Food sources of vitamin A
Excess vitamin A and fracture risk
Vitamin A can come in the natural form or as the provitamin, beta carotene, which is widely distributed in plants. Note that beta carotene was not found to be a predictor of low BMD in these studies–just serum retinol. See the 1UpHealthsite for excellent tables showing animal sources and plant sources of vitamin A. As you look at these tables, recall that the Rancho Bernardo Study found an inverse U-shaped association between vitamin A intake and bone mineral density (BMD). BMD was optimal when the vitamin A intake was 2000 to 2800 IU per day (0.6 to 0.9 mg per day). Thus, both low and high intakes of vitamin A are deleterious to bone health. You’ll note that many natural food sources have many times more than the ideal daily intake of vitamin A in them. And, don’t forget supplemented food sources. I heard from a man with osteoporosis interested in this topic who found that his daily vitamin pill had 5000 IU of vitamin A. Imagine that he takes that with his bowl of Total cereal which also has 5000 IU of vitamin A, has a few carrots, some milk fortified with vitamin A (10% of daily need), and a few other sources. It isn’t hard to see how someone who isn’t careful about the food eaten or the supplements taken could get into bone density trouble pretty easily. Also, see Consumerlab.com for the names and amounts of vitamins and minerals in several multivitamin supplements. Most have 5000 IU, with the lowest having 1667 and the highest having 10000 IU.
In the NEJM study by Michaelsson and others, men in the 99th percentile of serum retinol (vitamin A) had seven times the risk of fracture of men in the lowest levels of serum retinol. Thus, the risk of fracture can be very significant with very excessive doses of vitamin A. Note that current recommended intake of vitamin A is 0.7 mg/day for women and 0.9 mg/day for men which correlates quite well with the Rancho Bernado Study findings. In terms of serum levels of retinol, the authors found that values greater than 86 microg per deciliter may increase the risk of fracture. The ideal range appears to be from 20.1 to 80.2 microg per deciliter. It is significant that in the study on rats, those taking the equivalent of 9000 IU/day had thinning of the bone cortex and reduced three-point bending breaking force indicating weakened bones. A person taking one multivitamin and eating Total cereal daily would be over the amount of vitamin A the rats ingested. The rats had no clinical signs of toxicity at the levels of vitamin A ingested, so bone harm can happen without any other signs or symptoms of excessive vitamin A. Another important finding–contrary to what happens with vitamin D, for instance–is that serum retinol increases with age, thus putting older people at greater risk of hypervitaminosis A.
What can be done about this problem?
I don’t have the answer for sure. Some thoughts that occur to me would be to contact your representatives in Washington, D. C. and see what government oversight is being done to see that foods are not overly fortified with potentially dangerous vitamins. You could write to the makers of these supplements and ask for them to lower the vitamin A dosage or put a warning on the label. It might be possible to contact the FDA with the same request, too. I’m open to suggestions if anyone has a better idea.