.