A long-term U.S. study published online in GUT has shown that living in sunnier climates may lower the chances of developing inflammatory bowel disease, especially in those aged 30 years or over.
The researchers' findings, which support earlier European research, could potentially lead to new therapies and preventive measures.
Crohn's disease and ulcerative colitis are both inflammatory bowel diseases (IBD) that can be extremely painful, need extensive surgery, and often severely affect the individual's quality of life.
Even though recent advances have identified genetic factors that are likely to be involved in the development of IBD, its causes continue to remain largely unknown. The researchers state that given that the overall genetic risk is low to moderate, factors like environment and lifestyle are likely to play a key role.
Their findings are based on data from two studies that tracked the long- term health of nurses. One study called 'Nurses' Health Study I' started in 1976, whilst the second one, 'Nurses' Health Study II' began in 1989.
Both studies recorded information on the area of residence at birth, and at the ages of 15 and 30 years, together with any diagnosis of IBD recorded up to 2003. Every two years all of the 238,000 participants, who were recruited between the ages of 25 and 55 years, received mail to update their health information. None of the participants had any history of IBD at the time of enrollment.
The researchers divided the U.S. states into northern, middle, and southern tiers of latitude for each of the four time zones (eastern, central, mountain, and pacific). In 1992, researchers recorded the residence of just under 176,000 women. By 2003, 257 women were diagnosed with Crohn's disease, and 313 women with ulcerative colitis.
The authors discovered that the diagnosis of IBD was substantially linked with higher latitudes, and by the time a woman was 30 years or older they were more likely to develop IBD.
They also discovered that in comparison to women who lived in northern latitudes, those who resided in southern climates had a 52% reduced chance of developing Crohn's disease by the age of 30 years and were 38% less likely to develop ulcerative colitis. The researchers found that smoking, which is believed to affect the risk of IBD, had no influence on the results.
"A leading explanation for this north-south gradient in the risk of ulcerative colitis and Crohn's disease may be differences in exposure to sunlight or UVB radiation, which is generally greater in southern latitudes. UV radiation is the greatest environmental determinant of plasma vitamin D, and there is substantial experimental data supporting a role for vitamin D in the innate immunity and regulation of inflammatory response."
They continue stating that their results provide assurance for the importance of biological pathways in influencing geographical differences in IBD development and conclude:
"Understanding such pathways could eventually lead to the development of novel lines of therapy as well as interventions that may modulate the risk of incident disease."
Written by Petra Rattue