A Weighty Issue for Those With Asthma
Researchers Find Obesity Is Associated With Asthma By Gregory Alford If you need one more compelling reason to put down the donuts and exercise more to drop those extra pounds, you now have it. Researchers are making a strong case for a link between obesity and asthma.
The question is far more than an academic curiosity. The Centers for Disease Control and Prevention (CDC) and many physicians define clinical obesity as having a body mass index (BMI) of 30 or higher (see
sidebar.) According to the CDC, 63.1 million Americans over the age of 20 are clinically obese. An additional 71.7 million are clinically overweight, which is a BMI rating of 25 to 29.
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“Assuming a prevalence of obesity of 30% among U.S. adults and estimates of relative risk ranging from 1.6 to 3.0, [this] suggests that about 15% to 38% of asthma in adults might be caused by obesity and thus might be preventable,” says Earl Ford, MD, of the Centers of Disease Control and Prevention (CDC) in Atlanta. Children and adolescents are not faring any better in the battle of the bulge. The CDC reports the number of overweight children, ages 6 to 11 years old, increased 376% between 1965 and 2002. During the same years, the number of overweight adolescents age 12 to 19 years old increased by 350%. Also during this period, dramatic increases have occurred in the rate of asthma in the United States. The CDC reports that 20.3 million people in the US currently report having asthma, 9 million of them children. The number of people who report having asthma increased 75% from 1980 to 1994.
Current Research Trends In years past, the assumption was that many asthmatics were obese because their physical limitations caused or contributed to their weight gain. However, recent studies suggest chemical changes in the body caused by obesity may be contributing to the increase in the incidence of asthma. Current areas of investigation include: • Increased physical stress caused by excess weight may reduce lung capacity (J Appl Physiol 1995;79:1199-1205). • The obese take additional, shallower breaths than people of normal weight. This increases airway responsiveness to allergens and other asthma triggers, and narrows the airways (J Appl Physiol 1983;55:1269-1276). • Carrying too much body weight causes an increase in the production of certain compounds that result in low-grade inflammation, which increases the risk of asthma, type 2 diabetes and cardiovascular disease (J Allergy and Clin Immun 2005;115:925-7). Although researchers are making headway, they still have more questions than answers about the link between obesity and asthma. “Obesity has the capacity to impact lung function in a variety of ways,” says Jeffrey Fredberg, professor of bioengineering and physiology at Harvard University in Cambridge, Massachusetts. “None of them are good and all of them are poorly understood. More research is needed to explain the relationship between asthma and obesity.”
Obesity’s Role in Asthma: What the Research Shows A plethora of studies show clinically obese children are more likely to be asthmatic than children of average 18
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ASTHMA MAGAZINE
July/August 2005
weight. In one study, Loreto G. Sulit, MD, of Rainbow Babies and Children’s Hospital at Case University School of Medicine in Cleveland, led a research team that studied medical records of 788 children from age 8 and 11. They found excess weight resulted in an increase in the rate of not only asthma and wheezing but also sleep-related disorders (Amer Jour of Resp and Crit Care Med 2005;171:659-664). “Compared with those with neither wheeze nor asthma, children with active wheeze had significantly higher BMI and a greater prevalence of obesity,” says Dr. Sulit. At any age, the combination of asthma and obesity also seems to result in more serious asthma attacks. Obese or overweight individuals constitute 75% of people seeking emergency room asthma treatment (Chest 2003;124:795-802). “The incidence of asthma and obesity is increasing worldwide, and asthma is often more severe in the obese,” says Christie Ballantyne, MD, director of the Center for Cardiovascular Disease Prevention at the Methodist DeBakey Heart Center in Houston. “We found that fat tissue inside of the abdomen is an important source of eotaxin, a molecule that is an inflammatory mediator known to play a key role in asthma.” Inflammation is a central feature of asthma. The inflammatory process leads to increased mucus production and sensitivity in the airways of the lungs. Once inflammation is present, the bronchial tubes become sensitive to conditions or environmental factors in the environment. These things act to trigger a constriction or tightening of the airways, causing the classic asthma symptoms of wheezing, chest tightness, and shortness of breath. This is why anti-inflammatory medications such as inhaled corticosteroids are a major part of care plans for those diagnosed with moderate to severe asthma. Research into the role of inflammation in the disease process is gaining momentum. One current area of interest is how fat tissue plays a role in creating hormones such as leptin that cause low-grade inflammation throughout the body. The clinically obese are known to have higher-than-average leptin levels. Regardless of weight, asthmatics have increased blood levels of leptin, which suggests it plays a role in the disease. In addition, fat tissue also appears to decrease the blood levels of adiponectin, a hormone that has anti-inflammatory properties (Cur Opin Pharma 2004;4:281-289).
Losing Weight Can Be an Effective Asthma Treatment The good news is that losing weight helps the clinically obese breathe more easily. In a randomized controlled study from Finland, 38 people with a BMI of at least 30 treated for moderate asthma with corticosteroids were placed on a strict, supervised diet (Br Med J
Calculating Your BMI he Centers for Disease Control and many physi-
T
cians use the body mass index (BMI) to measure
whether adults are overweight or obese because it is easy to use. (For children and adolescents, the calculation is more complex.) The use of BMI allows people to compare their own weight status to that of
2000;320:827-832). The average weight loss in the group was about 40 pounds. “Their lung function improved, there was less obstruction of the airways, and they also found that their quality of life was much better,” says Dr. Brita Stenius-Aarniala, professor of Pulmonary Medicine and Allergy at Helsinki University Central Hospital, Helsinki, Finland. “They used less asthma medication, and the group who lost weight, when we followed them for a year, had fewer admissions to hospitals than the group that did not lose weight.” She admits she is not sure why weight loss can lead to such a marked improvement in asthma symptoms. She speculates symptoms may improve because less weight eases the mechanical load on breathing and less fat on the chest wall reduces compression of the bronchial tubes. In small studies, people who have lost considerable amounts of weight after undergoing bariatric surgery report that their asthma symptoms improved or disappeared. Dr. Ford of the CDC says there is a need for large, randomized clinical trials on weight loss, including bariatric studies, to yield valuable insights into the obesity-asthma relationship. “Whether weight-loss programs need to be tailored to patients with asthma deserves consideration,” Dr. Ford
the general population. The only information required to calculate an adult’s BMI are height and weight. For more information, and to calculate your BMI, go to www.cdc.gov/nccdphp/dnpa/bmi/calc-bmi.htm.
says. A program of calorie restriction and increased exercise produces the most consistent long-term weight loss. By losing weight this way, asthmatics can increase their level of physical activity and improve their overall health. “Health care professionals can help to dispel any lingering doubts among most asthmatic patients about their ability to engage in adequate physical activity,” Dr. Ford says. “Clearly, many aspects of obesity and asthma deserve further research.” Gregory Alford is a freelance writer and health columnist for several newspapers in Illinois. Reprint orders: Elsevier, Inc., 11830 Westline Industrial Dr. St. Louis, MO 63146-3318; phone 314-453-4350. doi:10.1016/j.asthmamag.2005.07.001
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