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Does obesity increase risk of childhood asthma?

Rates of childhood asthma are going up and researchers have identified a surprising (and preventable) culprit. @NightshiftMD has the details.
In a study published in the journal Pediatrics, researchers found that 23 to 27 per cent of new cases of asthma in the children were directly attributable to obesity. (Shutterstock)

Rates of asthma are on the rise in children, and doctors have struggled to figure out why.

A study just published in the journal Pediatrics has identified a new cause — one that's both preventable and reversible.

The cause appears to be childhood obesity.

Researchers at children's hospitals in Delaware and Florida analyzed the health records of more than half a million children ages two to 17. None had a prior history of asthma. The researchers matched children of normal weight with kids who were overweight or obese. Other than weight, all other characteristics of the children were similar.

The researchers found that the chance that a child was diagnosed with asthma was significantly greater if the child was obese. They found that 23 to 27 per cent of new cases of asthma in the children were directly attributable to obesity.

They also found a link between being overweight and having asthma. However, the link between overweight and asthma was not as strong as was the link to asthma in kids with obesity.

According to the Centers for Disease Control and Prevention (CDC), weight that is higher than what is considered as a healthy weight for a given height is described as overweight or obese. Body Mass Index, or BMI, is used as a screening tool for overweight or obesity. 

The connection is not well understood, but there are some theories. One is that carrying extra weight around the chest might predispose children to asthma by narrowing the airways or restricting the chest to shallow breaths. Studies have shown that obesity reduces the volume of air that can be inspired into the lungs.

Another hypothesis is that adipose or fatty tissue releases chemicals called adipokines that increase inflammation inside the body. The "excess" inflammation caused by adipokines makes the airways more sensitive to environmental triggers like cat and dog dander that can set off asthma attacks.

Another theory is that obesity triggers a third condition such as acid reflux and obstructive sleep apnea that in turn trigger asthma. None of these have been proven.

The prevalence of asthma has also been shown to be higher in adults who are obese. (M. Spencer Green/Associated Press)

Role of obesity

Researchers say the results are plausible. The prevalence of asthma has also been shown to be higher in adults who are obese.  Other studies have shown that obesity increases the incidence of asthma by at least two-fold in children and adults. This study found that obesity didn't just increase the rate of asthma. It also increased its severity. The higher the body mass index, the more severe the asthma.

Another factor that makes this study so credible is that it used big data analysis to examine a huge pediatric population. Other studies haven't been large enough to detect differences between ethnic groups and other potential risk factors.

Some researchers believe the connection between obesity and asthma is just a coincidence of two common conditions. In the U.S. 18.6 per cent of children are obese, and more than eight per cent have asthma. Some believe asthma is the result of obesity rather than the cause. A study published in 2017 found that children diagnosed with asthma are more likely than children without asthma to become obese.

The authors of the study in Pediatrics say that as many as eight million children in the U.S. have been diagnosed with asthma. If the findings of the current study are correct, a million of those cases of asthma (12.7 per cent) might be directly attributable to being obese and (to a lesser extent) being overweight. They say at least 10 per cent of all cases of asthma in childhood in the U.S. might be prevented if obesity and overweight in childhood were avoided.

Currently, there are few known prevention factors that can be used to reduce childhood asthma. Reducing obesity would be good for children. It would also reduce significantly the burden of asthma and obesity on the health-care system.

The obvious recommendation is weight loss. Studies have shown that overweight and obese adults with asthma who lose weight have significant improvements in asthma control.

Losing weight improves the symptoms of asthma. One researcher called weight reduction a cornerstone in the management of obese patients with asthma.

That's treating obesity. The goal should be avoiding it in the first place. Knowing that there's a strong link between obesity and asthma in children is one more reason to try and prevent both.

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