Oxidized LDL could be lethal in another manneras well: by attracting "foam cells" ormacrophages, which cause plaque to grow on arterywalls, the molecule may lead directly to heartdisease.

Through its ability to scavenge free oxygenions, beta carotene could undermine the dangerousoperation of the LDL molecules and thus reducecancer and heart disease risk.

For decades, chemists have known of themolecule's uncanny ability to grab onto chargedoxygen ions nearby. But only in the past decade orso have clinicians found a medical use for suchinformation.

One of the earliest to do so was Mathews-Roth,who legitimized beta carotene as a viable medicaldrug in the mid-1970s. Then working onprotoporphyria, an obscure disease which rendersits sufferers highly sensitive to light,Mathews-Roth stumbled across the organic moleculeas a treatment.

Protoporphyria victims suffer from a defectiveenzyme, which causes the protoporphyrin moleculeto seep into the subject's skin rather thanincoporating itself into the oxygen-carryinghemoglobin in the bloodstream, where it belongs.At the body's surface, the errant molecule reactswith oxygen in the air, causing severe itching andburning.

Mathews-Roth found that huge doses of betacarotene--up to 180 milligrams a day--can preventthe protoporphyria molecule from reacting withoxygen, and thus cures protoporphyria in all butthe most severe cases.

"The vast majority of people will be able to goout in the sun," says Mathews-Roth, whosetreatment won approval in 1975 from the Food andDrug Administration for her discovery.

Both Hennekens and Mathews-Roth admit that herprotoporphyria research was an important step inthe evolution of the Physicians' Health Study. Bydemonstrating that huge doses of beta carotene hadno adverse effects on the subjects (except for therather unfortunate consequence of turning theirskin yellowish-orange), she was able to sellHennekens on the safety of the drug in alarge-scale clinical trial.

"It had an important impact on our thinking,"recalls Hennekens. "The [subjects] didn't have anybiological abnormalities."

Contradicting Evidence

Researchers are quick to point out that theirtheories are still speculative, and conclusiveproof is still at least half a decade away. Butalready, the much-heralded panacea has taken abeating from some investigators.

In one study published earlier this year,researchers at the Anderson Cancer Center inHouston found that beta carotene did not performas effectively as current treatments in reversingoral cancer.

Scott M. Lippman of the University of Texasgave the drug to one group of oral leukoplakiasufferers for a duration of three months, whileadministering to another group the proventreatment 13cRA. At the end of the study, none ofthe 13cRA group and half of the betacarotene group progressed to cancer. The resultswere published in The Journal of the NationalCancer Institute.

Within a few days of that announcement,Dartmouth researchers presented a study whichshows beta carotene was ineffective in treatingskin cancer after three to five years. E. RobertGreenberg of the Norris Cotton Cancer Centerauthored the study, which he published in TheNew England Journal of Medicine.

The skin is "a site that doesn't seem to beclosely related to dietary intake," Greenberg saidin a phone interview.