Uncontrolled high blood pressure may be responsible for a quarter of the first heart attacks in older Americans, a new national study suggests.

Researchers tracked nearly 5,000 men and women over age 65 for about five years to see which were most likely to have a heart attack. None of the patients had suffered a heart attack when the study began.

While smokers were more likely than nonsmokers to have a first heart attack after age 65, smoking was not as strong a risk factor as high blood pressure or abnormally elevated blood sugar, a sign of diabetes.

The risk of a first heart attack was higher in men than in women, the study found, and it increased with advancing age. Presence of clinical cardiovascular disease, as shown by a thickening of the carotid artery in the neck or an abnormal reading on an echocardiogram, a test of the heart's pumping ability, also were linked to a greater chance of heart attack.

"In this population, elevated levels of blood pressure and glucose clearly pose the greatest hazard to the health of the public," researchers concluded. A systolic blood pressure over 140 may explain one-fourth of the heart attacks in the study, they said. Systolic blood pressure--the pressure of blood flow immediately after the heart beats--is the first of two numbers commonly used to express a given level of blood pressure, as in "140 over 90."

Researchers said the findings show that "treatment of even modest levels of systolic hypertension and the prevention of [diabetes] with diet and physical activity are likely to have the largest effects in preventing the incidence of coronary disease in older adults."

Within five years, about 6 percent of the people in the study--302 in all--had "coronary events," including 263 heart attacks, 29 of which were fatal. Thirty-nine other people died of "definite fatal coronary heart disease."

The study, by a team of cardiovascular specialists from seven medical centers, was funded partly by the National Heart, Lung and Blood Institute. The results appeared last week in the Archives of Internal Medicine.

--Don Colburn


Human beings, in common with animals, plants and even single-celled organisms, have a precise biological clock that keeps their body functions in synch with the Earth's 24-hour rotational period, and that time-keeping mechanism doesn't lose accuracy as we get older.

Those conclusions, from a new study by Harvard researchers, contradict two widely held beliefs drawn from earlier research: that the "natural" human cycle was closer to 25 hours, and that the cycle length tended to shorten as people aged.

Many people report a change in sleep patterns with age--including a tendency to wake up earlier and a higher incidence of sleep problems--and those phenomena have often been blamed on an age-related change in the body's time-keeping mechanism. But now researchers will have to seek some other explanation for sleep disturbances in the elderly.

In 13 healthy older men and women (average age 67) in the new study, the biological clock cycled about every 24 hours and 11 minutes, exactly the same period found in 11 healthy men whose average age was 24. "This is a remarkable discovery: an important human function that does not deteriorate with age," marveled University of Pittsburgh neurologist Robert Y. Moore, in a commentary that accompanied the Harvard study in the June 25 issue of Science.

A team led by Charles A. Czeisler, director of circadian medicine at Boston's Brigham and Women's Hospital, kept the 24 participants sequestered for a month and tried to eliminate all cues that might have revealed the time of day. Their lives during the study were scheduled according to a 28-hour "day," and nine-hour sleep periods were allowed at times that varied from one day to the next. Napping was forbidden. Also, lighting was kept deliberately low during activity periods to avoid resetting the brain's clock.

The researchers continuously monitored the participants' core body temperature and measured blood levels of two hormones--cortisol and melatonin--multiple times each day. All three are known to rise and fall in a diurnal pattern. They found that body temperature and the two hormones varied according to exactly the same 24-hour cycle, strong evidence that the brain's biological clock was controlling all three.

Other research has located the clock in the suprachiasmatic nucleus (SCN), a collection of nerve cells in the hypothalamus, a structure at the base of the brain. Cells of the SCN, which receive input from the eye's retina, rhythmically signal other areas of the brain, determining the sleep-wake cycle and the temporal pattern of other body functions.

Czeisler said the elderly, despite having an accurate internal clock, probably have a narrower "window of opportunity" for sleep than the young because they sleep less deeply and can't help waking up as soon as the SCN signals that morning is coming.

"The ability to sleep at a phase other than that when the circadian pacemaker is promoting sleep is remarkably reduced in older people," he said.

--Susan Okie


A much-feared heart condition called mitral valve prolapse is less common and less serious than previously believed, according to a large new study.

Using an improved form of ultrasound test, researchers examined the hearts of nearly 3,500 people and found mitral valve prolapse in only 84, or slightly more than 2 percent. Most previous estimates of the condition's prevalence had ranged from 5 percent to 15 percent, with some reaching as high as 35 percent.

Among the 84 patients with mitral valve prolapse, rates of complications such as stroke and heart failure were no higher than in the general population, the new study found.

Mitral valve prolapse is a condition in which a heart valve is abnormally long and floppy. In some patients this can allow blood to leak back into the heart, forcing it to work dangerously hard.

"The low frequency of complications in our study may alter the perception of the severity of the disease and allay anxiety for those in whom mitral valve prolapse is diagnosed in a general population," researchers concluded.

Their results, based on the National Heart, Lung and Blood Institute's ongoing Framingham Heart Study, were reported last week in the New England Journal of Medicine. Claude Lenfant, director of the NHLBI, called the findings "compelling" and suggested that patients diagnosed with mitral valve prolapse consult their doctors to see whether they should be rechecked.

The new data, along with advances in diagnosis and repair of the more serious forms of mitral valve prolapse, "will help us avoid the panic that was previously associated with this diagnosis," wrote two doctors from the Mayo Clinic in an accompanying editorial.

Diagnosis of mitral valve prolapse increased sharply about 20 years ago after ultrasound tests allowed doctors to inspect the heart without surgery or invasive tubes. The new estimates are based on studies with a refined type of echocardiography designed to minimize the inaccuracy of the earlier tests.

--Don Colburn