For anybody who spends a lot of time in sunlight, vitamin D isn't a problem. In fact, according to WebMD, six days of casual sunlight exposure
without sunscreen will pretty much do it. Even so, huge portions of the country, particularly in the north, are vitamin D deficient. In addition to contributing to seasonal affective disorder, the lack of vitamin D can cause immune problems, skin problems, osteoporosis, and a host of other problems. Luckily, supplements
start at about $2 per bottle.