London School of Hygiene & Tropical Medicine

Teenagers and young adults could reduce the risk of developing nearsightedness by spending more time outdoors, according to a new study published in JAMA Ophthalmology.

Led by the London School of Hygiene & Tropical Medicine and Kings College London, the study found that an increase in UVB exposure was associated with a reduced risk of nearsightedness by just under a third.

Also known as myopia, nearsightedness is a complex condition influenced by environmental and genetic factors. It is becoming more common worldwide, most dramatically in urban Asia, but rises in prevalence have also been identified in the United States and Europe. This has major implications, both visually and financially, for the global burden from this potentially sight-threatening condition.

Previous studies have reported that time outdoors is associated with less myopia but it is uncertain whether this was due to the direct effects of sunlight or to vitamin D. Sunlight exposure, specifically the UVB component, is a main source of vitamin D.

In this study, participants were a random sample of people aged 65 years and older, 371 men and women with myopia and 2,797 without, from six study centres from the European Eye Study. Researchers conducted eye examinations and took blood samples, and estimated exposure to ultraviolet B by interviewing participants on health and behaviour since adolescence.

After adjusting for high levels of education, a well-established risk factor for myopia, they found that participants with the highest UVB exposure, especially in the teenage and young adult years, had about a 30% lower risk for myopia than those with the lowest exposure. The study also found no association with myopia and vitamin D levels or genetic variants in Vitamin D.

Professor Astrid Fletcher, senior author from the London School of Hygiene & Tropical Medicine, said: "We know spending time outdoors can protect against myopia but the reasons why are less clear. Our study showed that exposure to sunlight is likely to be the major factor due to stimulation of physiological factors associated with eye growth, rather than through its action on vitamin D production."

Katie Williams, MRC Clinical Research Fellow and lead author from King's College London, said: "Myopia places an individual at an increased risk of sight threatening conditions, despite correction by glasses or contact lenses, and there is therefore concern this could lead to increasing rates of visual impairment in the future. It appears that sunlight exposure in younger life may be a means to reduce the myopia burden of the future."

The authors acknowledge the study has limitations including measures that were subject to recall and that no data on UVB exposure during childhood was collected.

Publication

• Katie M. Williams, Graham C. G. Bentham, Ian S. Young, Ann McGinty, Gareth J. McKay, Ruth Hogg, Christopher J. Hammond, Usha Chakravarthy, Mati Rahu, Johan Seland, Gisele Soubrane, Laura Tomazzoli, Fotis Topouzis, Astrid E. Fletcher. Association Between Myopia, Ultraviolet B Radiation Exposure, Serum Vitamin D Concentrations, and Genetic Polymorphisms in Vitamin D Metabolic Pathways in a Multicountry European Study. JAMA Ophthalmology. DOI:10.1001/jamaophthalmol.2016.4752

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