A large, new study shows that living in a sunny climate appears to reduce women’s risk of developing inflammatory bowel disease (IBD).
An estimated 1.4 million people live with an inflammatory bowel disease, either Crohn’s disease or ulcerative colitis, in the U.S. Both cause persistent diarrhea, fever, abdominal pain & cramping, and sometimes rectal bleeding. Symptoms can become severe & sometimes require surgery. Yet little is known about the causes of these diseases, which are thought to involve a dysfunction of the immune system.
For the study, which was published in the Journal Gut, researchers went through data on more than 238,000 women taking part in the long-running Nurses’ Health Study, which began in 1976. The study collected information on where the women were living at birth, age 15, & age 30.
It also recorded any diagnosis of an inflammatory bowel disease up to 2003. Researchers also followed up with women who reported having inflammatory bowel disease & verified their diagnoses through medical records.
They found that women who got a lot of sunshine & lived in Southern regions had a 52% lower risk of being diagnosed with Crohn’s disease by age 30 and a 38% lower risk of getting ulcerative colitis than those who lived in Northern regions.
That result held up even when researchers tried to rule out other things that might increase a person’s risk for an inflammatory bowel disease, like having a family history. “The differences are pretty drastic. That’s what surprised us the most. Especially when it comes to Crohn’s disease.
We’re seeing a 40% to 50% reduction in risk,” says researcher Hamed Khalili, MD, a gastroenterologist at Massachusetts General Hospital in Boston.
Shedding Light on IBD:
This study confirms previous research from Europe, and it suggests that the amount of UV light exposure from sunlight may play an important role in the development of inflammatory bowel disease, though researchers aren’t sure why.
One theory is that people in sunnier states may have higher exposure to UV light, leading to higher vitamin D levels. Vitamin D is known to help regulate immunity and inflammation. Regional differences in environmental pollution or infections could offer other explanations.
An expert on IBD, Amnon Sonnenberg, MD, MSc, a gastroenterologist at Oregon Health & Science University, Portland, who was not involved in the study comments, “The study was well done, the authors are to be commended. We know quite well that there is a north-south gradient, and this north-south gradient applies to the American continent as well as to Europe."
But he says the reasons behind the regional differences are far from clear cut. For example, he says, studies have shown that miners -- who spend their working hours underground & out of the sunlight -- have less inflammatory bowel disease.
For that reason, he cautions patients against thinking that taking more vitamin D might help their symptoms or lessen their risk if they have a family member who’s affected. People tend to think “vitamin D is going to protect me,” Sonnenberg says, “And there is absolutely no evidence for this.”
WebMD Health News
18 January, 2012