Vitamin D
While the body does need sunshine to collect vitamin D, the amount needed is just 10 minutes a day. The body makes this important vitamin from sunlight on the skin.
Vitamin D is essential in order for the bones and the immune system to stay healthy. It could also help in preventing colon cancer and some other types of cancer. Be sure to put on sunscreen as soon as the 10-minute range has been accomplished if spending time outdoors.
Why People Need Vitamin D
Although the calcium in milk helps to make the bones strong, without vitamin D (calciferol) the calcium won't work. The most important role of vitamin D is to regulate how much calcium is absorbed from the food that is consumed. Most of the calcium goes to building strong teeth and bones. Calcium is also needed to send messages along the nerves and to help the muscles contract (as in when the heart contracts). Vitamin D also plays a role in other bodily functions. This vitamin may also help protect against cancer, particularly colon cancer.
Vitamin D is the only vitamin you do not have to eat. Just step in the sun and let it shine on your skin. The ultraviolet light in the sun's rays makes a type of cholesterol that's found just under the skin into vitamin D3, or cholecalciferol. This gets carried to the liver, where it turns into a more active form. From the liver it goes to the kidneys and becomes even more active. Some stays in the liver and kidneys where it helps the body reabsorb calcium from the blood. Some goes to the bones to help them maintain calcium. The rest of the vitamin D3 goes to the intestines to help absorb calcium from the food ingested.
Vitamin D is found naturally in just a few foods, but is in a different form called vitamin D2 or ergocalciferol. While vitamin D supplements can be found in either cholecalcifereol or ergocalciferol, both work but cholecalciferol is more active.
Vitamin D Requirements
Many researchers complained for years that the RDA for vitamin D was too low for older people. The body makes less vitamin D in the skin as an individual gets older, which is one of the reasons older people have a tendency for fragile bones. In 1997 the RDA was changed to account for age changes. The Institute of Medicine did not set an RDA. Vitamin D amounts are now called Adequate Intakes (AIs) and are based on the amounts needed to sustain a defined nutritional status, or the amount needed to maintain a basic level of good health.
Some nutritionists and physicians believe people need more vitamin D as they get older to keep the bones strong and to avoid osteoporosis (a condition where the bones are thin and brittle and break easily). A study published in The New England Journal of Medicine in 1997 backs this sentiment up. The study showed that women and men over the age of 65 can cut their risk for bone fractures in half by taking 700 IUs of vitamin D and 500 mg of calcium daily.
When the Body is Deficient
A surprisingly large number of people are deficient in vitamin D. A 1998 study showed that nearly half of all people are deficient in vitamin D. Even among young people who are otherwise healthy, the deficiency rate is still around 42 percent. For elderly people who are hospitalized, the vitamin D deficiency rate is about 57 percent. Studies have shown that African American women (ages 15 to 49) who get the RDA every day are still 10 to 30 percent deficient.
It is believed a major reason for people having a vitamin D deficiency is that they are deprived of sunlight. If the high number of deficiencies is correct, not enough people are getting outdoors in the sunlight.
Vitamin D is fat-soluble, so when the body makes a lot - say, by spending a day at the beach - some gets stored in the fatty tissues and liver. When the body has enough to last for a while, it stops producing more. People who are outdoors a lot in nicer weather probably store enough to carry them well into the winter months.
Those people who live in sunny climates probably get enough vitamin D just from their normal activities. However, individuals who live in foggy, rainy or overcast climates (or in areas with high air pollution) may not be getting enough vitamin D. People with darker-colored skin may also not be getting enough vitamin D.
Symptoms of Vitamin D Deficiencies
Children who do not get enough vitamin D develop rickets and their bones do not grow or harden properly. Older adults (especially those who do not get enough sunshine) develop soft, weak and painful bones.
People may be deficient in vitamin D if the following circumstances occur:
- They are older and the skin is not absorbing enough sunlight.
- Housebound people typically do not get enough vitamin D.
- Kidney or liver disease patients cannot convert vitamin D3 into more active forms.
- Drugs such as Questran or Colestid are being taken to lower cholesterol. These drugs block absorption of vitamin D and other fat-soluble vitamins.
- Corticosteroid drugs (such as cortisone, prednisone and dexamethasone) taken for allergies, arthritis, asthma and some other conditions can deplete a person's vitamin D3 level.
- Anticonvulsant drugs such as Dilantin or phenobarbital can interfere with vitamin D.
- Strict vegetarians or vegans get little vitamin D because plant foods do not have a lot of D.
- Alcohol abusers can have vitamin D deficiencies because alcohol blocks the body's ability to absorb and store it.
Foods Containing Vitamin D
Fish oil contains vitamin D, so some of this vitamin can be consumed by eating fish liver, herring, sardines, mackerel, salmon, tuna or other oily fish.
Vitamin D is added to many breakfast cereals. However, most people get vitamin D from fortified milk. This is the reason rickets has almost disappeared.
References
- Alan H. Pressman and Sheila Buff.(2007). The Complete Idiot's guide to vitamins and minerals. New York : Alpha Books
- Brewer, S. (2010). The essential guide to vitamins, minerals and herbal supplements. London : Right Way
- Elson M. Haas, Md & Buck Levin, Phd, Rd.(2006). Staying Healthy with Nutrition: The Complete Guide to diet and nutritional medicine. Berkeley, Calif. : Celestial Art
- Holford, P. (2004). The optimum nutrition bible. London : Piatkus
- Holford, P & Lawson, S.(2008). Optimum Nutrition Made Easy How to achieve optimum health. London : Piatkus
- Lieberman, S. & Bruning, N. (2003). The Real Vitamin & Mineral Book. New York : Avery
- Rodale Health Books.(2009). Healing with vitamins : the best nutrients to slow, stop, and reverse disease. Emmaus, Pa. : Rodale
- Royston, A.(2003). Vitamins and minerals for a healthy body. Oxford : Heinemann Library
- The National Research Council.(1989). Recommended Dietary Allowances, 10th ed, National Academy of Sciences
- Werbach, M. (1993). Nutritional Influences on Illness. 2nd ed. Los Angeles: Third Line Press
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