Vitamin A and Bone Loss.

Date:

28-Jan-2003

Source

New England Journal of Medicine

Related Monographs

Consumer Data: Vitamin A
Professional Data: Vitamin A

Article

Vitamin A wasn't even known about until 1913, when scientists discovered it could prevent night blindness. Then, in 1932 it was discovered that beta-carotene, also known as pro-vitamin A, was the precursor to vitamin A. When we consume beta-carotene, vitamin A is produced naturally by enzymes in the digestive tract that break beta-carotene down. The fat-soluble vitamin A is then stored in the liver, where it can remain for long periods of time. Vitamin A occurs only in animal products like liver, kidney, butter, egg yolks, whole milk and fortified skim milk. Meanwhile, beta-carotene is found in yellow fruits and vegetables like carrots, sweet potatoes, squash, apricots and cantaloupe, and in dark leafy vegetables like collards and spinach.

Of concern are some findings regarding vitamin A in The Nurses' Health Study. The Nurses' Health Study has evaluated the health over 72,000 postmenopausal women 34 to 77 years old for a variety of reasons. One group of investigators evaluated the relationship between high vitamin A intake from foods and supplements and the risk of hip fracture among 72,337 postmenopausal women. Women in the highest group of vitamin A intake had higher risk of a hip fracture than the women in the group with the lowest intake of vitamin A. Women using estrogen decreased this risk and the use of beta-carotene did not significantly increase the fracture risk.1

A recent study published in the New England Journal of Medicine investigated this potential hazard in 3,322 men between the ages of 49 and 51. Serum levels of vitamin A and beta carotene were measured and these individuals were followed for 30 years. 266 men experienced bone fractures over this time period. During these 30 years, researchers found that the risk of bone fractures was higher among the men with higher serum levels of vitamin A. The levels of beta carotene were not associated with fractures. The authors of this study concluded that the amounts of supplementation of vitamin A need to be reassessed in many Western countries.2

References

1. Feskanich D, Singh V, Willett WC, Colditz GA. Vitamin A intake and hip fractures among postmenopausal women. JAMA. Jan2002;287(1):47-54.
2. Michaƫlsson K, et al. Serum Retinol Levels and the Risk of Fracture. New Eng J Med. Jan 2003;348(4):287-294.