Vitamin A Depletion & Osteoporosis

The International Osteoporosis Foundation estimates that 200 million women across the world suffer from osteoporosis and the National Osteoporosis Foundation reports that 12 million Americans over the age of 50 have the disease. While the exact cause of osteoporosis is not yet known, researchers believe that vitamin A intake may be a contributing factor. However, it isn't vitamin A depletion or deficiency that scientists think might help cause osteoporosis; rather, studies indicate that excessive intake of certain forms of vitamin A may significantly increase the risk of developing osteoporosis.

Osteoporosis

Osteoporosis is a condition in which the bones become weakened by the development of larger holes and spaces within the bones' basic structure. These holes make the bones more likely to break. A number of factors increase your risk of getting osteoporosis -- a family history of the condition, being physically inactive, smoking, excessive alcohol intake, consuming insufficient calcium, thinness and being female -- but scientists do not completely understand what triggers the changes in bone structure. Regular exercise and a diet high in both calcium and vitamin D can help prevent osteoporosis.

Vitamin A Effect on Osteoporosis

In 2000, a study published in "Nutrition Reviews" connected an increased risk of osteoporosis with excess vitamin A intake. Vitamin A is a compound that occurs in either retinol or provitamin A carotenoid forms and is responsible for a variety of functions in the body, including maintaining the function of the immune system, aiding vision and ensuring skin and tissue lining health. Vitamin A is found in the retinol form most often in dairy products and liver, while brightly colored fruits and vegetables primarily contain provitamin A carotenoid. Osteoporosis strikes the most people in the northern parts of Europe, a part of the world that consumes the retinol form of vitamin A in high amounts. Researchers theorize that consuming high amounts of vitamin A may inhibit the ability of vitamin D to stimulate the absorption of calcium, resulting in gradual bone weakening.

Research

Studies focusing on the connection between vitamin A intake and osteoporosis indicate that both men and women who consume large amounts of vitamin A, either from their diet or supplementation, have a greater risk of experiencing fractures due to weakened bones only when it is retinol -- the animal product-based form of vitamin A -- that is consumed in excess. The research indicates that the risk was not dependent on the source of the vitamin A and that, in most cases, intake needed to be at least twice the recommended daily levels. The Office of Dietary Supplements advises that there is no evidence to indicate that the plant-based form of vitamin A contributes to osteoporosis risk.

Expert Insight

The Institute of Medicine recommends that children between the ages of 1 and 13 should consume between 300 and 600 mcg of retinol daily, while adult men and women should consume between 700 and 900 mcg per day. Speak to your doctor about your risk of osteoporosis if you regularly consume foods rich in the retinol form of vitamin A; do not begin taking vitamin A supplements unless you are under the direction and supervision of your doctor. At this time, there is no recommended daily intake for vitamin A in the form of provitamin A carotenoids.