Vitamin D
Recommended Intake
Vitamin D Deficiency
Vitamin D Toxicity
Major Food Sources
Vitamin D and Osteoporosis
Tips for Increasing Your Vitamin D Intake

Vitamin D is a fat-soluble vitamin. Fat-soluble vitamins are stored in the body in the liver and fatty tissues. Vitamin D acts as both a vitamin and a hormone.

Vitamin D is found in some foods, but the main sources are vitamin D-fortified milk and sunlight. The ultraviolet rays of the sun react with cholesterol present on the skin and create previtamin D3. This compound goes through a series of reactions involving the kidneys and the liver, and the final product is vitamin D.

Vitamin D's functions include:

• playing a crucial role in the growth and maintenance of strong, healthy bones
• maintaining normal blood levels of calcium and phosphorus

Recommended Intake

Vitamin D Deficiency
Symptoms of vitamin D deficiency include:

• rickets - in children, a disease in which the bones become soft and weak
• osteomalacia - in adults, a disease in which the bones become soft and weak
• muscle weakness

The following populations may be at risk for vitamin D deficiency and may require a supplement:

• Adults 65 and older. Studies have shown that adults over age 65 have roughly a fourfold decrease in the skin's ability to synthesize vitamin D from sunlight when compared with adults age 20 to 30.
• People with limited sun exposure. People who live above latitudes of approximately 40° N and below latitudes of approximately 40° S are at risk for deficiency during most of the winter months.
• People with a reduced ability to absorb dietary fat. Because vitamin D is a fat-soluble vitamin, fat is required for its absorption. Some conditions that can cause fat malabsorption include Crohn's disease, cystic fibrosis, celiac disease, pancreatic enzyme deficiency, and liver disease.

Vitamin D Toxicity
Since vitamin D is stored in the body, and not excreted in the urine like most water-soluble vitamins, it is possible for it to accumulate and reach toxic levels. The tolerable upper intake level (UL) for vitamin D from dietary sources and supplements combined is 2,000 IU. Symptoms of toxicity include:

• nausea
• vomiting
• poor appetite
• constipation
• weakness
• weight loss
• high blood pressure
• raised levels of calcium in the blood, which can cause:

  confusion
  heart rhythm abnormalities
  deposits of calcium in soft tissues, like the kidney, heart, and lungs

Major Food Sources

Most people's bodies can manufacture enough vitamin D with 10 to 15 minutes of sun exposure two to three times per week. However, this synthesis is affected by season, latitude, time of day, cloud cover, smog, and skin pigmentation.

Vitamin D and Osteoporosis
Osteoporosis is a disease in which bones become weak and brittle and are more susceptible to fracture. The hip, wrist, and vertebrae are common sites of fractures. Advancing age and being female are two key risk factors for developing osteoporosis.

Vitamin D deficiency has been associated with a greater incidence of hip fracture. And increased intakes of vitamin D have been associated with less bone loss in older women. This has led some researchers to believe that vitamin D supplementation may help prevent fractures resulting from osteoporosis.

Tips for Increasing Your Vitamin D Intake
To help increase your intake of vitamin D:

• If you take a vitamin supplement, make sure it contains vitamin D.
• Drink vitamin D-fortified milk.
• Get sun exposure, but be careful to watch for sunburn. Sunlight is a major cause of skin cancer.