New research out of Australia has found that sun exposure – independent of vitamin D levels – may have a protective association against the development of allergic disease.
Previous research has shown that low vitamin D levels are associated with atopic disease and allergic sensitization, although the research has sometimes been mixed. Despite extensive study on vitamin D levels, latitude and atopic disease, researchers out of Australia noticed a gap in research documenting sun exposure and atopic disease. As a result, they investigated the link between sun exposure and vitamin D levels and allergic disease.
The researchers looked at participants enrolled in the Tasmanian Infant Health Study. This study was a cohort established in 1988-89 that enrolled babies born during that time. The original cohort began with 1,433 infants. Researchers continued to track this cohort over the years, administering blood tests and questionnaires for different studies. In the final follow-up in 2004-05, only 415 adolescents were actively participating in this study.
In this present analysis, researchers wanted to compare allergic disease (asthma, eczema, and rhinitis) and allergen sensitization to vitamin D levels and reported sun exposure. They wanted to know if vitamin D levels or sun exposure showed a protective association against allergic disease.
Here is what they found:
- There was no significant association between sun exposure in childhood and the occurrence of asthma, eczema, rhinitis or inhalant sensitization.
- However, “higher sun exposure during summer holidays and weekends in adolescence was associated with significantly reduced risk of eczema and rye grass positive rhinitis.”
- Winter sun exposure in adolescence was also protective for eczema.
- These findings were independent of vitamin D levels. This means that vitamin D levels did not correlate with a reduction in these conditions, while sun exposure did.
The greatest strength of this study was the long term follow-up of 16 years. However, its weaknesses include poor data on vitamin D supplementation and dietary intake and lack of data on clothing and sunscreen use.
It has been documented that UV radiation is beneficial for improvement of atopic dermatitis and its ability to down regulate an overactive immune reaction in the skin. This mechanism may explain the observation of a reduction in eczema risk. However, this mechanism does not explain the reduction in risk in allergic rhinitis, which remains unexplained. The researchers state, “This suggests that (the) beneficial effects of UV exposure may be exerted by mechanisms other than reducing allergen sensitization.”
In conclusion, the researchers have opened the possibility that sun exposure may be protective against allergic disease, but they encourage additional research on both ultraviolet light/sun exposure and vitamin D before making sun exposure recommendations.