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Sunlight reduces the risk of inflammatory bowel disease
Last reviewed: 01.07.2025
A long-term US study published in the journal GUT has found that living in sunny countries may reduce the risk of developing inflammatory bowel disease, especially in people aged 30 and over.
Crohn's disease, ulcerative colitis and inflammatory bowel disease often have a significant impact on a person's quality of life.
Although recent research has identified genetic factors that may be involved in the development of inflammatory bowel disease, the causes of its development remain largely unknown. Scientists say that given the overall genetic risk, factors such as environment and lifestyle also play an important role.
Their findings are based on data from two studies that followed nurses' health over time. One study, called Nurses' Health Study I, began in 1976, and the other, called Nurses' Health Study II, began in 1989.
Both studies included information about where participants lived at birth and whether they had inflammatory bowel disease. None of the participants had a history of bowel disease when they enrolled in the studies. Every two years, all 238,000 participants aged 25 to 55 who took part in the studies updated their health information.
The researchers divided the U.S. states into northern, mid-latitude, and southern latitudes for each of four time zones (Eastern, Central, Mountain, and Pacific). In 1992, the scientists registered the residences of just under 176,000 women. By 2003, 257 women had been diagnosed with Crohn's disease and 313 women had ulcerative colitis.
The authors found that bowel disease was significantly associated with more northern latitudes, and that by age 30, women were more likely to develop such diseases.
They also found that compared with women who lived in northern latitudes, those who lived in southern climates were 52% less likely to develop Crohn's disease by age 30 and 38% less likely to develop ulcerative colitis. The researchers found that smoking, which was thought to affect the risk of developing bowel disease, did not affect the results.
The conclusion that the risk gradient for ulcerative colitis and Crohn's disease decreases from north to south is obvious. Scientists attribute this to differences in exposure to sunlight or UV radiation, which is generally higher in southern latitudes. UV radiation is the largest environmental determinant of vitamin D production. And vitamin D plays an important role in innate immunity and regulation of the inflammatory response.
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