Could Obesity Contribute to Asthma?
WHY YOU SHOULD CARE
Because if obesity does contribute to asthma, treating asthma might be just as much about keeping our weight in check.
Eric Garner, a 43-year-old father of six, was arguing with the police when they wanted to arrest him for hawking untaxed cigarettes in front of a Staten Island beauty supply store in July. At least five officers took him down, one pinning him in a chokehold. “I can’t breathe! I can’t breathe!” the 350-pound lifelong asthma sufferer shouted again and again. One witness claimed to see him foaming at the mouth. He died a few minutes later. Medical examiners reported that obesity, asthma and heart problems contributed to his death.
Doctors could start ”paying more attention to diet … like what we do for heart disease.”
Besides the race and class issues, the tragedy also raises a medical and public health question: Why do so many obese individuals also suffer from asthma? In 2010, nearly two-fifths of adults with asthma were also obese, according to the Centers for Disease Control and Prevention. Meanwhile, children who carry excess weight are up to 1.37 times more likely to develop asthma than normal-weight kids.
Although scientists know obesity and asthma often occur hand in hand, they have yet to unravel the connection between them. It’s a classic chicken-or-egg riddle. Some argue that asthma constricts the airways, making it tougher to exercise and easier to gain weight.
African-American children have an 80 percent higher rate of asthma and are nearly three times more likely to die of the condition than white children.
But researchers at Massachusetts General Hospital, Harvard Medical School and Boston Children’s Hospital suspect that causation might go in the other direction — that obesity contributes to asthma. Several studies suggest that fat tissue squeezes on the airways and even secretes proteins that trigger wheezing, coughing and other symptoms, as outlined in a recent Annals of Allergy, Asthma & Immunology review article.
If that’s true, asthma treatment and management plans could change to include keeping obesity in check. Doctors could start “paying more attention to diet … like what we do for heart disease,” says Dr. Meyer Kattan, professor of pediatrics at Columbia University Medical Center (CUMC). A causal link might also galvanize public health measures to fight obesity, like widening access to parks and fresh produce in low-income communities of color, where both asthma and obesity run rampant.
Doctors might also need to be more careful about prescribing medications. Some studies suggest that the mechanisms underlying obesity-associated asthma differ from those of other types of asthma. That may explain why many obese patients don’t respond to steroidal drugs like prednisone — which also trigger weight gain.
And asthma is only one among a slew of health problems linked to obesity, rates of which have more than doubled since the 1970s. As obesity rates surge, knowing how to treat people with multiple conditions — without alleviating one at the expense of another — is more crucial than ever.
But of course, more research is needed. Asthma sets in when the immune system reacts to noninfectious agents, like mold or pet dander, triggering inflammatory responses that result in wheezing and a phlegmy cough, for example. Although a link between asthma and obesity exists, some of the data conflict, and “we don’t know the full connection,” which is most likely the result of a complex tangle of factors, says Dr. Wanda Phipatanakul, a specialist in allergy and immunology at Boston Children’s Hospital, who co-authored the review article.
A number of findings have clued scientists into the possibility that obesity might contribute to asthma. For example, a 2011 University of Michigan study found that obese individuals with asthma relied less on asthma medication after bariatric surgery. And CUMC researchers have observed that both obesity and anorexia can lead to asthma, leading them to suspect that fat cells are somehow signaling to the lungs.
Some suspect that this crosstalk could begin early, even in utero — a critical period with long-term, irreversible consequences for the growing fetus. A study published in Pediatrics last month found that the children of women who were overweight or obese during pregnancy had up to a 20 to 30 percent higher risk of developing asthma. Although it’s not clear why, the researchers note that fat cells secrete inflammatory proteins that might affect lung development.
Fat tissue also secretes proteins that can boost the immune response and potentially trigger asthma symptoms.
Obesity can also weigh on the lungs — literally. Excess fat might constrict the chest wall, reducing lung function. Dr. Gerard Karsenty, a professor of medicine at CUMC, led a study published in Cell Metabolism last year suggesting that a hormone secreted by fat cells, called leptin, modulates airway diameter by regulating the parasympathetic branch of the nervous system (PNS). When scientists administered a drug that inhibits the PNS to obese and asthmatic mice, their airways opened up and their symptoms abated, suggesting that scientists could develop a similar medication for humans.
Leptin may be involved in other aspects of the obesity-asthma relationship, because it could trigger inflammatory responses characteristic of asthma. Kattan’s 2010 study of 368 adolescents with moderate to severe asthma in 10 inner-city areas correlated higher levels of body fat (and leptin) with poorer asthma control in female participants. But the findings remain debatable; a 2013 American Journal of Respiratory and Critical Care Medicine study saw no difference in leptin in obese and normal-weight kids with asthma.
Phipatanakul thinks any number of these factors could explain how obesity might contribute to asthma. At this point, “it’s hard to know. I assume that, as in most diseases, it’s multifactorial,” she says. “There’s a lot of interest in this topic, but it’s not fully understood.” Tackling asthma might be a matter of turning multiple dials, versus simply flipping a kill switch.