Vitamin D

Description

Vitamin D is a hormone metabolized by the body and found in food. It is involved in maintaining adequate serum calcium and phosphate concentrations and plays a role in the formation of bones and teeth, muscle function and cell differentiation.

There are two forms of vitamin D: vitamin D2, found in plants, and vitamin D3, which is synthesized in the skin by exposure to sunlight.

Before they can be activated, vitamins D2 and D3 must first be transformed in the liver, then the kidneys.

Sources

Exposure to sunlight is the primary source of vitamin D. Between April and October, it is recommended that individuals expose their face and arms to sunlight, without sunscreen, for 10 to 15 minutes, between 11 a.m. and 2 p.m., three times a week. Individuals with darker skin require longer exposure. Not all dermatologists are in agreement with this practice as they are fearful of an upsurge in skin cancer.

Meeting the daily requirements through diet alone is difficult since very few foods contain vitamin D, with the exception of fatty fish. Soy and rice beverages, liquid milk products and margarine are, however, fortified with vitamin D. Egg yolks also contain vitamin D but yogurt and cheese do not.

Recommended Dietary Allowance (RDA)

Health Canada is in charge of making recommendations with regards to the average daily dietary intake level for vitamin D and other vitamins. The intake is considered to be sufficient to meet the nutrient requirements of most healthy men and women (97 to 98%) in a particular age group and who follow a North American-type diet. These reference values are available on the Health Canada website, see Dietary Reference Intakes (DRIs).

Deficiency

Vitamin D stores in the body can last a few months. Vitamin D deficiency reduces calcium absorption, which can lead to bone fragility or deformation, convulsions, muscle weakness, rickets (poor development of bones in children) and tetany (unwanted muscle contractions).

Toxicity

Overexposure to the sun or dietary intake of vitamin D from food sources is unlikely to cause toxicity. When using vitamin D supplements, tests can be performed to measure serum levels of vitamin D, when indicated.

Vitamin D toxicity increases serum calcium concentrations and calcium loss through urine.

The first symptoms include itchiness, muscle weakness, headache, red eyes, drowsiness, nausea and vomiting, cardiac arrhythmia, excessive thirst, dry mouth, constipation, muscle and bone pain and a metallic taste.

Prolonged use of high doses of vitamin D may lead to increased urine output, loss of appetite, weight loss, calcification of the cornea, light sensitivity, runny nose, pancreatitis, increased temperature, decreased libido, hypercholesterolemia, kidney, lung, heart or ear drum calcification, kidney failure, hypertension, cardiac arrhythmia and on rare occasions, psychosis.

Supplements

Supplementation may be necessary. Needs may vary depending on the season, latitude, age and dietary intake. Health Canada recommends that everyone over the age of 50 take a daily vitamin D supplement. Vegetarians, those living in northern climates (such as Canada), and those who are institutionalized are at a greater risk for vitamin D deficiency.

To find out if you should take a supplement, speak to your pharmacist.

Watch what you eat. Nutrition has a significant impact on health!