JeremyG,
It's possible. Nutrition certainly has a significant role in other developmental processes. Another explanation is that getting more sunlight means being outside more, which, at least in the case of sports, leads to tracking objects and using your eyes at a sufficient distance to provide the developmental stress for optimal development. I look forward to seeing the science that will come out of this field in the next ten to twenty years and how well it dovetails with our experiences here.