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 curiosi-ty. The Centers for Disease Control and Prevention(CDC) and many physicians define clinical obesity ashaving a body mass index (BMI) of 30 or higher (see

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Researchers Find Obesity IsAssociated With Asthma

A Weighty Issue forThose With Asthma

By Gregory Alford

sidebar.) According to the CDC, 63.1 millionAmericans over the age of 20 are clinically obese. Anadditional 71.7 million are clinically overweight,which is a BMI rating of 25 to 29.

“Assuming a prevalence of obesity of 30% amongU.S. adults and estimates of relative risk ranging from1.6 to 3.0, [this] suggests that about 15% to 38% ofasthma in adults might be caused by obesity and thusmight be preventable,” says Earl Ford, MD, of theCenters of Disease Control and Prevention (CDC) inAtlanta.

Children and adolescents are not faring any better inthe battle of the bulge. The CDC reports the number ofoverweight children, ages 6 to 11 years old, increased376% between 1965 and 2002. During the same years,the number of overweight adolescents age 12 to 19 yearsold increased by 350%.

Also during this period, dramatic increases haveoccurred in the rate of asthma in the United States. TheCDC reports that 20.3 million people in the US cur-rently report having asthma, 9 million of them children.The number of people who report having asthmaincreased 75% from 1980 to 1994.

Current Research TrendsIn years past, the assumption was that many asthmat-

ics were obese because their physical limitations causedor contributed to their weight gain. However, recentstudies suggest chemical changes in the body caused byobesity may be contributing to the increase in the inci-dence of asthma. Current areas of investigation include:

• Increased physical stress caused by excess weightmay reduce lung capacity (J Appl Physiol1995;79:1199-1205).

• The obese take additional, shallower breaths thanpeople of normal weight. This increases airwayresponsiveness to allergens and other asthma trig-gers, and narrows the airways (J Appl Physiol1983;55:1269-1276).

• Carrying too much body weight causes an increasein the production of certain compounds that resultin low-grade inflammation, which increases the riskof asthma, type 2 diabetes and cardiovascular dis-ease (J Allergy and Clin Immun 2005;115:925-7).

Although researchers are making headway, they stillhave more questions than answers about the linkbetween obesity and asthma. “Obesity has the capacityto impact lung function in a variety of ways,” saysJeffrey Fredberg, professor of bioengineering and physi-ology at Harvard University in Cambridge,Massachusetts. “None of them are good and all of themare poorly understood. More research is needed toexplain the relationship between asthma and obesity.”

Obesity’s Role in Asthma: What theResearch Shows

A plethora of studies show clinically obese childrenare more likely to be asthmatic than children of average

weight. In one study, Loreto G. Sulit, MD, of RainbowBabies and Children’s Hospital at Case UniversitySchool of Medicine in Cleveland, led a research teamthat studied medical records of 788 children from age 8and 11. They found excess weight resulted in an increasein the rate of not only asthma and wheezing but alsosleep-related disorders (Amer Jour of Resp and Crit CareMed 2005;171:659-664).

“Compared with those with neither wheeze nor asth-ma, children with active wheeze had significantly higherBMI and a greater prevalence of obesity,” says Dr. Sulit.

At any age, the combination of asthma and obesityalso seems to result in more serious asthma attacks.Obese or overweight individuals constitute 75% of peo-ple seeking emergency room asthma treatment (Chest2003;124:795-802).

“The incidence of asthma and obesity is increasingworldwide, and asthma is often more severe in theobese,” says Christie Ballantyne, MD, director of theCenter for Cardiovascular Disease Prevention at theMethodist DeBakey Heart Center in Houston. “Wefound that fat tissue inside of the abdomen is an impor-tant source of eotaxin, a molecule that is an inflammato-ry mediator known to play a key role in asthma.”

Inflammation is a central feature of asthma. Theinflammatory process leads to increased mucus produc-tion and sensitivity in the airways of the lungs. Onceinflammation is present, the bronchial tubes becomesensitive to conditions or environmental factors in theenvironment. These things act to trigger a constrictionor tightening of the airways, causing the classic asthmasymptoms of wheezing, chest tightness, and shortness ofbreath. This is why anti-inflammatory medications suchas inhaled corticosteroids are a major part of care plansfor those diagnosed with moderate to severe asthma.

Research into the role of inflammation in the diseaseprocess is gaining momentum. One current area ofinterest is how fat tissue plays a role in creating hor-mones such as leptin that cause low-grade inflammationthroughout the body. The clinically obese are known tohave higher-than-average leptin levels. Regardless ofweight, 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 ofadiponectin, a hormone that has anti-inflammatoryproperties (Cur Opin Pharma 2004;4:281-289).

Losing Weight Can Be an EffectiveAsthma Treatment

The good news is that losing weight helps the clini-cally obese breathe more easily. In a randomized con-trolled study from Finland, 38 people with a BMI of atleast 30 treated for moderate asthma with corticosteroidswere placed on a strict, supervised diet (Br Med J

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2000;320:827-832). The average weight loss in thegroup was about 40 pounds.

“Their lung function improved, there was lessobstruction of the airways, and they also found thattheir quality of life was much better,” says Dr. BritaStenius-Aarniala, professor of Pulmonary Medicine andAllergy at Helsinki University Central Hospital,Helsinki, Finland. “They used less asthma medication,and the group who lost weight, when we followed themfor a year, had fewer admissions to hospitals than thegroup that did not lose weight.”

She admits she is not sure why weight loss can lead tosuch a marked improvement in asthma symptoms. Shespeculates symptoms may improve because less weighteases the mechanical load on breathing and less fat on thechest wall reduces compression of the bronchial tubes.

In small studies, people who have lost considerableamounts of weight after undergoing bariatric surgeryreport that their asthma symptoms improved or disap-peared. Dr. Ford of the CDC says there is a need forlarge, randomized clinical trials on weight loss, includ-ing bariatric studies, to yield valuable insights into theobesity-asthma relationship.

“Whether weight-loss programs need to be tailored topatients with asthma deserves consideration,” Dr. Ford

says. A program of calorie restriction and increased exer-cise produces the most consistent long-term weight loss.By losing weight this way, asthmatics can increase theirlevel of physical activity and improve their overall health.

“Health care professionals can help to dispel any lin-gering doubts among most asthmatic patients abouttheir ability to engage in adequate physical activity,” Dr.Ford says. “Clearly, many aspects of obesity and asthmadeserve further research.”

Gregory Alford is a freelance writer and health columnistfor 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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Calculating Your BMI

The Centers for Disease Control and many physi-

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

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.