An article by Dr. Michel Holick in the New England Journal of Medicine claims that current government recommendations for daily intake of vitamin D are far too low. Dr. Holick charges that the RDA of 200 IU per day is inadequate to prevent vitamin D deficiency in many people. He would raise the recommendation to 800-1000 IU per day.
Inadequate vitamin D intake can cause reduced absorption of calcium, which can lead to bone abnormaladies including rickets, osteoporosis, and osteomalacia. It can also cause immune system dysfunction and muscle weakness.
The body manufactures vitamin D when exposed to the sun, with as little as fifteen minutes per day of direct sun exposure being enough for most people. However, due to efforts to reduce skin damage by covering up or using sunscreen, as well as decreased time spent outdoors, a growing number of people are vitamin D deficient. Those living in non-equatorial regions where the sun’s rays are weaker are even more susceptible, especially in winter.
Food sources of vitamin D include oily fish, such as sardines, as well as fortified foods, such as milk. For most people, taking a daily vitamin supplement is an easy way to ensure an adequate intake of vitamin D.