THE DRIVE TO SURVIVE In a study of German motorists that gives new meaning to the concept "killer commute," researchers conclude that people caught in traffic are three times more likely to suffer a heart attack within the hour than those not tied up on the road.

A study of hundreds of heart attacks in southern Germany published in last week's New England Journal of Medicine found nearly one in 12 attacks was linked to traffic. Traffic jams were more likely to take a toll on women and on people 60 and older.

Why the increased risk? Nobody's sure. "Given our current knowledge, it is impossible to determine the relative contribution of risk factors such as stress and traffic-related air pollution," wrote the researchers.

The study was based on interviews with 691 heart attack survivors who were asked to outline their activities during the four days before their attack.

Traffic posed a risk regardless of the mode of transportation. Heart attacks were 2.6 times more common among those who had been stuck in cars shortly before the cardiac event than among those who hadn't, 3.1 times higher for people stalled in traffic while taking public transportation, and 3.9 times greater for those jammed up on a bike.

YES, SIZE MATTERS Men who weigh too much are more likely to have poor sperm quality, research on nearly 1,600 Danish men has found. Being too thin is a problem, too.

The study, published in the October issue of the journal Fertility & Sterility, involved 1,558 men, average age 19, who volunteered to give a semen sample.

Sperm counts, sperm concentration, semen volume and other measures of sperm quality such as shape and motility were measured, along with testicle size and hormone levels. Researchers also calculated each man's body mass index, or BMI, a measure of obesity that takes into account height and weight.

Scores for men with healthy BMIs -- 139 to 174 pounds for a man who is 5-10 -- were compared to those of men above and below that range.

Sperm counts and sperm concentration were 21.6 percent and 23.9 percent lower in overweight men than in healthy-weight men. The same measures were 28.1 percent and 36.4 percent lower in underweight men.

Why this may be happening is unclear. Men produce and need a certain amount of the female hormone estrogen. Fat cells produce estrogen, so too much or too little of it may be a problem.

"It's not uncommon for a man to come in after his wife has had a million tests" and be discovered to have sperm problems, the researchers said. "It's probably one of the first things a doctor should do."

-- From News Services and Staff Reports