It is essential to remember, however, that too much sun exposure can burn the skin and potentially lead to skin cancer. Vitamin D helps the body to absorb calcium, which is one of the main building blocks of bone. The body also needs vitamin D to keep the nerves, muscles, and immune system working properly.
Vitamin D deficiencies can cause soft bone conditions such as rickets or osteomalacia, and the porous, fragile bone condition called osteoporosis. However, spending time in the sun without sunscreen can cause sunburn and may contribute to the development of skin cancer. Others may not be able to adequately release vitamin D into their blood circulation from fat cells.
Also, certain individuals may not activate vitamin D to a usable state. These people may find themselves at risk of vitamin D deficiency, including:. In the United States, the recommended daily intake of vitamin D from food or supplements is as follow:.
Some foods are higher in vitamin D than others. Eggs, sardines, and salmon naturally contain vitamin D. Also, manufacturers fortify most milk and some brands of yogurt and breakfast cereals with the vitamin. The University of Florida provides examples of foods that contain vitamin D:.
Vitamin D rich food and supplements are particularly important for people who find it difficult to get the vitamin from exposure to the sun, and those who cannot spend much time outside. Older people, those with darker skin, other groups whose skin is less able to make vitamin D, and individuals at higher risk for vitamin D deficiency may wish to consider taking a supplement. It is worth noting that, while it is rare, vitamin D toxicity can occur and cause nausea, constipation , weakness, and kidney damage.
The latest advice is for adults to get no more than 4, IU of vitamin D a day from food and supplements. Sun exposure typically will not lead to vitamin D toxicity. It is also possible to get vitamin D production from an indoor tanning bed. The Vitamin D Council advise people thinking about this route to:. Sun exposure is the most important natural source of vitamin D.
The body uses the vitamin to absorb the calcium it needs to build and maintain bones. July 18, July 17, Share Tweet Email Print. What's Your Quick Question? Ask us anything:. Have a correction or comment about this article? Please contact us. By: M. Holick, J. MacLaughlin, M. Clark, S. Potts, R. Anderson, I. Blank, J. Parrish and P.
Science, New Series, Vol. Vitamin D was discovered in , culminating the long search for a way to cure rickets, a painful childhood bone disease. Within a decade, the fortification of foods with vitamin D was under way, and rickets became rare in the United States. But solving the problem of rickets was only the beginning of research into vitamin D. Research results suggest that vitamin D may have a role in other aspects of human health.
Vitamin D is one of the 13 vitamins discovered in the early 20th century by doctors studying nutritional deficiency diseases. Ever since, scientists have defined vitamins as organic carbon-containing chemicals that must be obtained from dietary sources because they are not produced by the body's tissues. Vitamins play a crucial role in our body's metabolism, but only tiny amounts are needed to fill that role.
Although vitamin D is firmly enshrined as one of the four fat-soluble vitamins, it is not technically a vitamin. True, it's essential for health, and only minuscule amounts are required. But it breaks the other rules for vitamins because it's produced in the human body, it's absent from all natural foods except fish and egg yolks, and even when it's obtained from foods, it must be transformed by the body before it can do any good. As our habits change, most of us cannot rely on our bodies to produce vitamin D the old-fashioned way.
Instead, we increasingly depend on artificially fortified foods and pills to provide this vital nutrient. Coming full circle in the modern world, this substance may actually come to fit the technical definition of a vitamin. Vitamin D is not one chemical but many. The natural type is produced in the skin from a universally present form of cholesterol, 7-dehydrocholesterol. In contrast, most dietary supplements are manufactured by exposing a plant sterol to ultraviolet energy, thus producing vitamin D 2.
Because their function is almost identical, D 2 and D 3 are lumped together under the name vitamin D — but neither will function until the body works its magic see figure. The sun's energy turns a chemical in your skin into vitamin D 3 , which is carried to your liver and then your kidneys to transform it to active vitamin D. The first stop is in the liver, where vitamin D picks up extra oxygen and hydrogen molecules to become hydroxyvitamin D, or 25 OH D.
This is the chemical that doctors usually measure to diagnose vitamin D deficiencies. But although 25 OH D is used for diagnosis, it can't function until it travels to the kidney. There it acquires a final pair of oxygen and hydrogen molecules to become 1,25 dihydroxy vitamin D; scientists know this active form of the vitamin as 1,25 OH 2 D, or calcitriol, but for ordinary folks the name vitamin D is accurate enough.
Vitamin D's best-known role is to keep bones healthy by increasing the intestinal absorption of calcium. A lack of vitamin D in children causes rickets; in adults, it causes osteomalacia. Both bone diseases are now rare in the United States, but another is on the rise — osteoporosis, the "thin bone" disease that leads to fractures and spinal deformities.
Low levels of vitamin D lead to low bone calcium stores, increasing the risk of fractures. If vitamin D did nothing more than protect bones, it would still be essential.
But researchers have begun to accumulate evidence that it may do much more. In fact, many of the body's tissues contain vitamin D receptors, proteins that bind to vitamin D. In the intestines, the receptors capture vitamin D, enabling efficient calcium absorption. But similar receptors are also present in many other organs, from the prostate to the heart, blood vessels, muscles, and endocrine glands.
And work in progress suggests that good things happen when vitamin D binds to these receptors. The main requirement is to have enough vitamin D, but many Americans don't. Vitamin D deficiencies were rare when most men rolled up their sleeves to work in sunny fields.
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