Herbs, supplements and HIV

January 2005     View PDF     En español

Vitamin A (beta-carotene and retinoids) and
anti-HIV drug interactions

In general, when used at reasonable doses on their own, nutritional products like vitamin A supplements are considered safe. New information suggests that when used with other therapies, including anti-HIV drugs and other nutritional products, interactions may occur that alter a product’s effectiveness and safety.

Deficiencies in vitamin A (retinol, beta-carotene) have been associated with advanced HIV disease. It remains unclear if taking vitamin A supplements such as retinoids or beta-carotene helps people with HIV beyond correcting the deficiency. Moreover, questions remain as to whether or not vitamin A supplements cause vitamin-drug interactions.

A team in Canada set out to evaluate whether or not different vitamin A supplements interact with the p450 enzyme. The team evaluated four tablets and two soft gel capsules. All of the tested products had lower beta-carotene content than stated on their labels. One product had ten-fold less beta-carotene than advertised, and most were at least half as much than stated.

All forms of vitamin A (retinal, retinol, retinate and beta-carotene) as well as all the products tested had moderate (45–65%) to strong (65–100%) inhibitory effect on the p450 enzyme. Therefore, these products (and possible other nutritional health products) are very likely to interact with anti-HIV drugs. However, human studies are needed to understand the extent of these findings.

These data suggest that there are possible, real vitamin-drug interactions with potentially harmful results for people taking anti-HIV drugs. Much more information is needed to fully understand the scope of these interactions and their impact on the effectiveness and side effects of therapies. This information would also be needed on how to modify doses of either therapy to reduce the risk of developing drug resistance and increase the chances of benefiting from both.