CHECKUP : NEWS, TIPS AND TRENDS RESEARCHERS CONTINUE TO QUESTION MELATONIN'S EFFECTS.

A week after government researchers said that the public should avoid using melatonin - the popular supplement that has been promoted to help people sleep and overcome jet lag - British researchers now report that the hormonal supplement disrupts, rather than aids, sleeping rhythms.

In a new study of 10 healthy men in their 20s who were kept in a closed environment and allowed to follow their normal sleep patterns, some experienced disturbed sleeping rhythms after taking melatonin, reported lead author Dr. Benita Middleton of the University of Surrey in Guildford, England.

Sleep patterns returned to normal soon after the men stopped taking melatonin, which is sold under the name ``Rapi-snooze'' in Britain, she reported in the medical journal the Lancet.

Just last week, U.S. researchers at a National Institutes of Health-sponsored meeting in Bethesda, Md., advised against self-medicating with melatonin, saying that the hormone pill may cause adverse effects, including nightmares, nausea and increased levels of depression.

And now, with the new report, ``it is clear that indiscriminate use of melatonin could lead to undesirable effects,'' Middleton said.

Melatonin, a hormone produced by the pineal gland that lies in the brain, is thought to be involved in the normal daily rhythms of the body. Melatonin is mostly made at night, so people have assumed that taking extra quantities of the hormone will help them sleep.

Headed for heartburn: A new study says heartburn is linked to people's lifestyles and activities. Sufferers reported symptoms triggered by skipping meals, worrying, traveling frequently for business, changing jobs, or spending less than two hours a day relaxing by reading or watching television, says the study conducted for the New York Hospital-Cornell Medical Center.

Electric detection: A new test for electrical changes in the mouth may enable earlier detection of mouth cancers without repeated painful biopsies, Maryland researchers say.

Investigators are using a chemical battery and a probe to noninvasively measure the electrical charge of the surface tissue of the mouth, said lead investigator Dr. Paul Castellanos, an otolaryngologist at the University of Maryland Medical Center.

Castellanos said that normal mouth tissue gives off electrical readings that are much higher than readings from abnormal or cancerous tissue. Other studies have shown similar changes with gynecological, skin and breast cancers.

The electrical charge is recorded on a voltmeter, he said, adding that the test may one day provide a reliable method for identifying and following precancerous changes in the mouth without repeated tissue biopsies.

Forecasting ozone: For you sunbathers, good news is blowing in the wind. Changes in the winds high over Hawaii may offer an opportunity to predict low ozone levels that could endanger people exposed to the sun. Record low amounts of ozone measured by the Mauna Loa Observatory in Hawaii in late 1994 appear to be the result of a reversal of wind direction in the upper air, says a paper in the journal Geophysical Research Letters. These winds change direction every 26 to 32 months, so by tracking the changes, scientists should be able to anticipate unusually low ozone levels.

Breathe easier: Plastic credit cards imprinted with self-management instructions for asthma reduce both the number of asthma attacks and emergency-room visits, New Zealand researchers report.

Individualized instructions on what self-management steps to take, such as when to take your medication and what medication to take, as well as when to seek professional help are printed on each card.

The program was created because so many high-risk adult asthma patients are known to neglect to take their medications, and often end up being seen in the emergency room, said asthma specialists at the Wellington School of Medicine in New Zealand.

But when 26 high-risk adult asthma patients carried credit cards with self-management instructions, the number of participants waking with asthma symptoms more than once a week dropped from 65 percent to 23 percent, the researchers reported. The number of visits to the emergency room decreased from 58 percent to 15 percent.

Alternative to surgery: Surgery that removes the voice box is no longer the only choice for treating most throat cancers, according to experts who say chemotherapy now has been proven just as effective against the disease. Their study, conducted by the European Organization for Research and Treatment of Cancer, was published in the Journal of the National Cancer Institute.

Midwives deliver: Midwives may be making a comeback, if the results of a British study are any predictor of future trends.

The study, in which nearly 1,300 healthy pregnant women were randomly assigned to either a midwife or a physician, found that women whose babies were delivered by midwives had fewer complications and a higher satisfaction rating, said Deborah Turnbull of the Glasgow Royal Maternity Hospital.

``We conclude that midwife-managed care for healthy women, integrated within existing services, is clinically effective and enhances women's satisfaction with maternity care,'' she reported in the British medical journal the Lancet.

Turnbull said the results of the study should encourage other maternity units to develop research programs to evaluate midwife-managed care in a range of clinical settings.