The link between asthma and being very overweight is not well understood. Does obesity cause asthma? Or are they two separate conditions that co-exists in some people? The answer might be both.
Several different types of research suggest the two conditions are related. Studies of the population show that rates of obesity and asthma increased together.1 Clinical studies have shown that extra body weight can change the way the lungs function.2 It also causes changes in the immune system and inflammatory signals in the body.2,3
New research suggests that there may be different types of obesity-related asthma with different causes.4,5 For example, obesity may cause a type of non-allergic asthma that starts in adulthood. In other cases, allergic asthma may start in childhood and get worse because of obesity.
Am I obese?
Your BMI (body mass index) is simple way of estimating body fat. It is calculated based on your height and weight. Your BMI is used to tell if you are underweight, normal weight, overweight, or obese.
For adults, the National Heart, Lung, and Blood Institute has an online BMI calculator. The BMI categories for adults are:
- Underweight: BMI less than 18.5
- Normal weight: BMI between 18.5 and 24.9
- Overweight: BMI between 25 and 29.9
- Obese: BMI of 30 or higher
These cut-off points are not used for children and teens. In children and teens, weight is evaluated based on BMI percentiles or BMI-for-age. A child’s BMI is compared with other children the same age and gender. A BMI calculator for children and teens is available on the website for the Centers for Disease Control and Prevention.
- Underweight: BMI-for-age less than 5th percentile
- Normal weight: BMI-for-age between 5th and 85th percentile
- Overweight: BMI-for-age between 85th percentile and 95th percentile
- Obese: BMI-for-age above 95th percentile
How does obesity affect asthma?
People—especially adult women—who are obese are more likely to develop asthma.2,3 Children and adults who are very overweight are more likely to have persistent (ongoing) asthma and more severe asthma.3 Typical asthma control medications do not work as well in people who are obese.2,5
Some symptoms of obesity overlap with asthma symptoms, making diagnosis difficult. Obesity is linked with lower fitness and feeling breathless. People who are obese are more likely to have GERD (gastroesophageal reflux disease), which can cause coughing and chest tightness that is confused with asthma. Obesity is also a risk factor for sleep apnea, which can be difficult to distinguish from asthma.2,3
How common are comorbid asthma and obesity?
In the United States, 16.9% of children and 34.9% of adults are obese.6 About 8% of people younger than 15 years and 7.2% of people older than 35 years have asthma.7 Research has shown that obese adults are 1.6 to three times more likely to develop asthma.1 The effect of childhood obesity on asthma is less clear.1
How is obesity treated?
The primary treatment for obesity is weight loss. Weight loss can be achieved through diet changes and increased exercise. One study showed that 5% weight loss is enough to improve asthma control.2 For some people who are morbidly obese, bariatric surgery may be an option.
Exercise is recommended for its general health benefits, as well as for weight loss. Exercise is a common trigger for asthma symptoms.8 Your health care provider or respiratory therapist can work with you to develop an exercise program and manage your symptoms. Typically, this involves using a short-acting beta-agonist (SABA) before exercise and doing a ten to 15 minute warm up.9
What effect does treating obesity have on asthma?
It seems logical that weight loss might improve asthma control, although few studies have been done to prove it.2 Studies do show that adults who lose weight have better lung function, fewer asthma flare-ups, and need less medication.3
Reported results after bariatric surgery have been impressive, although the studies are not very high quality.1 About half of people no longer have asthma after the surgery. Up to 90% need less medication and have fewer asthma attacks or hospitalizations.