Sunlight and vitamin D linked with protection from inflammatory bowel disease

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Crohn’s disease is one of the two main ‘inflammatory bowel diseases’ (the other being ‘ulcerative colitis’). The condition is generally believed to be ‘auto-immune’ in nature – which means the body’s immune system is reacting against its own tissues (in this case, the bowel wall). Crohn’s disease can affect any part of the gut, and can give rise to symptoms such as bloating, discomfort and bloody diarrhoea. It is usually treated medically with steroids and immunosuppressant agents. Occasionally, surgical removal of diseased bowel is deemed necessary.

In recent years, there has been some growing interest in the role of vitamin D in autoimmunity, with lower levels of vitamin D being linked with enhanced risk of autoimmune conditions. I was interested to read a recent study [1] that found that low sunlight exposure is associated with an increased risk of Crohn’s disease. ‘Epidemiological’ studies of this nature do not prove that sunlight can prevent Crohn’s disease. However, the fact that sunlight stimulates vitamin D production and that this substance also seems to help quell autoimmunity does suggest a ‘causal’ relationship between sunlight and Crohn’s disease.

This is not the only evidence which suggests that sunlight and vitamin D have some relationship with Crohn’s disease. In a study published in 2009, vitamin D levels were found to be lower in Crohn’s disease sufferers than with individuals without this condition [2]. Plus, in those with severe disease, sun exposure and vitamin D levels tended to be especially low.

What is more, there is evidence that limiting vitamin D availability in animals can induce inflammatory bowel disease. Giving them vitamin D can help control auto-immune related disease too [3].

There is also a human study in which individuals with Crohn’s disease were treated with vitamin D3 (1200 IU per day) or placebo (inactive medication) for 12 months [4]. The relapse rate in the placebo group was 29 per cent, compared to just 13 per cent in the group treated with vitamin D (although this result was not statistically significant).

As a whole, the evidence suggests that optimising sun exposure and vitamin D levels is a prudent measure for sufferers of Crohn’s disease, and sufferers of other autoimmune conditions too.


1. Nerich V, et al. Low exposure to sunlight is a risk factor for Crohn’s disease. Aliment Pharmacol Ther. 2011;33(8):940-5

2. Joseph AJ, et al. 25 (OH) vitamin D level in Crohn’s disease: association with sun exposure & disease activity. Indian J Med Res. 2009;130(2):133-7

3. Ardizzone S, et al. Vitamin D and inflammatory bowel disease. Vitam Horm. 2011;86:367-77.

4. Jørgensen SP, et al. Clinical trial: vitamin D3 treatment in Crohn’s disease – a randomized double-blind placebo-controlled study. Aliment Pharmacol Ther. 2010;32(3):377-83

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