All about Vitamin D

Vitamin D:

Vitamin D, calciferol, is a fat soluble vitamin. Fat soluble vitamins are stored in the body’s fatty tissue. Vitamin D is found in food but can also be made by your body following the exposure to UV rays from the sun. Vitamin D is present in different forms, and each form has a different activity. Some forms are relatively inactive and therefore have limited activity in the body. The kidney and liver convert the inactive form of vitamin D to the biological active forms.

What does vitamin D do?

Vitamin D’s primary role is to maintain normal blood levels of calcium and phosphorus. Vitamin D, in conjunction with other nutrients, helps maintain healthy bones. By aiding in the absorption of calcium, Vitamin D promotes mineralization. Without vitamin D bones become brittle and thin. Vitamin D helps prevent bone diseases that result in weakened bones such as rickets, in children, and osteomalacia in adults. Too much vitamin D may have the opposite effect of taking calcium from bones and depositing it in the heart or lungs which reduces their elasticity thereby reducing their function.

Vitamin D may also reduce the risk of cardiovascular disease, certain cancers, and Alzheimer's disease.

What are the sources of vitamin D?

Food Sources:
Fortified foods are the major dietary sources of vitamin D. Prior to fortification with vitamin D of milk products in the 1930’s, rickets disease was a major public health problem in the US. Milk fortification was set at 400 IU per quart (4 cups) of milk. Hence, 4 cups = dietary needs, 1 cup= ¼ dietary needs.

Here are some good dietary sources of vitamin D:

Food Source Serving Amount IU Content
1. Cod liver oil 1 tbs 1,360 IU
2. Salmon 3 ½ oz. 360 IU
3. Mackerel 3 ½ oz. 345 IU
4. Sardines 3 ½ oz. 270 IU

How much vitamin D do we need?

The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each life-stage and gender group. Unlike many other nutrients, there is insufficient evidence to establish an RDA for vitamin D. Instead, a level of intake sufficient to maintain healthy blood levels of an active form of vitamin D, Adequate Intake (AI), has been established. The 1998 AIs for vitamin D for adults are the same in males and females, but increase with age.

Ages 19-50: 200 International Units (IU)
Ages 51-69: 400 IU
Age 70 and older: 600 IU

When can vitamin deficiency occur?

Vitamin D deficiency can occur when there is an inadequate intake of dietary vitamin D or exposure to sunlight. Physiological problems such as if the kidney is unable to convert vitamin D to its active form or if the gastrointestinal track has an inadequate vitamin D absorption can also lead to vitamin D deficiency.

Who may need extra vitamin D to prevent deficiency?

People over 50 years of age may have a higher risk of developing vitamin D deficiency. As we age our ability to produce vitamin D from sunlight exposure and for the kidney to convert vitamin D to its active form is thought to decrease. Therefore, older people may need to take vitamin D supplements.

Additionally, people with limited sunlight exposure do to geographical location, seasonal limitations, health conditions, or for occupational reasons may also benefit from vitamin D supplementation.

People who have fat mal-absorption may also benefit from vitamin D supplementation. As previously mentioned, vitamin D is a fat soluble vitamin and therefore fat absorption plays a key role in vitamin D absorption. Some of the conditions that may result in fat mal-absorption include pancreatic enzyme deficiency, Crohn's disease, cystic fibrosis, liver disease, surgical removal of part or all of the stomach, and small bowel disease. Signs of fat mal-absorption include diarrhea, and greasy stool.

Furthermore, infants that are both breast-fed exclusively and are not exposed to the sun may benefit from vitamin D supplementation. Breast milk may not contain the needed amounts of vitamin D. However, according to the Institute of Medicine, infants with habitual small doses of sunshine do not need to take vitamin D supplements.

This blog is strictly for informational purposes. It is not intended to serve as clinical advice. If you have concerns about vitamin D status or supplementation, consult a physician prior to starting vitamin D supplementation.