New research from New Zealand shows that children who live in South Island of New Zealand have at least three times the risk of bowel disease such as Crohn’s disease (CD) and ulcerative colitis (UC) when compared to those who live on the North Island. According to an article referencing this research, these bowel diseases usually appear in the pre-teen or teenage years and are incurable. The researchers believe that sun exposure and one of its photoproducts, Vitamin D, may play a part, although the low selenium content of the soil may also have an influence on bowel diseases.
In the southern hemisphere, of course, the farther south one travels, the colder and cloudier the weather becomes. Hence, the South Island has far less sun exposure than the North Island.
Although the researchers did not know for sure that the sunlight and vitamin D hypothesis was correct regarding bowel disease, their idea certainly has plenty to back it up. Crohn’s disease is closely correlated to vitamin D deficiency and winter season, indicating an inverse relationship with sun exposure and vitamin D production. A study of female nurses in the US found that “compared with women residing in northern latitudes [in the northern hemisphere] at age 30, the multivariate-adjusted risk for UC for women residing in southern latitudes was less than half.” Also, in a 12-year investigation of hundreds of thousands of bowel disease patients, hospitalizations, and prolonged hospitalizations, for both UC and CD were higher among those who had low sun exposure compared to those with very high sun exposure.
It is important to understand that bowel disease causes malabsorption of nutrients in the gut, leading to diseases of malnutrition. Vitamin D is one of the “nutrients” that may not be absorbed efficiently, and therefore sun exposure, not supplements, may be the only viable source of vitamin D for a person with bowel disease.
So for a healthy gut, sun exposure plays a vital role. Be sure to enjoy safe, non burning sun exposure whenever possible.
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 Limketkai BN, Bayless TM, Brant SR, Hutfless SM. Lower regional and temporal ultraviolet exposure is associated with increased rates and severity of inflammatory bowel disease hospitalization. Aliment Pharmacol Ther. 2014 Sep;40(5):508-17.
 Margulies SL, Kurian D, Elliott MS, Han Z. Vitamin D deficiency in patients with intestinal malabsorption syndromes–think in and outside the gut. J Dig Dis. 2015 Nov;16(11):617-33.