Q. Astaxanthin is a caroten-oid antioxidant found in marine animals and vegetables. Can I take it to protect my skin from the sun's ultraviolet rays?

A. I searched the published literature and found two studies showing that astaxanthin reduced markers of DNA damage from ultraviolet A light in cultured cells. Another two found it reduced UVA oxidative stress in both rat kidney cells and the skin of hairless mice.

But in a December 2006 study, Marcello Santocono and others found that in some cells, astaxanthin actually worsens DNA damage. And in 1998, Homer Black reported in Nutrition & Cancer that astaxanthin actually increased skin cancers in hairless mice.

Astaxanthin has 500 times the antioxidant activity of vitamin E and 10 times that of beta-carotene, but this may do more harm than good. In 2002, David Waters and others studied 423 women with heart disease, putting half on 800 International Units of vitamin E plus 1,000 mg of vitamin C a day. After four years, 16 vitamin users had died compared with six not on vitamins.

In the June 2003 issue of Lancet, a Cleveland clinic meta-analysis found that beta-carotene increased deaths from heart disease. And the New England Journal of Medicine found that smokers taking beta-carotene and vitamin A had more lung cancer deaths. But when folks die from cancers or heart disease, doctors blame other things on the death certificate besides vitamins, so you won't see these excess deaths from vitamins reflected in government statistics.

So what's happening? There are about 600 known carotenoids. Fruits and vegetables have hundreds of beneficial molecules. It could be that a combination of most of these taken in the correct proportion is reason for reduced cancers and heart disease. But if you take extra beta-carotene, vitamin E, and perhaps astaxanthin, it's no longer natural and may throw off the balance of the substances you ingest in the normal, correct proportions from foods, causing disease or premature aging by artificially altering dozens of biochemical reactions occurring simultaneously in your body.

Taking several vitamins in combination may not work, and may only add their individual toxicities. Perhaps the unique way astaxanthin orients itself in cell membranes will make it different from beta-carotene and reduce heart disease, but this remains to be seen.

Due to recent systematic reviews of multiple studies showing harm, Kaiser last year decided to stop selling vitamin E above 100 IU, and this year stopped selling beta-carotene and vitamin A entirely.

In summary, no published study has shown an actual reduction in skin cancers or sun damage. You're at risk for skin cancers or premature aging if you use an unproven product for photoprotection.

Landis Lum is a family-practice physician for Kaiser Permanente and an associate clinical professor at the University of Hawai'i's John A. Burns School of Medicine. Send your questions to: Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; islandlife@honoluluadvertiser.com; or fax 535-8170. This column is not intended to provide medical advice.