What Is Vitamin D? What Are The Benefits Of Vitamin D?

Editor's Choice
Main Category: Nutrition / Diet
Also Included In: Dermatology;  Public Health
Article Date: 24 Aug 2009 - 1:00 PDT

email icon email to a friend   printer icon printer friendly   write icon opinions  


Current Article Ratings:

Patient / Public:4 stars

3.99 (722 votes)

Healthcare Prof:4 stars

3.81 (134 votes)

Article Opinions: 59 posts

Vitamin D is a steroid vitamin, a group of fat-soluble prohormones, which encourages the absorption and metabolism of calcium and phosphorous. People who are exposed to normal quantities of sunlight do not need vitamin D supplements because sunlight promotes sufficient vitamin D synthesis in the skin.

Five forms of vitamin D have been discovered, vitamin D1, D2, D3, D4, D5. The two forms that seem to matter to humans the most are vitamins D2 (ergocalciferol) and D3 (cholecalciferol).

Researchers at the University of Minnesota found that Vitamin D levels in the body at the start of a low-calorie diet predict weight loss success, suggesting a possible role for vitamin D in weight loss.

Data collected from the National Health and Nutrition Examination Survey (NHANES), USA found that 9% (7.6 million) of children across the USA, was vitamin D deficient (defined as less than 15 ng/mL of blood), while another 61 percent, or 50.8 million, was vitamin D insufficient (15 to 29 ng/mL) (reference "We expected the prevalence of vitamin D deficiency would be high, but the magnitude of the problem nationwide was shocking," says lead author Juhi Kumar, M.D., M.P.H., a fellow in pediatrics at Children's Hospital at Montefiore Medical Center, The University Hospital and Academic Medical Center for Albert Einstein College of Medicine.

Vitamin D - sunlight through leaves
Vitamin D for humans is obtained from sun exposure, food and supplements. It is biologically inert and has to undergo two hydroxylation reactions to become active in the body. The active form of vitamin D in the body is called Calcitriol (1,25-Dihydroxycholecalciferol).

Calcitriol promotes the absorption of calcium and phosphorus from food in the gut and reabsorption of calcium in the kidneys - this increases the flow of calcium in the bloodstream. This is essential for the normal mineralization of bone and preventing hypocalcemic tetany. Hypocalcemic tetany is a low calcium condition in which the patient has overactive neurological reflexes, spasms of the hands and feet, cramps and spasms of the voice box (larynx). Calcitriol also plays a key role in the maintenance of many organ systems.

Various forms of vitamin D

We know about 5 forms of vitamin D, of which vitamins D2 and D3 are the major forms as far as humans are concerned. They are known collectively as calciferol.

Which is more important for humans, vitamins D2 or D3?

Both vitamins D2 and D3 are used in human nutritional supplements. Pharmaceutical forms include calcitriol (1alpha, 25-dihydroxycholecalciferol), doxercalciferol and calcipotriene. The majority of scientists state that D2 and D3 are equally effective in our bloodstream. However, some say that D3 is more effective. Animal experiments, specifically on rats, indicate that D2 is more effective than D3.

What do we need vitamin D for?

Sunlight and vitamin D requirements

If you live in the tropics and can expose your unprotected skin to two sessions of 15 minutes of sunlight each week your body will naturally produce adequate amounts of vitamin D. The following factors may reduce your body's vitamin D synthesis: If your body cannot produce enough vitamin D because of insufficient sunlight exposure you will need to obtain it from foods and perhaps supplements. Experts say that people with a high risk of vitamin D deficiency should consume 25 μg (1000 IU) of vitamin D each day so that there is a good level of 25-hydroxyvitamin D in the bloodstream. Elderly people, as well as people with dark skin should consume extra vitamin D for good health.

How much vitamin D do I need?

The information below relates to people who do not have exposure to sunlight.

According to the Food Nutrition Board at the Institute of Medicine of The National Academies, which created the Dietary Reference Intakes (DRIs), people should be intaking the following amounts of vitamin D if nothing is being synthesized (no sunlight exposure): The American Academy of Pediatrics recommends that exclusively or partially breastfed babies should receive supplements of 400 UI per day shortly after birth, and when they are weaned they should consume a minimum of 1,000 mL/day of vitamin D fortified formula or whole milk. Non-breastfed infants consuming less than 1,000 mL/day of vitamin D-fortified formula or milk should receive a vitamin D supplement of 400 IU per day. It also recommends that older children and adolescents who do not get 400 IU per day through vitamin D fortified milk and foods should take a 400 IU vitamin supplement each day.

Vitamin D and nutrition

Vitamins as part of diet
Over the last few hundred years human lifestyles have changed. The industrial revolution resulted in more indoor work and less exposure to sunlight. Many societies around the world wore more clothing over the centuries, further reducing skin exposure to sunlight. These changes have brought with them a significant reduction in the natural production of vitamin D and subsequent diseases.

Countries responded to these changes by fortifying some foods with vitamins D2 and D3, examples include breakfast cereals, bread, pastries, oil spreads, margarine, milk and other dairy products. Initially, some scientists complained that nutritional fortification and recommended supplementation doses were not making up for the shortfall. These people were ignored, and sometimes ridiculed - however, over the last few years studies indicate that they may have been right after all.

Not that many foods contain vitamin D. Some fish, such as salmon, tuna and mackerel, as well as fish liver oils are considered to be the best sources. Some vitamin D is also present in beef liver, cheese and egg yolks. Most of these are Vitamin D3. Some mushrooms provide variable amounts of vitamin D2.

Most of the food sourced vitamin D in the western diet comes from fortified foods - where vitamin D is artificially added. Most US milk is fortified with 100 IU/cup of vitamin D. In the 1930s milk was fortified in many countries to combat rickets, which was a major health problem then.

Written by Christian Nordqvist
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

Visit our nutrition / diet section for the latest news on this subject.
There are no references listed for this article.
Please use one of the following formats to cite this article in your essay, paper or report:

MLA
Christian Nordqvist. "What Is Vitamin D? What Are The Benefits Of Vitamin D?." Medical News Today. MediLexicon, Intl., 24 Aug. 2009. Web.
3 Feb. 2012. <http://www.medicalnewstoday.com/articles/161618.php>

APA
Christian Nordqvist. (2009, August 24). "What Is Vitamin D? What Are The Benefits Of Vitamin D?." Medical News Today. Retrieved from
http://www.medicalnewstoday.com/articles/161618.php.

Please note: If no author information is provided, the source is cited instead.


Nutrition / Diet

Healthy Restaurant Eating: Is The Tide Turning In Fast Foods?

Eating out, and the amount we spend on it, especially on fast foods, has been rising steadily for decades, and parallels the increase in daily calorie intake that is contributing to the growing obesity crisis. But is that about to change? Read more...

Most Popular Articles



Follow Our Nutrition News On Twitter

Follow Us On Twitter
Get the latest news for this category delivered straight to your Twitter account. Simply visit our Nutrition / Diet Twitter account and select the 'follow' option.



View list of all 'What Is...' articles »