11.2019
Author Prof. E. Harms, University Department of Pediatrics Münster

The incidence of chronic inflammatory bowel diseases (IBD) is increasing around the world. The further away from the equator a person lives, the higher their risk of developing IBD is. The Australian working group that wrote about this correlation in 2015 has now presented the results of a case-control study on the possible relationship between sun exposure and the development of chronic IBD [1].
99 patients (0 to 17 years old) and 396 control subjects with a similar age and gender distribution were asked in detail about their sun exposure in defined past periods, particularly investigating the period before the manifestation of the disease (previous summer and winter) in IBD patients. This questionnaire survey has been previously validated against objective measures of sun exposure. Data on the following covariates was collected: ethnicity, sensitivity to sunlight, tanning, sun protection, physical activity, parental smoking habits, family educational level.
Differences in sun exposure between the two groups were most evident at times of leisure such as during holidays and weekends. In both summer and winter, the IBD patients’ exposure to the sun was significantly lower than that of the control subjects. Using a multivariable analysis, the authors found that every additional 10 minutes of sun exposure on weekends and holidays (summer and winter) was associated with the general risk of developing IBD being reduced by 6%.

Comment: Lack of sunlight (UV radiation) may be a factor in the development of chronic IBD. The pathomechanism behind this observation, which is well documented in this article, remains unclear. The obvious assumption is that UV light activates the vitamin D metabolism, thereby influencing the immune system. In animal models, supplementation with vitamin D showed to be effective in improving experimental colitis and, in turn, colitis could be induced through targeted inhibition of the vitamin D metabolism. The role of vitamin D in human IBD is still under debate. In view of the well-documented long-term risks of UV radiation, however, the results of this study by no means advocate excessive sunbathing.

Reference:
[1] Holmes EA, Ponsonby AL, Pezic A et al. (2019) Higher Sun Exposure is Associated With Lower Risk of Pediatric Inflammatory Bowel Disease: A Matched Case-Control Study. J Pediatr Gastroenterol Nutr 69(2):182-188.