We've known about the need for vitamin D for centuries. Rickets caused by vitamin D deficiency started to occur in the 18th and 19th centuries as Europe and the U.S. became industrialized and its prevalence greatly declined in the U.S. after vitamin D milk fortification began in the 1930's. It is only recently that we've learned vitamin D does more than help build strong bones and teeth.

Vitamin D receptors are on almost every cell line in your body and it is easily obtained by going into the sun. Enough full body sun exposure to make your skin slightly red is enough to make 20,000 units of vitamin D. To put that into perspective, a half gallon of milk contains 800 units and the average OTC vitamin D supplement contains 1000 units. With the industrialization of America, the warnings about sun exposure related skin cancer and the usage of sun screens, vitamin D deficiency has become an epidemic. Forty eight percent of adolescent girls in Maine are vitamin D deficient prior to the summer and 20% remain so by its end. Thirty two percent of Boston medical students are deficient and the medical literature has vitamin D deficiency ranging from 30-80% with the highest deficiencies in inner city African American populations in the north east.
Ok, vitamin D deficiency is real. Should you care? Is this just the next vitamin craze or fad?

Vitamin D deficiency as been linked in children to increased incidence of respiratory tract infections and eczema. In Finland in the 1960s a group of newborns were given 2000 units daily for one year and followed for 30 years, they had a huge reduction in Type I diabetes. Maternal deficiency as been associated with increased rates of asthma in their children. In adults it has been linked to increased rates of colon, lung and breast cancer as well as multiple sclerosis. In the elderly it's been associates with osteoporosis and increased rates of falling. The problem with most research is that the studies are based on population studies (epidemiologic and observational studies) and so may be prone to bias. However drug companies are not going to spend millions to research an OTC vitamin supplement and the NIH has yet to do randomized controlled trials on it.

Right now we don't know for sure how much daily vitamin D someone needs. In Canada it's recommended for infants to take 800 units daily. For adults in the U.S. most experts recommend 1000 units daily but some data suggests that may not be enough. The biggest question then is how much is too much. Dr. Sidbury (professor of dermatology at the University of Washington) thinks that less than 10,000 units a day is "probably safe." In the above Finish study the newborns took 1000 units daily for one year and no toxicity was found. What we definitely know is the current U.S. RDA of 400 units a day is woefully inadequate.

A safe recommendation would be for an adult to take 1000-2000 units daily and for a child to take 400-800 units daily.