Another good reason to get outside is to increase your vitamin D level. The exhaustive data in this book led me to be taking 2,000 IU of D daily, after a blood test one month ago resulted in my doctor diagnosing me with a deficiency. This topic is big in the medical and health field right now. Holick is the lead proponent of the need for supplementation for those of us living in the northern hemisphere. He also has some very interesting takes on the current “demonization” of exposing one’s skin to sunlight, which he claims is one factor in the rising rates of inadequate or deficient levels of vitamin D. It is also enlightening to see how difficult it really is to raise one’s vitamin D level through diet alone, although it can be done by eating wild ( not farm-raised) salmon, and drinking multiple glasses of fortified mild or eating more than a quart of yogurt a day.I also learned that while it is really bad to get sunburn, it is really useful to be out in the sun enough to develop a tan, although certain skin types have to be careful in how they build up to tanned skin.