Guggenheim, J.Williams, C.Northstone, K.Howe, L.Tilling, K.St Pourcain, B.McMahon, G.Lawlor, D.2016-09-052016-09-052014Investigative Ophthalmology and Visual Science, 2014; 55(12):8550-85580146-04041552-5783http://hdl.handle.net/2440/100932Purpose: More time outdoors is associated with a lesser risk of myopia, but the underlying mechanism is unclear. We tested the hypothesis that 25-hydroxyvitamin D (vitamin D) mediates the protective effects of time outdoors against myopia. Methods: We analyzed data for children participating in the Avon Longitudinal Study of Parents and Children (ALSPAC) population-based birth cohort: noncycloplegic autorefraction at age 7 to 15 years; maternal report of time outdoors at age 8 years and serum vitamin D2 and D3 at age 10 years. A survival analysis hazard ratio (HR) for incident myopia was calculated for children spending a high- versus low-time outdoors, before and after controlling for vitamin D level (N = 3677). Results: Total vitamin D and D3, but not D2, levels were higher in children who spent more time outdoors (mean [95% confidence interval (CI)] vitamin D in nmol/L: Total, 60.0 [59.4-60.6] vs. 56.9 [55.0-58.8], P = 0.001; D3, 55.4 [54.9-56.0] vs. 53.0 [51.3-54.9], P = 0.014; D2, 5.7 [5.5-5.8] vs. 5.4 [5.1-5.8], P = 0.23). In models including both time outdoors and sunlight-exposure-related vitamin D, there was no independent association between vitamin D and incident myopia (Total, HR = 0.83 [0.66-1.04], P = 0.11; D3, HR = 0.89 [0.72-1.10], P = 0.30), while time outdoors retained the same strong negative association with incident myopia as in unadjusted models (HR = 0.69 [0.55-0.86], P = 0.001). Conclusions:Total vitamin D and D3 were biomarkers for time spent outdoors, however there was no evidence they were independently associated with future myopia.en© 2014 The Association for Research in Vision and Ophthalmology, Inc.Myopia; Refractive error; Epidemiology; Vitamin D; Light levelsJournal article003004270210.1167/iovs.14-158390003472223001032-s2.0-84920065265232724Lawlor, D. [0000-0002-6793-2262]