Question: why do we need sunlight

Bernard Ennis answered on 16 Nov 2015:

Apart from the fact that the sun is our primary source of energy, we humans also need sunlight to make certain vitamins which our body needs particularly for making us feel good (vitamin D) and for helping our bones to stay strong (vitamin k). This last part has only very recently been discovered and is especially important for people susceptible to osteoporosis (brittle bones) such as the elderly and also post-menopausal women.