CHICAGO (Reuters) - Being fat may increase the risk of developing asthma, perhaps because obesity compresses the airways, according to two studies released on Sunday. One report from Harvard Medical School in Boston involved 100,000 nurses in the United States who were tracked for five years. The researchers found that those in the group who were the most obese when the study began were three times more likely to have developed asthma over the study period as those who were the least overweight. In a second study British researchers traced the relation between weight at birth and weight and asthma prevalence at age 26 in more than 8,000 people. That study from United Medical and Dental Schools in London found that the heaviest adults were 80 percent more likely to have asthma than the slimmest ones. But at the same time low birth weights were associated with the development of asthma later in life. Carlos Camargo, who led the Harvard study, said very little research had been done linking asthma to obesity. But extra weight could somehow compress the airways, making them smaller and more reactive to cold or other conditions that can trigger asthma. Other researchers have suggested over the years that obese people tend to exercise less and as a result their lungs don't get the asthma-lessening effect that exercise is believed to provide. Both asthma and obesity are on the rise in developed countries. In the United States the rate of asthma rose 61 percent from 1982 to 1994. In another study presented at the meeting German researchers suggested that students who snore are more likely to do poorly on their exams. The study involved about 200 medical students who were taking final exams in internal medicine. The researchers said they made the study because of previous research showing that middle-aged men who snore are often sleepy during the day and have work-related difficulties as a result. They said they wanted to find out if there was a similar effect among younger people.