Both asthma and obesity are becoming increasingly common in the United States. The latest research to examine relationships between the conditions finds that obesity is a risk factor for repeated hospital visits in children with asthma.

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Obesity, asthma, and hospitalization are explored in a new study.

In the U.S., the percentage of children with obesity “has more than tripled since the 1970s.” Between 2011 and 2014, around 17 percent of children and adolescents aged 2–19 were obese.

Asthma is also becoming more common. In 2001, around 1 in 14 adults had asthma — but by 2009, that number had increased to 1 in 12. This means that in the U.S., around 25 million people have asthma.

This sharp rise applies to children, too; in 2009, around 1 in 10 children had asthma. The biggest increase was measured in black children, who experienced an almost 50 percent increase from 2001 to 2009.

In recent years, links between obesity and asthma have become clear. Studies show that obesity makes the symptoms of asthma worse, and, to add insult to injury, obesity seems to make some asthma drugs — such as inhaled corticosteroids — less effective.

Although asthma is more common in obese people, the exact cause and effect relationship is not yet fully understood. However, it seems that obesity increases the likelihood of developing asthma, makes symptoms worse, and hinders treatment.

A number of studies have looked at the relationship between obesity, severity of symptoms, and time spent hospitalized. However, many of the studies were inconclusive. Also, to date, the interplay between obesity, asthma, and hospitalization has not been examined in children.

A group of scientists from Japan recently set out to investigate whether or not obesity affects the likelihood of repeat hospital admissions and the length of stay in the hospital in a pediatric population.

They also wanted to understand the impact on healthcare costs and the risk of intensive care. Their findings were recently published in the journal Pediatric Allergy and Immunology.

The researchers were led by Yusuke Okubo, from the Department of Social Medicine at the National Research Institute for Child Health and Development in Tokyo, Japan.

They analyzed the hospital discharge records of patients aged 3–18 between July 1, 2010, and March 31, 2015. The data came from more than 1,000 Japanese hospitals.

Information regarding diagnosis, pre-existing conditions, age, sex, weight, and height were noted for each patient. Children with chronic medical conditions — endocrine, pulmonary, or neurologic diseases, for example — were excluded. Only children who were repeatedly hospitalized were used in the analysis.

In total, 38,679 patients were involved in the study. Of these, 3,177 were underweight, 28,904 were normal weight, 3,334 were overweight, and 3,264 were obese. Obese patients were more likely to be male, older, and have allergic rhinitis than the other weight groups.

Those in the obese group had a significantly (26 percent) higher risk of being readmitted to hospital within 30 days compared with normal-weight children.

Obese children also stayed, on average, an extra 0.12 days in hospital. However, there were no differences in the need for intensive care.

No statistical differences between hospitalization costs across the weight categories were found. U.S. studies have previously found evidence of such a relationship, but the authors of the current study believe that this may be due to “different payment and insurance systems between the U.S. and Japan.”

Overall, they conclude:

Our findings demonstrated that even in children, obesity was also associated with an elevated risk of readmission. These results suggest that obese children require more attention and greater treatment to control their asthma after discharge from hospital.”

Because obesity and asthma are both linked and both on the rise, there is likely to be more focus on research in this area. The findings underline yet another reason to work toward stemming the tide of obesity in the U.S.