Vitamin A and Birth Defects
By
VRP Staff
The release of data from a Boston University research report, published in the November 23rd issue of The New England Journal of Medicine, focused
national attention on the risk of birth defects when a pregnant woman takes relatively high doses of vitamin A. This risk has been well known since at least the mid-70s. While the present study has not yet been released, its apparent value will be to confirm a safe upper limit of 10,000 IU/day from preformed (animal origin) vitamin A. Prudence would argue for an even lower intake, as explained below.
The press release did the public a disservice by not differentiating between preformed vitamin A and carotenoids (from dietary plant sources or supplemental carotene.) The study in question clearly relates only to preformed vitamin A. Only the preformed vitamin A has the potential for toxicity. Carotenoids, such as the popular supplement beta-carotene, have never been linked to vitamin A toxicity. However, since carotenoids are also measured in vitamin A activity, consumers may be confused by seeing a label totaling vitamin A activity from both sources, such as:
Vitamin A 25,000 IU from retinyl palmitate 2,500 IU from beta-carotene 22,500 IU
Only the retinyl palmitate is potentially toxic in larger doses.
On a more general level, it is worth repeating that fat-soluble vitamins (Vitamins A, D, E, and K) do accumulate in body tissues and organs and, as such, upper limits of safe consumption do exist. In the case of vitamin A, multivitamin capsules routinely providing over 10,000 IUs/day of preformed vitamin A should have disappeared from the market long ago. High requirements of vitamin A activity should be met principally from beta-carotene, with only 2,500 to 5,000 IUs of preformed vitamin A. It would be unwise to depend 100% on provitamin A (beta-carotene) in a dietary supplement, as hypercarotenemia can occur in persons with an inherited inability to convert carotene to retinol, as well as a result of certain illnesses such as diabetes mellitus and hypothyroidism.
In considering targets for preformed vitamin A dietary intake and supplementation, it is useful to note that the FDAs U.S. RDA of 5,000 IU is their average value for the populace. While this value is based on recommendations of the National Research Council (RDAs) for preformed vitamin A, it also assumes a certain dietary intake of carotenoids. Thus it could be met from a diet of 2,500 IU of preformed vitamin A (the NRCs RDA for males over 10 years and pregnant women) and 2,500 IU from carotenoids. By certain authorities, the U.S. RDA of 5,000 IU should be considered to be 3,300 IU when supplied by preformed vitamin A alone.
Excluding the case of birth defects, chronically high doses of preformed vitamin A appear to start producing hypervitaminosis A symptoms in adults above the level of 100,000 IUs per day, with childrens limits lower and somewhat proportional to body weight. Acute hypervitaminosis A results most often from short-term overuse of supplements, usually due to misuse by the consumer, or overprescribing by a physician. The classic cases of overdose due to consumption of livers of carnivorous animals or larger fish, probably important to our prehistoric ancestors, are rare today.
Despite vitamin As reputation for potential toxicity, vitamin A deficiency is far more common than cases of toxicity, with an estimated 200 cases of hypervitaminosis A annually versus one million persons developing vitamin A deficiency each year. In underdeveloped countries the deficiency is the second most common effect leading to progressive blindness. In the US, the NHANES II study showed 20% or more of the population was receiving less than 70% of the RDA. A shortage is particularly critical during pregnancy when a deficiency can result in birth defects.
Danger to the fetus from high doses of preformed vitamin A ( as well as from a vitamin A deficiency) is a risk in the first few weeks of pregnancy. For this reason, intake must be adequate, and not excessive in the month prior to pregnancy. The most commonly reported source of excess vitamin A-caused birth defects is the dermatological use of vitamin A analogues such as Accutane, Roaccutane, and Tigasan. These, then, must be used under a physicians supervision and discontinued a month or more prior to any pregnancy.