Everyone wants to stay young, so the anti-aging market is huge. Walk into any vitamin shop or health-food store, and you'll see that one of the hottest sellers is supplements containing DHEA. But before you buy, here's what you need to know about anti-aging pills -- including Good Housekeeping's surprising discovery.

What is DHEA? It's a hormone (dehydroepiandrosterone) that your body converts to testosterone and estrogen. DHEA levels start declining for people when they're in their 30s (sometimes sooner), and many scientists associate that drop with increased body fat, decreased bone mass, higher cholesterol, memory loss and reduced libido. The theory is that lifting your DHEA level with supplements will reverse or slow the signs of aging.

The controversy: Proponents claim there are studies that prove DHEA's anti-aging effects. That's nonsense, say critics, who caution that more research is needed. "Many tests they cite were done on rodents, and the results don't necessarily translate to DHEA's effectiveness in people," said Marc Blackman, M.D., an endocrinologist at the National Institutes of Health. What's more, he said, the long-term side effects are unknown (short-term effects may include acne and insomnia). Many doctors speculate that long-term DHEA use might lead to liver damage and breast and prostate cancers. One doctor's bottom line: "Consumers shouldn't muck with their hormones," said Stephen Barrett, M.D., of Quackwatch, a nonprofit that fights health fraud.

Are you getting the real thing? Because these pills are classified as dietary supplements rather than as drugs, companies distributing DHEA products are not required to prove their safety or effectiveness to the Food and Drug Administration. Pamela Wartian Smith, M.D., an anti-aging specialist in Michigan, points out that over-the-counter DHEA has the same problem that many other dietary supplements do: It might not be 100 percent pure. Smith supports DHEA use but believes the hormone should be regulated by the FDA. She prescribes pharmaceutical-grade pills that are individually compounded by a pharmacist; an outside company verifies their purity and dose.

Dose does matter: "Women are very sensitive to DHEA," said Smith, who rarely prescribes more than 15 milligrams. Too much can cause side effects; too little won't produce real results. Roxanne England, R.D., a specialist for the quality-control and compliance team at Swanson Health Products, a maker of dietary supplements, told Good Housekeeping that her firm began manufacturing 50-mg pills because customers wanted a higher dose, and studies showed that an increase would be safe. But the supporting study she cited was one conducted with HIV patients who took 500 mg of DHEA. Even she admitted it was "a bad example."

Good Housekeeping discovered a study that was conducted in the year 2000 that found no harmful side effects in healthy people who took 50 mg daily for a year. But for many doctors, the jury is still out -- especially on the long-term effects.

Good Housekeeping's shocking discovery: Four of the eight brands of DHEA that Good Housekeeping sent to an independent lab failed to accurately state the level of DHEA in their product. The pills contained less DHEA than the labels claimed. Good Housekeeping's take: These companies are misleading customers.

Recalls Alert

The following products and vehicles were recalled by the Consumer Product Safety Commission and the National Highway Traffic Safety Administration. Unless otherwise indicated, discontinue use of the products immediately and return them to the store where purchased for a refund. For more information about the products, call the manufacturer or CPSC's toll-free hotline, (800) 638-2772. Only some cars or trucks recalled are affected. Contact a dealer for your model to see if it is included in the recall. The dealer will tell you what to do.

J.C. Penney Crazy Daisy 3-in-1 Electronic Motion Shade Lamps, sold at J.C. Penney stores, through its catalog and Web site from June 2005 through March 2006 for about $30. The electrical circuit board can spark and overheat because of an electrical problem, posing a fire hazard. Return it to any J.C. Penney store for a refund or call J.C. Penney at (888) 333-6063.

2004 Chevrolet Avalanche; 2004-05 Chevrolet Suburban; 2004-06 Chevrolet Silverado, GMC Sierra, GMC Yukon XL; 2005-06 Chevrolet Avalanche 1500; 2006 Chevrolet Kodiak, Chevrolet Suburban 1500; GMC Topkick 6500. A loose engine fuel-rail pulse damper can cause a fuel leak, posing a risk of a fire. Dealers will replace the damper retainer clip for free. For more information, call Chevrolet at (800) 630-2438 and GMC Trucks at (866) 996-9463.