Vitamin D

Dr. Parang Mehta, MD.

Vitamin D has always been considered an important vitamin, because of its role in bone formation and calcium metabolism. In recent years, it has gained more attention because of its role in many long term diseases like heart disease, diabetes and cancer.

The main role of vitamin D is to increase the absorption of calcium and phosphorus from the small intestine. It also regulates an enzyme, alkaline phosphatase, which is important in the deposition of calcium and phosphorus in bones and teeth.

Sources of Vitamin D

A mostly indoors lifestyle does not permit the body to make enough vitamin D

Vitamin D is synthesised in the body from cholesterol, on exposure to sunlight. Inadequate outdoor activities and poor exposure to sunlight can lead to deficiency of vitamin D. The vitamin D so formed is activated in the liver. Liver disorders can also lead to manifestations of vitamin D deficiency.

The vitamin is also found in fish and fish liver oil, and fortified margarine and milk. Dairy products are poor sources of vitamin D, as is breast milk.

Vitamin D Deficiency

In growing children, it manifests as rickets, a disorder of growing bones. In the absence of adequate levels on calcium, bone formation is deranged. The wrists and ankles are widened, the ribs are depressed, the joints of the ribs are beaded (the "rachitic rosary"), and the bones are bent. The spine may also be bent, the skull is softened, and the abdomen is soft and large. Not all these can be reversed by vitamin D treatment, and hence, attention to intake from an early age is important.

Vitamin D - Other Effects

People with low levels of vitamin D have a higher incidence of respiratory infections, chronic obstructive pulmonary disease and tuberculosis. Children of women who had insufficient vitamin D are at higher then normal risk for asthma and other respiratory disorders.

Low vitamin D levels are also associated with hypertension, cancer, and cardiovascular diseases. Both the onset and progression of diabetes mellitus have been linked to levels of vitamin D. Chronic kidney disease is also made worse by deficiency of this vitamin.

Most of these effects of vitamin D are known from observational studies. More rigorous studies of these associations are needed. We also need to know whether raising the blood vitamin levels has a beneficial effect, and what levels are best.

Vitamin D Requirements

Recommended Dietary Allowances for normal children:

0-12 months: 400 IU (10 micrograms) per day.
1-18 years: 600 IU (15 micrograms) per day.

Vitamin D Testing

Measurement of 25-hydroxyvitamin D (25[OH]D) levels in the blood is one way to diagnose deficiency. Levels below 30 nanograms per mL signify insufficiency, levels below 10-20 nanograms per mL signify deficiency of vitamin D.

Treatment of Vitamin D Deficiency

Exposure to sunlight can probably reverse vitamin D deficiency, but oral treatment is better.
Daily dose of 2000 International Units (IU) of vitamin D for 6 weeks or
Weekly dose of 50,000 IU of vitamin D for 6 weeks.

When the serum 25(OH)D level crosses 30 ng/mL, switch to maintenance treatment of 400-1000 IU/day.

 

Last Revision: May 14, 2020