Vitamin D is required by the body for the regulation of the minerals calcium and phosphorus and also plays an important role in maintaining bone integrity. Vitamin D is found in relatively few foods, many of which are not eaten commonly, such as herring, sardines, and tuna. Beef liver, cheese, egg yolks, and mushrooms provide smaller amounts. More commonly, people get vitamin D from foods that are "fortified". This includes dairy products, juices, and cereals.Vitamin D is known as the "sunshine vitamin" because the main way that people receive vitamin D is through sun exposure. Ten to 15 minutes of exposure of sunshine to the hands, face, arms, and legs, 3 times weekly is sufficient to produce the body's requirement of vitamin D. During the winter months in the northern half of the United States, however, the sun is not strong enough for the skin to make vitamin D. In fact, if you live north of the 42-degrees latitude (a line drawn on a map from the northern border of California to Boston, Massachusetts), you will have a difficult time getting enough vitamin D from the sun from November through February. Increasing vitamin D intake, either through dietary sources or vitamin supplementation, is recommended during this period of time.
Certain groups of people may be particularly affected by this seasonal inability to generate vitamin D from the sun. Older individuals are at risk for developing vitamin D deficiency because their skin doesn't make vitamin D as efficiently as when they were young. Likewise, people with dark skin have less ability to produce vitamin D from the sun.
The FDA has developed the following guidelines for the amount of vitamin D (in International Units) that is recommended on a daily basis:
- Birth to 12 months---400 IU
- Children 1-13 year---600 IU
- Teens 14-18 years---600IU
- Adults 19-70 years---600 IU
- Adults 71 years and older---800 IU
- Pregnant and breastfeeding teens and women---600 IU
These amounts, however, are conservative compared to the recommendations of some authorities, who suggest considerably higher daily doses. For example, The National Osteoporosis Foundation recommends vitamin D 400 IU to 800 IU daily for adults under age 50, and 800 IU to 1000 IU daily for older adults.
Based to a large degree on its geographic location and reduced sun exposure, Osteoporosis Canada now recommends 400-1000 IU daily for adults under the age of 50 years and 800-2000 IU daily for adults over the age of 50 years. Furthermore, the Canadian Cancer Society recommends 1000 IU/day during the fall and winter for adults in Canada.
Despite the importance of vitamin D synthesis to the maintenance of health, it must be remembered that exposure to sunlight is a well-known risk for the development of skin cancer. When sun exposure exceeds more than a few minutes, it is important to wear protective clothing and a sunscreen with a SPF of 8 or higher. Although tanning beds will allow the skin to produce vitamin D, they may be associated with an even higher risk for the development of skin cancer than sun exposure.
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