SUNDAY, March 20 (HealthDay News) -- People with asthma may have a higher risk of developing diabetes and heart disease, according to a new study that looked at the relationship between asthma and four other inflammatory conditions.

The study, which looked at medical records from the late 1960s through the early 1980s, found higher rates of diabetes and heart illness among asthmatics than other people.

Researchers led by Dr. Young J. Juhn, of the department of pediatric and adolescent medicine at the Mayo Clinic in Minnesota, found that people with asthma were not at greater risk of developing inflammatory bowel disease or rheumatoid arthritis, but Juhn said that was likely due to the small sample size. "The trend was in a positive direction for all four proinflammatory conditions," he said.

One expert said the results were unexpected because asthmatics have a different immune system profile from cardiac and diabetes patients.

"It was surprising because there are two broad categories (of immune profiles) that they're looking at here," explained Dr. Jennifer Appleyard, chief of allergy and immunology at St. John Hospital and Medical Center in Detroit.

One type of profile is more common to people with asthma, and the other more common to those with inflammatory diseases such as arthritis and coronary heart disease, she said. Appleyard noted that, in theory, a person prone to asthma should not be prone to diabetes.

She believes that the study findings should be seen as preliminary and more research is needed to understand the relationship.

"It's important to look at how they (asthma, and diabetes or heart disease) interact or affect each other, both looking at possible causes and risk factors, and then specific treatment geared to that part of the immune system," Appleyard said.

In background materials for the study, lead author Juhn noted that although people with asthma have a more allergy-prone immune profile, it is balanced by a counter-regulatory one known as the Th1 immune profile, which underlies proinflammatory conditions such as coronary artery disease and diabetes. He speculated that there might be "an inverse relationship" between asthma and those types of proinflammatory conditions.

The findings were slated to be reported Sunday at the annual meeting of the American Academy of Allergy, Asthma & Immunology in San Francisco. Experts note that findings presented at medical meetings do not undergo the strict peer review of studies published in reputable journals.

Asthma, a chronic lung condition that can range from mild to severe, affects close to 25 million Americans ranging from newborns to elderly adults, according to the study. Symptoms include difficulty breathing, tightness in the chest, coughing and wheezing. The underlying cause is unknown but the illness can be triggered by allergies, exercise or environmental contaminants such as chemical fumes or dust. About 70 percent of asthmatics have allergies.

The new study looked at medical record of almost 2,400 subjects with asthma and a control group of 4,784 people without asthma from 1967 to 1983, matching asthmatics with non-asthmatics for gender and age.

The average age of onset for the condition was 15 years. The vast majority were white and 57 percent were male.

The study found that among asthmatics, about 138 people per 100,000 had diabetes, compared to 104 for people without asthma; the rate for coronary heart disease was close to 189 per 100, 000, versus 134 among non-asthmatics.

But one asthma specialist said that the retrospective nature of the study was "important to consider" because looking at old records is not the most effective way to get data.

"It would warrant a prospective study to find patients with asthma now and follow them to see what happens," said Dr. Linda Dahl, an ear, nose and throat specialist and surgeon at Lenox Hill Hospital. "It would be important to assess both the disease and treatment, and how that affects what other illnesses develop."

The study also looked at patients from the 1960s through the 1980s who did not have access to many medications available today, she noted. Treatment 40 years ago was very "steroid heavy," which could have contributed to weight gain -- a known risk factor for diabetes and heart disease, Dahl said.

"Sometimes treatment can be part of the problem," she said.

Nowadays, medications such as long-acting beta agonists (LABAS) and corticosteroids can prevent flare-ups. Drugs like albuterol, and oral and intravenous corticosteroids, are taken for sudden attacks. Anti-allergy medications are also used to prevent bouts of the disease over time.

But Dahl also said she noticed that many of her asthma and allergy patients had other inflammatory diseases such as arthritis and irritable bowel syndrome. However, "it is hard to know if one is causing the other, or if they are just found together," by coincidence, she said.

Asthma can prove deadly on its own, of course. According to the American Academy of Allergy, Asthma and Immunology, close to 3,400 deaths from asthma occurred in 2005.

"It's a wildcard," said Appleyard, noting that asthma-related deaths occur equally among those who have mild, moderate or severe cases.

More information

Find out more about asthma at the U.S. National Heart, Lung and Blood Institute.