Increased abdominal fat associated with impaired lung function in adolescents
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Key takeaways:
- Subcutaneous and visceral fat mass indices were associated with lower FEV1, FEV1/FVC and FEF75.
- Boys experienced larger effect estimates for these associations than girls.
Adolescents with greater amounts of abdominal fat depots compared with their peers also had reduced lung function, regardless of previous adiposity or BMI, according to a study published in Pediatric Allergy and Immunology.
These findings suggest that interventions that reduce abdominal fat mass may improve respiratory health for these patients, Tong Wu, MD, PhD student, Generation R Study Group, Erasmus MC, University Medical Center, and colleagues wrote.
The cohort included 2,877 children (51.9% boys) from the population-based Generation R Study with information on specific abdominal fat deposits at ages 10 and 13 years. At birth, median gestational age was 40.1 weeks, and median weight was 3,437 g.
Also, 2,653 had information about lung function and 2,564 had information about current asthma, both at age 13 years, with 154 (6%) reporting current asthma.
More than half (53%) of the mothers of the children in the cohort had a “high” educational level, 77.6% did not smoke during pregnancy and 58.8% were nulliparous.
A confounder model indicated an association between lower FEV1, FEV1/forced vital capacity (FVC) ratio and forced expiratory flow after exhaling 75% of FVC (FEF75) and higher subcutaneous fat mass index at age 13 years.
Additional adjustments for BMI yielded consistent associations between lower FEV1 and subcutaneous (z score difference = –0.06; 95% CI, –0.11 to –0.01) and visceral (z score difference = –0.09; 95% CI, –0.14 to –0.04) fat mass index.
Consistent associations also were found between lower FEV1/FVC and subcutaneous (z score difference = –0.1; 95% CI, –0.15 to –0.05) and visceral (z score difference = –0.08; 95% CI, –0.13 to –0.04) fat mass index.
FEF75 had a consistent association with subcutaneous (z score difference = –0.1; 95% CI, –0.15 to –0.5) and visceral (z score difference = –0.1; 95% CI, –0.15 to –0.6) fat mass index as well.
For most of these associations, the researchers said, the size and direction of these effect estimates remained similar after adjustment for lung function or asthma at age 10 years.
Also, the researchers found associations between each unit increase in the change of subcutaneous and visceral fat mass indices and decreases in FEV1, FEV1/FVC and FEF75 between ages 10 and 13 years (range z score difference = –0.13; 95% CI, –0.18 to –0.08 to –0.06; 95% CI, –0.11 to –0.01) based on their main model and after accounting for lung functions at age 10 years.
However, the researchers said, they did not observe any associations of change in abdominal fat deposits with changes in asthma.
The researchers additionally said there were consistent interactions between subcutaneous fat mass index at age 13 years and sex in associations between FEV1 (P = .012) and FVC (P = .01) and asthma, but not with any other specific abdominal fat depot measures and sex, allergic sensitization or puberty status for associations with lung functions and asthma.
Boys had larger effect estimates for associations between subcutaneous and visceral fat mass index and lower FEV1 and FVC, both at age 13 years, than girls in stratified analyses.
The researchers also did not report any non-linearity for associations between abdominal fat measurements and respiratory outcomes among adolescents.
An exploratory examination of the extremes indicated large effect sizes as well, including some that were non-significant, for associations between very high subcutaneous fat index and higher risks for FEV1, FEV1/FVC and FEF75 under the lower limits of normal (range z score change = 1.62; 95% CI, 0.86-3.07 to 2.77; 95% CI, 1.37-5.6).
Associations were similar for high visceral fat mass index and higher risk for FEV1, FVC, FVC1/FVC ratio and FEF75 under the lower limit of normal (range z score change = 1.4; 95% CI, 0.74-2.65 to 2.33; 95% CI, 1.18-4.59).
Although the researchers concluded that there were associations between higher levels of visceral fat and obstructive lung patterns both at age 13 years, they did not see any associations between visceral fat at age 10 years and lung function at age 13 years.
However, they continued, the changes in fat indices between ages 10 and 13 years and their associations with changes in lung function may indicate that lung health may be impacted by changes in body composition around puberty.
The researchers also suggested that stronger associations between specific abdominal fat depot measures and FEV1 and FVC at age 13 years among boys compared with girls could be attributable to differences in fat distribution between the sexes in puberty.
The lack of associations between abdominal fat indices and asthma, the researchers continued, may indicate a more prominent effect on dysanaptic growth in the lungs from increases in abdominal fat deposits during puberty.
Further, the researchers said, these effects may decrease airway capacity and obstruct airflow without influencing how fat tissue produces pro-inflammatory cytokines, which would cause airway inflammation and asthma symptoms.
By reducing abdominal fat mass in specific compartments, the researchers said, adolescents may experience improved respiratory health, although further research into the causality and potential underlying mechanisms of these associations from childhood into adolescence and adulthood are necessary.
Perspective
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This study looked at lung function in adolescents aged 13 years in relation to subcutaneous (under the skin) fat mass and visceral (near organs) fat mass. The participants in the study underwent MRI to determine location and proportion of body fat.
Results of the study demonstrated that the adolescents with higher amounts of both types of fat mass had a significant decrease in markers of lung function that were separate from underlying asthma. These results are not surprising.
The act of breathing is a well-orchestrated process from signals in the brain that trigger the diaphragm, the muscle of respiration, to contract and expand into the abdomen. The muscles between the ribs engage and pull the rib cage upward and outward to allow the lungs space to expand.
The act of lung expansion can be limited in lung diseases that cause fibrosis, or stiffening of the lungs. Lung expansion is also significantly impacted when something outside the chest cavity prevents the diaphragm from expanding, such as pregnancy as the uterus enlarges, or carrying extra weight around the midsection.
The same phenomenon can be seen with decreased rib expansion when wearing clothing that is too tight or in having extra fat tissue in the area of the chest. Fat tissue itself produces inflammatory signals that can worsen underlying asthma, as these signals can cause increase in airway inflammation.
This study demonstrates how it is important to identify children at risk for having overweight or obesity before adolescence. Before adults are identified as having decreased lung function, they have already subconsciously decreased their physical activity because of shortness of breath for years. This leads to decreased aerobic activity and weight gain.
This same process in children could have lifelong detrimental effects for heart health, lung health and weight. Continued research is needed in this area in order to determine the best interventions to support a lifetime of breathing.
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