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2009-03-18 07:33:21
Vitamin A is a fat-soluble vitamin required for vision, growth, reproduction,
cell growth and differentiation, and a healthy immune system. It's a common
ingredient in multivitamins. Recent studies, however, suggest that excessive
vitamin A intake is associated with an increased risk of fracture.
A study published in the New England Journal of Medicine followed 2322 men in
Sweden for 30 years. Researchers found that the fracture risk was greatest in
men with the highest blood levels of retinol, one of the most active forms of
vitamin A.
Another study found similar results. The Nurses Health Study looked at 72,337
postmenopausal women over an 18 year period and found that women who consumed
at least 3000 mcg a day as retinol equivalents were 48% more likely to have a
hip fracture compared to women whose daily intake was less than 1250 mcg (4125
IU) per day.
Retinol may interfere with the activity of vitamin D, a vitamin that
facilitates the absorption of calcium.
The Centers for Disease Control and Prevention (CDC), however, reviewed data
from the 5,800 people in the third National Health and Nutrition Examination
Survey (1988-94) to determine whether there was an association between bone
mineral density and blood levels of vitamin A (in the form of retinyl esters).
They didn't find an association.
Retinol is the form of vitamin A found in most multivitamins and in cod liver
oil, liver, fortified foods, and whole milk products. Beta carotene, which is
converted to vitamin A in the body (and another common multivitamin
ingredient), was not associated with an increased risk of fracture. Beta
carotene is found in carrots, tomatoes, cantaloupe, spinach and other fruits
and vegetables.
The recommended dietary allowance (RDA) of vitamin A for men over 18 is 900 mcg
(3000 IU) and for women it's 700 mcg (2,310 IU). This calculation should
include all sources of retinol, including foods such as liver, dietary
supplements such as multivitamins, cod liver oil, and vitamin A supplements,
and fortified foods such as cereal. The upper limit for retinol is 3000 mcg
(10000) IU per day.
Until we know more, it would be wise to check your supplements (especially your
multivitamin), and consult your healthcare provider before taking vitamin A
supplements to avoid possible adverse effects.
Sources
Ballew C, Galuska D, Gillespie C. High serum retinyl esters are not associated
with reduced bone mineral density in the third National Health and Nutrition
Examination Survey, 1988-94. J Bone Miner Res 2001;16:2306-12.
Feskanich D, Singh V, Willett WC, Colditz GA.Vitamin A intake and hip fractures
among postmenopausal women.JAMA 2002 Jan 2;287(1):47-54.
Michaelsson K, Lithell H, Vessby B, Melhus H. Serum retinol levels and the risk
of fracture. New England Journal of Medicine. 2003;348:387-94.
Johansson S, Lind PM, HAKansson H, Oxlund H, rberg J, Melhus H. Subclinical
hypervitaminosis A causes fragile bones in rats. Bone. 2002;31:685-9.
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Posted: 2009209@447.51
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POINTS
- A study published in the New England Journal of Medicine followed 2322 men in
Sweden for 30 years. Researchers found that the fracture risk was greatest in
men with the highest blood levels of retinol, one of the most active forms of
vitamin A.
- Retinol may interfere with the activity of vitamin D, a vitamin that
facilitates the absorption of calcium.
- Retinol is the form of vitamin A found in most multivitamins and in cod liver
oil, liver, fortified foods, and whole milk products. Beta carotene, which is
converted to vitamin A in the body (and another common multivitamin
ingredient), was not associated with an increased risk of fracture. Beta
carotene is found in carrots, tomatoes, cantaloupe, spinach and other fruits
and vegetables.