Crohn’s Disease is a nasty autoimmune bowel disease that causes abdominal pain, inflammation and fibrous tissue buildup. It is increasing in incidence, particularly among people younger than 20, a group that spends less time outdoors each passing year. Unfortunately and unnaturally, young people spend their time in indoor activities, and when venturing outdoors are advised by their parents and medical “experts” to dutifully apply sunscreen, which can reduce the production of vitamin D in the skin by up to 99%.
Crohn’s is closely correlated to vitamin D deficiency, and moderate sunlight exposure coupled with winter supplementation has been recommended in the past to reduce its severity. Fifty percent of Crohn’s patients have levels of vitamin D below 20 ng/ml (very deficient) in winter and 19% in summer.
Suffice it to say (without reviewing the copious research indicating that sunlight and vitamin D correlate to lower risk of many autoimmune diseases), it appears that sunlight exposure may help to reduce the risk of Crohn’s. The latest indication is a study from France, demonstrating that people living in geographic areas of lowest sunlight exposure have a substantially higher risk of Crohn’s disease. This disease is just one of more than 100 that correlate closely to deficiency of sunlight and vitamin D, yet we continue to see warnings by dermatologists to avoid the sun. When will they ever learn?
Non-burning sunlight exposure is a boon to mankind, and it does not cause melanoma. Read my book for more information or see my earlier blogs on the subject of melanoma and sunlight.
 Chouraki V, et al "The changing pattern of Crohn's disease incidence according to age in northern France: a constant increase in the 0-19 years age group (1988-2005)" DDW 2009; Abstract 114.
 Matsuoka, L. et al. sunscreens suppress cutaneous vitamin D3 synthesis. Journal of Clinical Endocrinology & Metabolism 1987; 64:1165-68
 Gilman, J. et al. Determinants of vitamin D status in adult Crohn’s disease patients, with particular emphasis on supplemental vitamin D use. Eur J Clin Nutr. 2006;60(7):889-96
 Nerich, V. et al. Low exposure to sunlight is a risk factor for Crohn's disease. Aliment Pharmacol Ther 2011;33(8):940-945.