Q. I was astounded by your last column that multivitamins and antioxidants may actually cause cancer. I've been taking these more than 10 years to prevent cancer. Why is this not front-page headlines?

A. There's been such heavy marketing of vitamins and antioxidants that the public and even many physicians believe in their benefits as gospel truth. There's the belief that they're natural, so they can't possibly harm and can only benefit. Studies showing harm are therefore ignored.

Remember how we all thought that estrogens reduced heart disease? Estrogen improves cholesterol, and in 1985, a study of 32,000 women found that estrogen users had 50 percent less heart disease. But later studies showed the opposite. Why should we believe these? Because these are much more accurate studies known as randomized controlled trials. The 1985 study was an observational study that followed two groups of women — those who decided to take estrogen and those who didn't. But the women who took estrogen were different from those who chose not to: They exercised more and ate better.

These so-called confounding factors were the real reasons these women had fewer heart attacks. With observational studies, you can never be sure you've corrected for all the confounders. In randomized controlled trials, folks are randomly assigned to two groups: one takes the drug or vitamin and the other takes a fake pill. Only the trials can eliminate confounders and show the true effects of our potions. This is something even many physicians and "experts" from big name universities don't realize.

In 2002, Dr. David Waters and others did a randomized controlled trial on 423 women with heart disease, putting half of them on 800 IU of vitamin E plus 1,000 mg of vitamin C a day. After four years, 16 of those on vitamins had died, compared with six not on vitamins. For vitamin E, other randomized controlled trials show harm above 150 IU a day, so Kaiser no longer sells doses above 100 IU.

On Feb. 28, Dr. Goran Bjelakovic and others looked for all randomized controlled trials ever done on this topic. Combining the results of 47 such trials involving 180,000 subjects, both healthy and sick, he found that beta-carotene, vitamin A, or vitamin E, taken singly or combined with other antioxidants, indeed increases your chance of dying from heart disease, cancers and other causes.

Taking antioxidants reduces free radicals, but free radicals help your body destroy unwanted cells like germs, precancers and cancers.

In an effort to boost immunity, Dr. Craig Albright and others in the Journal of Nutrition in 2004 fed mice a diet with no vitamin E or vitamin A. These mice had less breast cancer with less metastasis to their lungs, and their tumors had more free radicals and more cell death compared with mice taking these vitamins.

Dr. 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; fax 535-8170; or write islandlife@honoluluadvertiser.com. This column is not intended to provide medical advice.