Drug Profile

Acute vitamin A toxicity in humans is rare but is more likely to occur following ingestion of high-dose supplements, rather than following high intakes of vitamin A from food. Vitamin A accumulates in the body; therefore, individuals who have regular high daily intakes of vitamin A might suffer adverse effects from chronic hypervitaminosis A. Although most manifestations of chronic vitamin A toxicity are reversible on cessation of dose, permanent damage to liver, bone, and vision and chronic muscular and skeletal pain may occur in some cases.

It is not possible to establish a safe upper level for vitamin A. There are two threads of evidence regarding potential adverse effects of vitamin A, one on teratogenicity and one on the risk of bone fracture, which suggest different levels of intake at which adverse effects may occur. Both of these ranges appear to overlap with dietary intakes of vitamin A.

A number of epidemiological studies have suggested that high doses of vitamin A may be teratogenic, that is, that they could cause malformations in the unborn child. The Expert Group on Vitamins and Minerals note and endorse the current advice that women who are pregnant or who wish to become pregnant should not take dietary supplements containing vitamin A except on medical advice.

In studies of long-term dietary intake, vitamin A has been associated with decreased bone density and increased risk of hip fracture. Research published in the Jan. 2, 2002 Journal of the American Medical Association suggested that a high intake of vitamin A from supplements and food is associated with an increased risk of hip fracture in postmenopausal women.[1]

The risk of hip fracture is a continuous graded response associated with exposure levels that include average dietary intakes. It is not possible to identify an intake that is without some degree of risk. However, the available data indicate that total intakes greater than 1,500 micrograms (5,000 IU) per day may be inappropriate. (Note that this is only approximately twice as high as the recommended daily allowance for older adults—see Vitamins and Minerals.)

A recent extensive review of this topic concluded that “Until further information is available, patients should be made aware of the potential risks of consuming vitamin A in amounts that exceed the recommended dietary allowance. Further research is needed to clarify the relationship between vitamin A and fracture risk.”[2] (emphasis supplied)

Data on retinol intakes from food and supplements suggest that high-level consumers of liver and liver products and/or supplements may exceed intakes at which adverse effects have been reported in the literature. It should also be noted that dietary supplements may contain 20–100% more vitamin A than is stated on the label, due to the practice of using “overages” within the food supplements industry to ensure that the product contains no less than the stated content of the vitamin throughout its shelf life. This may be particularly important given that the effect on fracture risk appears to be a graded response, with the risk of fracture increasing with increased intake.”[3]

Vitamin A is necessary for growth and bone development, vision, and healthy skin. It is found in many foods (see boxes above), and a well-balanced diet with a variety of healthful foods should supply all the vitamin A that your body needs. The recommended dietary allowance (RDA) of vitamin A is 900 micrograms per day for men and 700 micrograms per day for women, corresponding to 2,970 and 2,310 international units (IU) respectively. These amounts are easily achieved through a good diet.

Vitamin A deficiency is rare, but older adults may develop this deficiency if they have certain intestinal or liver diseases, an overactive thyroid (hyperthyroidism), or diabetes. You may also develop vitamin A deficiency from an inadequate diet or if you take certain drugs such as cholestyramine, colestipol, mineral oil, neomycin, or sucralfate. The liver stores enough vitamin A to last several months, so symptoms of a deficiency may take a few months to develop. The symptoms include night blindness and dry, cracked skin.

If you have to increase your intake of vitamin A to prevent or treat a deficiency, eat more foods that are rich in the vitamin rather than taking a vitamin supplement. You can get vitamin A from foods in two main forms. Animal sources such as liver, egg yolks, and butter provide a form of vitamin A called retinol. Plant sources such as carrots, squash, and some fruits provide a substance called beta-carotene, which your body converts into vitamin A in the body. Plant sources have several advantages over animal sources, the main one being that they are low in calories, fat, and cholesterol and high in fiber and other nutrients.

Some researchers claim that people who eat large amounts of foods containing beta-carotene have a lower risk of some types of cancer than those who eat less of these foods.[4] However, one large 12-year study found that beta-carotene supplements had no effect on the incidence of cardiovascular disease or malignancy. A second controlled clinical trial in Finnish smokers found an increased incidence of lung cancer of 18%, which was statistically significant.[5] No one should take beta-carotene supplements.

A recent Journal of Parenteral and Enteral Nutrition (JPEN) systematic review revealed that, with a few possible exceptions, dietary supplements offer no benefits to well-nourished adults eating a Western diet and, in many cases, may be harmful. The results of this study reinforce Worst Pills, Best Pills News’ longstanding view that there is little evidence that dietary supplements are either safe or effective.

The study authors concluded that with the possible exception of vitamin D in elderly patients and omega-3 fatty acids in patients with a history of cardiovascular disease, no data support the widespread use of dietary supplements in the U.S. and other Western countries. Indeed, the data suggest that certain commonly used dietary supplements, including beta-carotene, vitamin A and vitamin E, may be harmful. We agree.[6]

If you use vitamin A supplements despite our recommendation not to and without a doctor’s supervision, do not exceed the RDA. Taking doses only slightly higher than the RDA can be risky. Unlike with some other vitamins, your body cannot eliminate excess vitamin A, so the vitamin can accumulate to dangerous, toxic levels in your body. The toxic effects of too much retinol include liver damage, weakness, increased pressure in the brain, bone and joint pain and damage, and dry, rough skin. The effects from beta-carotene are not as serious, but we nevertheless do not recommend using beta-carotene supplements either.