NEW YORK (Reuters Health) - Kids with diabetes may have a higher-than-average rate of asthma, and those with both conditions seem to have a tougher time keeping their blood sugar under control, a study out Monday suggests.

Researchers found that among 2,000 3- to 21-year-olds with diabetes, 11 percent had asthma -- higher than the roughly 9 percent rate among children and young adults in the U.S.

The difference was bigger when the researchers looked at the 311 young people with type 2 diabetes, the form associated with obesity and usually diagnosed in adults.

In that group, 16 percent had asthma, compared with 10 percent of those with type 1 diabetes.

Type 1 diabetes is caused by an abnormal immune system reaction that kills off the pancreatic cells that make insulin, a hormone that helps shuttle sugar from the blood and into body cells to be used for energy. People with the disease have to take shots of synthetic insulin (or use an insulin pump) every day to keep their blood sugar levels normalized.

In this study, kids with both type 1 diabetes and asthma were more likely to have poor blood sugar control than their peers who were asthma-free: 15.5 percent, versus 9 percent.

"Poor" blood sugar control meant having a hemoglobin A1C level of more than 9.5 percent. Hemoglobin A1C is a measure of long-term blood sugar control, and experts say it should be kept below 7 percent in adults, while children's can go as high as 8.5 percent depending on their age.

The reasons for the findings, which appear in the journal Pediatrics, are not completely clear.

But the higher rate of asthma among young people with type 2 diabetes suggests a role for obesity, according to lead researcher Mary Helen Black, of the department of research and evaluation at Kaiser Permanente Southern California.

"It's pretty well-established that there's an obesity-asthma connection," Black told Reuters Health in an interview.

As for why young people with type 1 diabetes and asthma had poorer blood sugar control, one possibility is that there is a "real biological connection," Black said.

Some past research, for example, has found that people with poorly controlled diabetes are more likely to show dips in lung function over time than those with well-controlled diabetes. But the reasons for that are unknown.

On the other hand, Black said, it may simply be tougher for kids with type 1 diabetes to control their blood sugar when they have another chronic health problem.

"It can be incredibly challenging to manage both conditions," Black said.

The researchers did find that when kids with both diseases were on asthma medication, their blood sugar control was better.

In particular, poor blood sugar control was seen in less than 5 percent of those taking asthma drugs called leukotriene modifiers (sold under the brand-names Singulair, Accolate and Zyflo).

That compared with about 30 percent of type 1 diabetics who were not on medication for their asthma.

The researchers are not sure if that means there's an effect of the asthma drugs themselves. It may just be that kids with better-controlled asthma are also more likely to have well-controlled diabetes, according to Black.

She said the bottom line for doctors and parents is to be aware that kids with diabetes may have a somewhat higher rate of asthma -- and that those with both may have more trouble with blood sugar control.

If parents notice potential signs of asthma -- like wheezing, coughing or breathing problems that are not related to a cold or other infection -- they should talk to their child's doctor, Black said.

SOURCE: http://bit.ly/pTAIqi Pediatrics, online September 26, 2011.