That may be one more health reason to lose extra pounds, note the researchers.
They included E. Rand Sutherland, MD, MPH, who works in Denver at the National Jewish Medical and Research Center and the University of Colorado Health Sciences Center.
Together, the studies included more than 333,000 adults in the U.S., Canada, and Europe.
Participants reported their height, weight, and whether or not they had asthma. The researchers calculated participants' BMI (body mass index), which relates height to weight.
A BMI of 30 or higher is considered obese. A BMI of at least 25 but less than 30 is considered overweight.
Sutherland's team pooled data from all seven studies. They found that, compared with participants with normal BMI, asthma was 38% more common in overweight adults and nearly twice as common among obese adults.
But Sutherland and colleagues aren't blaming asthma solely on weight. Many factors affect asthma risk.
Sutherland's team also doesn't promise that losing extra weight will prevent asthma.
Asthma affects people of all shapes and sizes. Thinness is not a guarantee of health. None of the reviewed studies test the theory that losing extra weight makes asthma less likely.
Some participants may not have reported their weight and height accurately, and some may have mistakenly thought they had asthma, note Sutherland and colleagues.
The review appears in the American Journal of Respiratory and Critical Care Medicine.