Sources of Vitamin D

Posted by Blog Friday, March 4, 2011

The natural source of vitamin D is from sunshine. As you may recall, just a few minutes of sun on the face and arms a few times a week will provide all the vitamin D that you need, except in high latitudes during winter. It is best to get in the sun even in the winter, although reserves of stored vitamin D normally last through the winter even without sufficient sun to make more.

There is no RDA for vitamin D. Instead, there is a daily Adequate Intake (AI).The AI for everyone under 50 years of age is 200 IU (5 mcg). Adults aged 51–70 have an AI of 400 IU (10 mcg) and for people over 70 the AI is 600 IU (15 mcg). These amounts are determined assuming that there is no vitamin D produced from sunlight. The AI is set to prevent rickets and osteomalacia.

Some experts recommend increased supplementation of vitamin D, while still staying well below the tolerable upper intake level (UL) of 2000 IU per day. These experts recommend an additional 200 IU on top of the AI, either from fortified foods, or from supplements. These higher levels may help to reduce the risk of osteoporosis and cancer.

Food sources of vitamin D are limited to a few fatty fish such as salmon, sardines, and mackerel. Some fish liver oils have high vitamin D content, but that is not the healthiest choice for vitamin D supplementation. Vitamin D is added to the feed of some laying hens to produce eggs with vitamin D. Some cereals, breads,and  orange juices are fortified with vitamin D. Check the labels to see if they are fortified.

Summary for Vitamin D

Main functions: keeps bones strong and helps regulate calcium and phosphorus.

Adequate Intake: under age 50: 200 IU. Ages 51–70:

400 IU. Age 70+: 600 IU.

Toxicity is possible only with supplemental forms of vitamin D and is rare.

Tolerable upper intake level is set at 2,000 IU daily.

Deficiency disease: rickets and osteomalacia (soft bones).

Healthy sources: sunshine. Supplementation with vitamin D3 may be needed.

Food sources: fortified milk, salmon, sardines, and mackerel.

Forms in the body: cholecalciferol, calcidiol, and calcitriol.

Milk is fortified with the addition of 400 IU of vitamin D2 to each quart in the United States. Other dairy products are not normally fortified. Margarine may befortified with Vitamin D.

Toxicity of Vitamin D

It is important to note that vitamin D created from sunlight on skin is not known to result in toxic levels. Levels of vitamin D produced from sunlight are self-adjusting. Vitamin D toxicity is known as hypervitaminosis D. Toxic levels of vitamin D can cause abnormally high blood calcium levels. This can result in bone loss and kidney stones. Long-term overconsumption of vitamin D can cause calcification of organs such as the heart, blood vessels, and the kidneys. Vitamin D toxicity is unlikely in healthy adults with supplement levels lower than 10,000 IU/day. The Food and Nutrition Board has established a very conservative tolerable upper intake level (UL) of 2,000 IU/day (50 mcg/day) for children and adults. The UL for infants up to one year of age is 1000 IU. To summarize, we need vitamin D to keep our bones strong. Vitamin D may play an anti-cancer role by slowing cell division. Sunshine is the natural source of vitamin D


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