In my recent post "Why taking cod liver oil is not a good idea" (1) I made the point that vitamin D supplementation is vital in the winter months, but that getting the sunshine vitamin from cod liver oil is not a good idea. Cod liver oil contains high amounts of vitamin A as preformed retinol. Taking it in amounts necessary to reach effective vitamin D levels can therefore lead to vitamin A toxicity (hypervitaminosis A). In addition, high levels of vitamin A actually negate the effect of vitamin D, the very reason for taking cod liver oil in the first place.

A reader pointed out that this advice is at odds with Adelle Davis′ vitamin A recommendations. In her book "Let′s get well", she apparently claimed that vitamin A deficiency is more widespread than is generally admitted, and that amounts of up to 50,000 IU/day are quite safe and often useful for fighting infections.

I have to admit that I had never heard of Adelle Davis; I had never come across any of her books. According to Wikipedia (2), Adelle Davis (1904 - 1974) was a pioneer in the American health movement, a trained dietitian with a degree in biochemistry. She published a number of books on health and nutrition, the last of which, "Let′s get well", came out in 1965. Nobel laureate and vitamin C guru Linus Pauling acknowledged that "… she was essentially correct in almost everything she said" (2). High praise indeed.

I didn′t find her book at the local library and I therefore don′t know where she got her numbers from. They are much higher, though, than today′s recommendations.

How widespread is vitamin A deficiency?

Vitamin A deficiency is endemic in developing countries and causes a variety of health problems (3). A lack of vitamin A is the leading cause of blindness in the Third World. In those countries carotenoids from plant foods are the principal sources of vitamin A, and carotenoids are less well absorbed than preformed retinol. Malnutrition often compounds the problem.

In industrialized countries, on the other hand, people generally take in enough preformed retinol from fortified foods and multivitamins to reach effective vitamin A levels (3). In fact, observational studies suggest that 75% or more of Americans may routinely ingest more than the recommended dietary allowance for vitamin A, much of it as preformed vitamin A (4). Getting vitamin D from retinol-rich cod liver oil can therefore easily lead to vitamin A overload.

What are the current vitamin A recommendations?

The Food & Nutrition Board of the U.S. Institute of Medicine currently recommends 900 μg (3,000 IU) per day for men and 700 μg (~2,300 IU) for women, with lower values for infants and children, and somewhat higher amounts for nursing women (5). 0.3 μg of vitamin A equals 1 IU (6).

Are these values too low? The Independent Vitamin Safety Review Panel, an independent panel of physicians, academics and researchers, doesn′t think so. In their October 2007 call for a reassessment of vitamin and mineral recommendations they specifically exempt vitamin A:

“Government-sponsored nutrient recommendations, such as the US RDA/DRIs, are not keeping pace with recent progress in nutrition research. While current official recommendations for vitamin A, iron, calcium, and some other nutrients are generally adequate, the public has been asked to consume far too little of many other key nutrients. Inadequate intake, and inadequate standards to judge intake, have resulted in widespread nutrient inadequacy, chronic disease, and an undernourished but overweight population.” [emphasis added] (7)

What evidence is there for vitamin A toxicity?

The main concern with excess vitamin A intake is its possible adverse effect on bone mineral density (BMD), which in turn can lead to an increased risk of hip fractures (3,4). There is sound biochemical evidence for the involvement of vitamin A in bone metabolism. Vitamin A is known to interfere with vitamin D and with calcium-regulating hormones (3,4).

Clinical observations, on the other hand, have shown mixed results (3,4). Some investigators found bone toxicity effects at vitamin A levels as low as twice the daily dietary allowance, whereas others found no correlation between vitamin A intake and hip fractures (3,4). There is enough evidence though for a link between high vitamin A levels and an increased risk of fractures to advise caution (3,4). The Linus Pauling Institute, which certainly supports vitamin/mineral supplementation, also warns against taking excessive amounts of retinol:

"The RDA for vitamin A (2,300 IU/day for women and 3,000 IU/day for men) is sufficient to support normal gene expression, immune function, and vision. However, following the Linus Pauling Institute’s recommendation to take a multivitamin/multimineral supplement daily could supply as much as 5,000 IU/day of vitamin A as retinol, the amount that has been associated with adverse effects on bone health in older adults. For this reason, we recommend taking a multivitamin/multimineral supplement that provides no more than 2,500 IU of vitamin A or a supplement that provides 5,000 IU of vitamin A, of which at least 50% comes from beta-carotene. High potency vitamin A supplements should not be used without medical supervision due to the risk of toxicity". [emphasis added] (6)

All in all, the advice to avoid cod liver oil because of its high vitamin A content seems sound. I could find no support among today′s experts for Adelle Davis′ high vitamin A levels.

Sources:

1. Helmut Beierbeck. Why taking cod liver oil is not a good idea.
   http://healthcomments.info/2009/01/27/why-cod-liver-oil-is-not-a-good-source-of-vitamin-d.aspx
2. Adelle Davis. Wikipedia.
   http://en.wikipedia.org/wiki/Adelle_Davis
3. Cannell JJ et al. Cod liver oil, vitamin A toxicity, frequent respiratory infections, and the vitamin D deficiency epidemic. Ann Otol Rhinol Laryngol 2008;117(11):864-870.
4. Penniston KL, Tanumihardjo SA. The acute and chronic effects of vitamin A. Am J Clin Nutr 2006;83:191-201.
   http://www.ajcn.org/cgi/reprint/83/2/191
5. Dietary Reference Intakes: Vitamins. http://www.iom.edu/Object.File/Master/7/296/webtablevitamins.pdf
6. Vitamin A. Micronutrient Information Center. Linus Pauling Institute.
   http://lpi.oregonstate.edu/infocenter/vitamins/vitaminA/
7. Doctors say, raise the RDAs now. Orthomolecular Medicine News Service, October 30, 2007.
   http://orthomolecular.org/resources/omns/v03n10.shtml