Vitamin D deficiency

Definition

Vitamin D deficiency exists when the concentration of 25-hydroxy-vitamin D (25-OH-D) in the blood serum occurs at 12 nanograms/milliliter (ng/ml) or less. This is one-half to one-fourth the amount normally present. When vitamin D deficiency continues for many months in growing children, the disease commonly referred to as rickets occurs.

Description

Vitamin D is a fat-soluble vitamin, meaning it can be dissolved in fat. While some vitamin D is supplied by the diet, most of it is made in the body. To make vitamin D, cholesterol, a substance widely distributed in animal tissues, the yolk of eggs, and various oils and fats, is necessary. Once cholesterol enters the body, a slight alteration in the cholesterol molecule occurs, with one change taking place in the skin. This alteration requires ultraviolet light, a component of sunlight. Vitamin D deficiency and rickets tend to occur in children who do not get enough sunlight and who do not eat foods that are rich in vitamin D.

Once consumed or made in the body, vitamin D is further altered to produce a substance called 1,25-dihydroxy-vitamin D (1,25-diOH-D). The conversion of vitamin D to 1,25-diOH-D occurs in the liver and kidney. The role of 1,25-diOH-D in the body is to keep the concentration of calcium at a constant level in the bloodstream. Maintaining calcium at a constant level is absolutely required for human life, since dissolved calcium is required for nerves and muscles to work. One of the ways in which 1,25-diOH-D accomplishes this is by stimulating the absorption of dietary calcium by the intestines.

The sequence of events that can lead to vitamin D deficiency and later to bone disease, is as follows: a lack of vitamin D in the body creates an inability to manufacture 1,25-diOH-D. This results in decreased absorption of dietary calcium and an increased loss of calcium in the feces. When this happens, the bones are affected. Vitamin D deficiency results in a lack of bone mineralization (calcification) in growing children.

Demographics

Vitamin D deficiency is not common in the United States and other industrialized countries because of the wide availability of vitamin D fortified infant formulas and milks. It is somewhat more common in northern areas where there is not as much sunlight present during many parts of the year. Vitamin D deficiency is also slightly more common in inner city areas, because environmental factors, such as smog, can block the necessary ultraviolet (UV) component of sunlight. Children with darkly pigmented skin are more likely to be vitamin D deficient than light skinned children. Children who are exclusively breast-fed without vitamin D supplementation, particularly if they are not exposed to sunlight, are at higher risk of vitamin D deficiency.

Causes and symptoms

Vitamin D deficiency can be caused by conditions that result in little exposure to sunlight. These conditions include: living in northern regions, having dark skin, and having little chance to go outside. Children whose faces and bodies remain covered when outside can develop vitamin D deficiency even while living in a sunny climate. In-born errors of vitamin D metabolism can also cause vitamin D deficiency and rickets; these children cannot convert inactive vitamin D to active vitamin D and suffer the same symptoms as children with a nutritional deficiency.

Most foods contain little or no vitamin D. As a result, sunshine is often a deciding factor in whether vitamin D deficiency occurs. Although fortified milk and fortified infant formula contain high levels of vitamin D, human breast milk is rather low in the vitamin. (The term fortified means that vitamins are added to the food by the manufacturer.)

The Recommended Dietary Allowance (RDA) of vitamin D for both children and adults is 200 International Units (IU) per day. Saltwater fish such as salmon, herring, and sardines are naturally rich in vitamin D. Vitamin D fortified milk contains 400 IU per quart (liter), so half a quart (liter) of milk provides the RDA. For comparison, human breast milk contains only 4 to 60 IU per quart.

No harm is likely to result from vitamin D deficiency that occurs only a few days a year. If the deficiency occurs for a period of many months or years, however, rickets may develop. The symptoms of rickets include bowed legs and bowed arms. The bowed appearance is due to the softening of bones, and their bending if the bones are weight-bearing. Bone growth occurs through the creation of new cartilage, a soft substance at the ends of bones. When the mineral calcium phosphate is deposited onto the cartilage, a hard structure is created. In vitamin D deficiency, though, calcium is not available to create hardened bone, and the result is soft bone. Other symptoms of rickets include bony bumps on the ribs called rachitic rosary (beadlike prominences at the junction of the ribs with their cartilages) and knock-knees. Seizures may also occasionally occur in a child with rickets, because of reduced levels of dissolved calcium in the bloodstream.

When to call the doctor

The doctor should be called if the parent notices that the child has any signs of vitamin D deficiency or rickets. Such signs include skeletal pain , bowed limbs, and impaired growth. If there are lifestyle factors that make the child at risk for vitamin D deficiency, such as low milk or formula intake, a doctor should be consulted about the possibility of using vitamin D supplements.

Diagnosis

Vitamin D deficiency is diagnosed by measuring the level of 25-hydroxy-vitamin D in the blood serum. The

normal concentration of this form of vitamin D ranges from 25 to 50 ng/ml. Deficiency occurs when this level decreases to about 12 ng/ml or less.

Rickets is diagnosed by x-ray examination of the leg bones. A distinct pattern of irregularities, abnormalities, and a coarse appearance can be clearly seen if a child has rickets. Measurements of blood plasma 25-OH-D, blood plasma calcium, and blood plasma parathyroid hormone must also be obtained for the diagnosis of this disease. Parathyroid hormone and 1,25-diOH-D work together in the body to regulate the levels of calcium in the blood.

Treatment

Rickets heals promptly with large doses vitamin D administered orally each day for approximately one month. During this treatment, the doctor should monitor the levels of 25-OH-D in the plasma to make sure that they are raised to a normal level. The bone abnormalities (visible by x ray) generally disappear gradually over a period of three to nine months. Parents are instructed to take their infants outdoors for approximately 20 minutes per day with their faces exposed. Children should be encouraged to play outside and to eat foods that are good sources of vitamin D. These foods include cod liver oil, egg yolks, butter, oily fish and also foods, including milk and breakfast cereals, that are fortified with synthetic vitamin D.

Care must be taken in treating vitamin D deficiency, since high doses of vitamin D are toxic (poisonous) and can result in the permanent deposit of minerals in the heart, lungs, and kidneys. Symptoms of toxicity are nausea , vomiting , pain in the joints, and lack of interest in eating food. In adults, vitamin D toxicity occurs with eating 50,000 IU or more per day. In infants, toxicity occurs with 1,000 IU per day. The continued intake of toxic doses results in death.

Rickets are usually treated with oral supplements of vitamin D, with the recommendation to acquire daily exposure to direct sunlight. An alternative to sunlight is the use of an ultraviolet lamp. When people use UV lamps, they need to cover their eyes to protect them against damage. Many types of sunglasses allow UV light to pass through, so only those that are opaque to UV light should be used. Attempts to acquire sunlight through glass windows fail to help the body make vitamin D because UV light does not pass through window glass.

Rickets may also occur with calcium deficiency, even when a child is regularly exposed to sunshine. This type of rickets has been found in various parts of Africa. The bone deformities are similar to, or are the same as, those that occur in typical rickets; however, calcium deficiency rickets is treated by increasing the amount of calcium in the diet. No amount of vitamin D can cure the rickets of a child with a diet that is extremely low in calcium. For this reason, it is recommended that calcium be given in conjunction with vitamin D supplementation.

Prognosis

The prognosis for correcting vitamin D deficiency and rickets is excellent. Vitamin D treatment results in the return of bone mineralization to a normal rate, the correction of low plasma calcium levels, the prevention of seizures, and a recovery from bone pain. On the other hand, already established deformities such as bowed legs and the rachitic rosary persist throughout adult life.

Prevention

Vitamin D deficiency is a very preventable. Eating foods that are high in vitamin D or foods that have been fortified with additional vitamins in combination with getting moderate amounts of exposure to direct sunlight, are usually enough to prevent vitamin D deficiency.

Some authorities still recommend exposure to sunshine as a way to prevent vitamin D deficiency, but early exposure to direct sunlight may be linked to a higher incidence of skin cancer later in life, so other experts recommend that infants not be taken into direct sunlight without protective coverings or sunscreen until at least six months of age. These experts recommend that supplemental drops or fortified formulas instead of direct sunlight provide infants' daily requirements of Vitamin D. Children playing in the sunlight with sunscreen on is not an effective way for them to get vitamin D because the sunscreen inhibits its production in the skin.

Nutritional concerns

Vitamin D deficiency is caused by the child not getting enough vitamin D through nutrition and exposure to sunshine. Even after a case of vitamin D deficiency has successfully been resolved special care should be taken with the child's diet, as vitamin D deficiency can reoccur.

Parental concerns

Vitamin D deficiency can cause rickets, which can lead to permanently stunted or irregular growth. Vitamin D deficiency can usually be easily corrected if it is noticed early, and if so the symptoms often resolve themselves. However, negative effects such as short stature and pelvic deformations can be permanent.

Resources

BOOKS

Hochber, Ze'ev, ed. Vitamin D and Rickets. Farmington, CT: S. Karger, 2003.

PERIODICALS

Spence, Jean, T. and Janet R. Serwint. "Secondary Prevention of Vitamin D-Deficiency Rickets" Pediatrics 113 (January 2004): 129.

Wharton, Brian, and Nick Bishop. "Rickets." The Lancet 362 (October 2003): 1389.

Tish Davidson, A.M.