Vitamin D deficiency

What is vitamin D and why does it matter?

Vitamin D is a fat-soluble vitamin. In the body it:

• ensures the absorption of dietary calcium and phosphorus from the intestine;
• prevents excessive secretion of parathyroid hormone, which leads to bone loss;
• maintains the balance of calcium and phosphorus in the body;
• has a positive effect on the immune system;
• has a protective effect against hypertension, heart disease and some cancers and autoimmune diseases.

Where does vitamin D come from?

Vitamin D is mainly produced in the skin under the influence of sunlight. Spending about 20 minutes in the sun every day with the face, arms and legs uncovered can meet the daily requirement. The amount of sun needed depends on skin colour, age and other medical conditions. Skin production declines with age, and people with dark skin need longer sun exposure, especially in winter. Sunscreen with SPF 20 or higher prevents vitamin D formation in the skin.

In some countries milk and dairy products, bread and cereals are fortified with vitamin D; in Azerbaijan this is not yet practised. Vitamin D is naturally found in:

• oily sea fish (salmon, tuna) and fish oil;
• eggs (especially the yolk) and caviar;
• butter, milk, oats, liver;
• some types of mushrooms, parsley and alfalfa.

Causes of deficiency

• Insufficient intake from sunlight and food. This is more common in infants, children and older adults: breast milk contains very little vitamin D, older people often avoid dairy products and oily fish because of dietary restrictions, and their intestinal absorption also declines. People who are overweight, have dark skin, or live in northern regions or through long winters are also at risk.
• Impaired intestinal absorption: coeliac disease, Crohn’s disease, cystic fibrosis, removal of part of the stomach or intestine, and gastric bypass surgery for obesity.
• Liver and kidney disease: in chronic liver or kidney failure, the enzymes that convert vitamin D into its active form are insufficient.
• Certain medicines: corticosteroids impair calcium absorption and vitamin D metabolism; orlistat and cholestyramine reduce its intestinal absorption; the antiepileptic drugs phenobarbital and phenytoin reduce its activation in the liver.
• Some hereditary (familial) disorders.

Consequences of deficiency

Vitamin D insufficiency (a moderately low level) usually causes no noticeable symptoms. Even so, timely detection and treatment are very important for bone and muscle health. Deficiency can lead to:

• low blood calcium (hypocalcaemia);
• low blood phosphorus (hypophosphataemia);
• softening and bending of the bones in children (rickets);
• softening of the bones and muscle weakness in adults (osteomalacia);
• reduced bone mass and more frequent fractures (osteoporosis).

Diagnosis: who needs testing?

The diagnosis is based on the blood level of vitamin D (25(OH)D): above 30 ng/ml — normal; 20–30 ng/ml — vitamin D insufficiency; below 20 ng/ml — vitamin D deficiency.

The test is expensive and should not be done routinely for everyone. Checking the level is advisable for:

• bedridden or housebound people;
• people with a condition that can cause vitamin D deficiency;
• people with osteoporosis;
• people who have had a fracture after minor trauma (for example, a fall from standing height);
• people with low blood calcium (hypocalcaemia) or phosphorus (hypophosphataemia);
• people taking medicines that affect vitamin D metabolism.

Treatment

Deficiency is treated with vitamin D preparations. Pharmacies sell vitamin D alone, combined with calcium, or as part of multivitamins, in the form of drops, syrup, dragées, capsules, chewable and soluble tablets, and ampoules. If intestinal absorption is impaired, vitamin D is given by injection.

The dose is chosen individually, depending on how low the vitamin D level is and on its cause, so it should be decided together with your doctor.

Calcium should be taken alongside vitamin D treatment: 1000 mg a day at age 31–50 and 1200 mg a day over 51. Calcium can come both from food and from combined vitamin D preparations.

Taking too much vitamin D can cause toxicity: blood calcium rises (hypercalcaemia), leading to related health problems. To prevent this, read the medicine leaflet carefully and do not take several vitamin D-containing products at the same time (for example, a multivitamin together with a vitamin D preparation).

Prevention

The daily vitamin D requirement depends on skin colour, sun exposure, diet and the presence of other diseases.

For adequate vitamin D production in the skin, the face, neck, arms and legs should be exposed to sunlight without sunscreen for 2–30 minutes at least twice a week, outside the hours of 10:00–15:00. Smog, air polluted by industrial smoke and car exhaust, and covering clothing reduce vitamin D synthesis.

In adults, 400–800 IU is usually enough to maintain a normal vitamin D level. Most multivitamins for infants and children contain added vitamin D; in Azerbaijan, vitamin D for infants is available as drops, which is the most suitable form for children.