Vitamin Supplements

Vitamin D is not like other vitamins. Because the body can manufacture this nutrient, in fact, vitamin D fails to meet the classic definition of a vitamin. Vitamin D is manufactured in the skin, with ultraviolet light driving the process. With regular exposure to sunlight, most people can manufacture enough of this vitamin to meet all of their needs. People who do not get enough year-round exposure, however, may require dietary D as well. Certain groups, including older people, have difficulty producing vitamin D themselves and may also require dietary D.

While rickets, a disease caused by a vitamin D deficiency, has been around for thousands of years, our knowledge of the vitamin itself has a relatively short history. It was first isolated and synthesized.

Forms of Vitamin D

The umbrella term vitamin D actually refers to a family of fat-soluble compounds. D vitamins, also called calciferols, come in many forms. Only two are important to the human body, however. These two—D₃ (a natural form) and D2 (a synthetic form)—are equally useful to humans.

•  Vitamin D3, also called cholecalciferol, is formed when sunlight strikes the skin. This is the type of vitamin D contained in foods of animal origin.
• Vitamin D2, or ergocalciferol, is produced through irradiation of a substance in plants called ergosterol. Vitamin D₂ is common in vitamin supplements and in fortified foods such as milk.

Vitamin D and body Functions

• Vitamin D ensures that the body has enough calcium and phosphorous by increasing absorption of these minerals, both necessary for proper formation of bones and teeth; vitamin D also regulates the amounts of calcium and phosphorous in the blood.
• Vitamin D stimulates the production of insulin in the pancreas. People who have vitamin D deficiencies may not manufacture enough insulin to handle simple sugars (glucose), which may contribute to the development of diabetes.
• Vitamin D appears to be involved in the growth of cells essential to the body’s immune system.

Signs of Vitamin D Deficiency

Vitamin D deficiencies are relatively common. Rickets, primarily a childhood disease, is the most widely acknowledged disorder associated with this type of deficiency. A similar condition in adults, called osteomalacia, involves the same kind of softening of the bones; it is produced by inadequate calcification—that is, by a lack of sufficient calcium in the bones.

Children with rickets often lose their appetite and grow slowly. Their muscles may be weak, and their weight-bearing bones may buckle, resulting in bowed legs and spinal deformities. Swollen joints, bone pain and tenderness, and delayed tooth eruption may also occur, as well as a greater susceptibility to tooth decay. Adults with osteomalacia may have some of the same symptoms, as well as bone fractures.

Vitamin D Toxicity

Can your body manufacture too much vitamin D if you spend a lot of time in the sun? The simple answer is no. While overexposure to the sun will dramatically raise your risk of developing skin cancer, it won’t make you susceptible to toxic amounts of vitamin D. When your body has produced enough of that vitamin, a feedback system will automatically cut back the manufacturing process.

What about vitamin D supplements? Too much vitamin D taken this way can be toxic. This is because vitamin D is fat-soluble, so your body will retain excessive amounts rather than excrete them. Excessive amounts can persist in the body for weeks and even months.

In infants, doses as low as 1,800 IU per day can be toxic. In adults, symptoms of toxicity generally don’t appear until much higher intake levels are reached—about 50,000 IU per day. Because young children can overdose at much lower levels than adults, be cautious about giving supplements to youngsters. Before giving your child vitamin D supplements, check with your pediatrician or family doctor. Some doctors do advise giving a supplement of up to 400 IU of vitamin D per day to breast-fed babies or babies fed formula not fortified with vitamin D. Pediatricians also sometimes suggest supplements for older children—particularly those who don’t drink milk.

When There’s Too Little Sun

Because the skin can manufacture vitamin D when it is exposed to sunlight, you may not require any vitamin D in your diet. Don’t ignore dietary vitamin D completely, however, without thinking about your particular situation. How much time do you spend in the sun? How much of your skin is actually exposed to the sun? Do any environmental conditions smog, fog, sunscreen, or window glass—keep ultraviolet light from reaching your skin? These are important factors in determining whether your body can produce all the vitamin D it needs.

If you’re an older person, your skin produces vitamin D at about half the rate of the skin of a younger person. Skin pigment is important, too: to produce the same amount of vitamin D, people with dark skin require more sun exposure than people with light skin. The bodies of people living further from the equator also take longer to produce vitamin D.

Researchers use complicated formulas to calculate how fast your body manufactures vitamin D. These formulas need adjustment depending on the time of year and other factors, including those described here. In general, though, you need more than two hours of facial exposure per day in the winter months to meet your body’s requirements, and less in the summer.

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