Vitamin A: Bone Poison?
Too Much Vitamin A Can Weaken Your Bones
Jan. 22, 2003 -- Getting too much of a good thing may be partially responsible for the rise of osteoporosis and brittle bones among older people in the U.S. and other developed countries. A new study shows excessive intake of vitamin A can increase a person's risk of bone fracture by as much as seven times, and current fortification levels may need to be reassessed.
Prior studies have suggested that vitamin A plays a role in the gradual weakening of bones frequently associated with age, but this study is the first to show a link between levels of vitamin A in the blood and the long-term risk of bone and hip fracture.
Researchers say the findings suggest that excessive vitamin A intake may explain, in part, the high rates of hip fractures in Scandinavia and the United States where the use of vitamin supplements and vitamin A fortification is common.
Fortification of dairy products and cereals with vitamin A began in Scandinavia and the U.S. several decades ago in an effort to prevent night blindness, which is often the first sign of vitamin A deficiency. Vitamin A deficiency is also a major cause of blindness in developing countries.
In the study, Swedish researchers measured vitamin A (retinol) levels in blood samples from 2,300 men who were followed for up to 30 years and then compared those levels with fracture rates among the group.
They found men who had the highest levels of vitamin A at the start of the study were significantly more likely to suffer a bone or hip fracture, and the overall risk of fracture increased 64% in men with the highest levels compared with those with average levels. The risk of fracture among those with the highest levels of vitamin A was seven times higher than those with the lowest levels.
The findings are published in the Jan. 23 issue of The New England Journal of Medicine.
Laura Tosi, MD, chair of the women's health issues committee for the American Academy of Orthopaedic Surgeons, says the findings could have a huge impact on efforts to prevent osteoporosis. She says statistics show that an older person who breaks a bone is very likely to break another one and is at high risk of losing their independence due to a hip or vertebrae (back) fracture.
"What these results indicate is, 'Oh my God we have found a bone poison,'" says Tosi, who is also associate professor of orthopaedic surgery and pediatrics at the George Washington University School of Medicine. "Vitamin A is important in small doses, but at high doses it is bone poison."
Concentrations of vitamin A vary in different supplements, but researchers found that consuming more than 1.5 mg per day of vitamin A from supplements increased the risk of fracture.