Time Spent Outdoors Partly Accounts for the Effect of Education on Myopia

UK Biobank plus ALSPAC and Generation R child cohorts (two-sample multivariable MR; participant counts not stated in abstract)

Adults (UK Biobank) with childhood cohorts used to validate the time-outdoors polygenic score

Two-sample multivariable Mendelian randomisation using genetic instruments for years of education and for time spent outdoors, decomposing the education-myopia causal effect into a portion mediated by being indoors and a portion attributable to other mechanisms such as near viewing. Outcomes were adult spherical equivalent and early age of onset of spectacle wear (age 15 or below).

Time spent outdoors has a small but real genetic component (heritability 9.8%) that tracks from childhood into adulthood. A polygenic score for years of education was INVERSELY associated with children's time outdoors - genetically more education-prone children spend less time outside. Accounting for time outdoors in multivariable MR shrank the causal effect of education on myopia from -0.27 D/year (95% CI -0.41 to -0.13) to -0.17 D/year (95% CI -0.32 to -0.01), a 40% reduction. Comparable results for early age of onset of spectacle wear. The authors conclude about half the education-myopia relationship may be mediated by children not being outdoors during schooling.

Genetics is the instrument, not the confound. The finding is the mechanistic bridge in this topic: it ties the randomized outdoor-time trials (which show outdoor time prevents myopia incidence) to the MR education-causes-myopia result, and identifies the school schedule itself - hours indoors - as roughly half of why schooling damages eyesight.