How Vitamin D Works


With an ample amount of sunlight, you can actually create vitamin D -- which has helped decrease risk of vitamin D-deficiency diseases such as rickets and osteomalacia in areas with frequent sunny days. But there's more to this very cheery vitamin than meets the eye. Vitamin D helps the body absorb calcium, and without it, bones are weakened. However, too much vitamin D can be toxic, especially in children. In this article, we'll discuss the importance and amounts needed of vitamin D. Here's a brief overview:
  • What is Vitamin D?

    Your body can make its own vitamin D with enough sunlight -- which researchers discovered when it became clear vitamin D-deficiency diseases such as rickets were rare in sunny climates. In the 1920s, rickets was prevented by feeding children cod liver oil or foods exposed to ultraviolet light. Today rickets is rare in the United States because milk is now fortified with vitamin D. Learn about vitamin D's history.
  • Benefits of Vitamin D

    Vitamin D is needed to help the body absorb calcium and phosphorus, which help growth of bones and teeth. In addition, vitamin D regulates whether these minerals are deposited into bone or withdrawn out of it. If minerals are drawn out more than they are put in, this can leave bones soft and weak. On this page, we'll discuss more about vitamin D's uses.
  • Foods That Contain Vitamin D

    The foods that contain significant amounts of vitamin D naturally are not necessarily foods you want to overdo: butter, cream, egg yolks and liver. However, all milk -- including skim -- is fortified with vitamin D and is an excellent source. Learn more about what foods are vitamin D sources.
  • Vitamin D Deficiency

    Vitamin D deficiency causes rickets, or bone softening, in children, and in adults can cause osteomalacia, which involves the loss of calcium and protein from bones. Though rickets is rare in the United States today, some cases do appear in low-income and vegetarian children and infants breast-fed for an extended period of time with no supplementation. Find out more about Vitamin D deficiency in this section.
  • Vitamin D Supplements

    Adding extra vitamin D to a diet can be helpful for vegans, babies who are breastfed and people with rickets. However, too much vitamin D can be toxic, resulting in calcium deposits in the kidneys, heart and other tissues that causes irreversible damage, and therefore amounts should be carefully regulated. Check out this section for more on what supplements exist and how much is needed.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

What Is Vitamin D?

Vitamin D is often called the sunshine vitamin -- and for good reason. If you get enough sunshine, your body can make its own vitamin D, which is important because Vitamin D provides a number of health benefits. But Vitamin D's positive effects weren't always recognized.

Years ago, very few children in tropical countries developed the malformed bones and teeth characteristic of rickets. Yet many children in temperate climates and large industrial cities did. Why the difference? The sun.

Vitamin D can be created naturally with sunlight.
©2007 Publications International, Ltd.
The human body can make vitamin D naturally with enough exposure to sun.

Skin contains a cholesterol substance called provitamin D, which starts to convert to vitamin D when exposed to sunlight. In tropical countries, sunlight shone on children year-round. Since these children had ample opportunity for exposure, their skin formed adequate amounts of vitamin D and thus they didn't experience the symptoms of rickets.

Children in temperate zones, however, got little exposure to the sun during the winter months, and their skin could not make enough vitamin D. Neither could the skin of children in large, industrial cities because the smoke-filled air filtered out much of the sun's ultraviolet light.

At one time, rickets afflicted large numbers of children in this country as well. Researchers found that the cause was that there was something preventing calcium from being deposited in the bones of these children-some substance that promoted calcium deposition was missing. From this research, investigators concluded that rickets was actually a vitamin-deficiency disease.

However, researchers were perplexed when they discovered that ultraviolet light could also prevent the deficiency. In the 1920s, nutritionists were able to prevent or cure rickets by feeding children cod liver oil or foods exposed to ultraviolet light. They also prevented rickets by exposing children to direct sunlight or the light from a sunlamp.

The explanation for these findings didn't crystallize for several more years. Cod liver oil was effective against rickets because it contains vitamin D. Foods exposed to ultraviolet light were effective because the light changed a substance in plant foods into a form of the vitamin -- vitamin D2.

Today, doctors seldom see cases of rickets in the United States. The few cases that do occur can usually be traced to poverty, neglect, or ignorance. The dramatic drop in rickets cases is primarily due to the increased availability of milk fortified with vitamin D. Choosing to fortify milk made sense because children usually drink lots of it. It's also the single best source of calcium in the American diet, and since vitamin D helps the body use calcium to build strong teeth and bones, milk was the best food to select.

Functions of Vitamin D

Vitamin D is necessary to help the body absorb the minerals calcium and phosphorus, which are needed for the proper growth and development of bones and teeth. It also regulates whether these minerals are deposited into bone or withdrawn out of bone to meet other needs. If minerals are drawn out more than they are put in, this can leave bones soft and weak. Vitamin D signals the kidneys whether to release calcium and phosphorus when the body has plenty or hold onto them when the body is running short.

Whether it comes from food or is made in the skin, vitamin D must be activated before it can be used. It first travels to the liver, where it undergoes a chemical change. Then it moves through the bloodstream to the kidneys, where it undergoes another change to become the active form of the vitamin. This active form -- dihydroxy vitamin D -- is the one that functions.

Society has recognized the importance of Vitamin D over time; but what are the central reasons for making sure you are getting enough Vitamin D? In the next section, we'll discuss the reasons this vitamin is so crucial.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

Benefits of Vitamin D

Vitamin D has a number of important uses -- important enough, in fact, to inspire the United States to fortify milk with it in order to prevent diseases like rickets. There are a number of ways Vitamin D works once it enters the body, and a number of ways it helps regulate bodily functions and assists in nutrient absorption.

Research shows that many types of cancer cells have places on them for the active form of vitamin D to bind. When vitamin D binds there, replication of the cancer cells slows down. But because excess vitamin D is very toxic, it's difficult to use vitamin D therapeutically to treat cancer, except in research settings.

However, having some sun exposure daily to keep vitamin D levels up has been shown to reduce the risk for colon cancer. Just don't overdo the tanning -- skin cancer is strongly associated with sunburn!

Vitamin D helps build strong bones.
©2007 Publications International, Ltd.
Vitamin D regulates whether minerals are deposited into bones or withdrawn
from them, preventing soft or weak bones.

Vitamin D is helpful in preventing osteoporosis. When given along with calcium supplements, vitamin D is able to signal the bones to hold onto their calcium rather than release it.

Vitamin D may also play a role in protecting people from
multiple sclerosis. This disease is so much more common in northern climates that researchers are studying whether vitamin D deficiency increases the risk for developing this disease.

Topically applied, vitamin D may be helpful for psoriasis by limiting the growth of abnormal skin cells. Topical vitamin D for psoriasis is available only by prescription and can be quite expensive.
Other uses for vitamin D include reducing the symptoms of some forms of
arthritis and maybe even helping to reduce the risk for insulin-dependent diabetes in young children.

If you're not getting enough vitamin D daily, you can increase your intake through taking supplements. In the next section, we'll discuss what types of supplements exist and how to know if you need to up your vitamin D dosage.

While sunlight is one way to obtain vitamin D, it's not the only way. Many foods contain vitamin D -- some, such as milk, have even been fortified with it. In the next section, we'll learn which foods are the best sources of vitamin D.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

Foods That Contain Vitamin D

It's clear vitamin D is important -- but how do you get it? It's true that vitamin D can be produced naturally via sunlight, but it is also in some common foods. However, some foods are better sources of vitamin D than others.

Few foods contain significant amounts of vitamin D naturally, and the ones that do are not foods you want to overdo: butter, cream, egg yolks, and liver. But there are some good sources. All milk -- including skim milk -- is fortified with vitamin D at a level of 100 IU per cup. Some manufacturers also fortify cereals with vitamin D. Cod liver oil, as a supplement, contains about 1,200 IU of vitamin D per tablespoon. Cod liver oil should be used cautiously as a dietary supplement, however, because it also contains high levels of vitamin A -- that can have toxic effects.

Eggs contain Vitamin D.
©2007 Publications International, Ltd.
Egg yolks are a source of Vitamin D,
but aren't a food that is healthy to
eat in excess.

A fair-skinned person can make a sufficient quantity of vitamin D with only 20 to 30 minutes of sun exposure a day. It would take much more time, about three hours, for a dark-skinned person to make an equal amount of the vitamin because skin pigment filters out UV rays.

You cannot overdose on vitamin D from sun exposure because it limits itself. Of course, you can get too much sun, increasing your risk of skin cancer. Unfortunately, because sunscreens filter out the ultraviolet rays that burn your skin, they block the manufacture of vitamin D as well. Exposing unprotected skin to the sun in the early morning or late afternoon hours solves both problems.

Clouds, smog, clothing, and even window glass also filter out ultraviolet rays. Housebound people, those with dark skin, those that cover most of their skin when outdoors and those who live in cloudy, northern climates are most likely to be deficient in vitamin D. These people must get vitamin D from foods.

Here is a chart you can use to find foods rich in vitamin D:

Sources of Vitamin D
Food Quantity
Vitamin D (mcg)
Tuna salad
1 cup
7.5
Skim milk
1 cup
2.5
Milk 1 cup
2.5
Egg substitute
1/2 cup
2.1
Eggnog 1/2 cup
1.5
Raisin Bran
1 cup
1.4
Total cereal
1 cup
1.2
Product 19
1 cup
1.2
Yogurt, low-fat
1 cup
1.2
Special K
1 cup
1.2

If you don't receive enough vitamin D, there are a number of deficiency issues that can arise. In the next section, we'll discuss the negative effect a lack of vitamin D can have on your bones and body overall.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

Vitamin D Deficiency

Although Vitamin D can be found in such everyday foods as milk, it's not always ingested at high enough amounts, resulting in a number of Vitamin D deficiency problems. These issues can include disorders such as rickets and osteomalacia.

Vitamin D deficiency in adults involves the loss of calcium and protein from bones.
©2007 Publications International, Ltd.
Vitamin D deficiency in adults involves the
loss of calcium and protein from bones.

Vitamin D deficiency causes rickets in children. Because vitamin D is crucial to proper calcium metabolism, the hallmark of rickets is the undermineralization and softening of bones. One of its common signs is bowlegs. Another sign is beadlike swellings on the ribs -- a condition called rachitic rosary. Teething is usually late in children with rickets, and what teeth do develop are susceptible to decay.

Though rickets is rare in the United States today, some cases do appear in low-income children, vegetarian children, infants who were breast-fed for an extended period of time with no supplementation, and in older adults who can no longer make vitamin D efficiently.

Vitamin D deficiency in adults results in a condition called osteomalacia. It involves the loss of calcium and protein from bones, due to insufficient vitamin D. Osteomalacia differs from osteoporosis in that bone loses only mineral. In osteoporosis, bone itself is lost. In developing countries, osteomalacia is prevalent in women who have low intakes of calcium and vitamin D, and several closely spaced pregnancies followed by long periods of breast-feeding.

If you're not getting enough vitamin D daily, you can increase your intake through taking supplements. In the next section, we'll discuss what types of supplements exist and how to know if you need to up your vitamin D dosage.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

Vitamin D Supplements

Everyone needs Vitamin D -- but how much? And if you're not getting it in your daily diet, how do you know where to go to get more Vitamin D? You can overdo Vitamin D, so caution is needed.

Vitamin D is actually the most toxic of all the vitamins. As little as ten times required amounts -- 50 mcg -- can be toxic to children. Symptoms of overdose include diarrhea, nausea, and headache. The most serious complication is the elevated blood calcium levels that too much vitamin D can cause. This condition can lead to calcium deposits in the kidneys, heart, and other tissues, causing irreversible damage .

Vitamin D supplements should not be taken in excess.
©2006 Publications International, Ltd.
Vitamin D supplements are often
recommended for babies being
breast fed and vegans.

Breast-fed babies routinely receive vitamin D supplements. Formula-fed infants, on the other hand, receive the recommended amount of vitamin D in commercial infant formula and do not require additional supplementation. Vegetarians who do not eat dairy or egg products or get enough sunlight should consider taking vitamin D supplements.

The standard treatment for rickets is a fairly high dose of vitamin D given under a doctor's supervision. Doctors give the active form when the conversion of vitamin D to the active dihydroxy form is inadequate, possibly due to liver or kidney disease.

Approximately 400 mcg daily is an appropriate amount for osteoporosis prevention.

Vitamin D is a crucial element of any healthy diet -- whether received by sun, or via food such as milk, which is now fortified with vitamin D or supplements, making sure you get enough is important. However, you can also take too much, which is dangerous. It's key to pay attention to where you are receiving Vitamin D from and how much you are getting and to watch for symptoms over vitamin D overdose, which include diarrhea, nausea, and headache.

In addition to Vitamin D, other supplements can be taken to improve diet. Some of these are listed below.
  • Vitamin E is an antioxidant in the cells and tissues of the body, combining with oxygen and destroying free radicals. Find out more about Vitamin E in How Vitamin E Works.
  • Vitamin B3 helps turn protein, carbohydrate and fat into energy. Learn more in How Vitamin B3 Works.
  • Vitamin K mostly affects the body's blood supply and the rate at which blood clots. How Vitamin K Works can tell you more about how this vitamin helps blood regulation in the body.
  • Folate functions as a coenzyme during many reactions in the body and has an important role in making new cells. Learn about this important element in How Folate Works.
  • Discovered only about 60 years ago, Biotin assists in several metabolic reactions. Learn more about it in How Biotin Works.
  • To learn about the many vitamins in our diet, how much you should be eating, and where to find them, go to our general Vitamins page.
ABOUT THE AUTHOR
Jennifer Brett, N.D. is director of the Acupuncture Institute for the University of Bridgeport, where she also serves on the faculty for the College of Naturopathic Medicine. A recognized leader in her field with an extensive background in treating a wide variety of disorders utilizing nutritional and botanical remedies, Dr. Brett has appeared on WABC TV (NYC) and on Good Morning America to discuss utilizing herbs for health.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.