Did you know that 40% of the U.S. population is Vitamin D deficient? Make sure during the winter months that you are getting adequate amounts of vitamin D. According to the National Institutes of Health, "Vitamin D is a fat-soluble vitamin that is naturally present in very few foods, added to others, and available as a dietary supplement. Without sufficient vitamin D, bones can become thin, brittle, or misshapen." Vitamin D sufficiency prevents rickets in children. However in adults, vitamin D sufficiency prevents osteomalacia. Calcium and vitamin D also help protect older adults from osteoporosis. In nature, very few foods contain vitamin D. Some of the best sources of vitamin D are the flesh of fatty fish (such as tuna, salmon, and mackerel) and fish liver oils. There are also small amounts of vitamin D found in cheese, beef liver, and egg yolks. The best way to make sure you are getting enough vitamin D is by taking a dietary supplement. There are many dietary supplements containing vitamin D on the store shelves. Most dietary supplements contain only 400IU of vitamin D. The recommended daily allowance (RDA) of how much vitamin D a person should be taking daily varies based upon age.