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Thursday, March 23, 2017

Body fat mass distribution and interrupter resistance, fractional exhaled nitric oxide, and asthma at school-age

Obesity and asthma are two of the most common childhood chronic diseases, seen in 25% and 10% of children, respectively.  There are increasing lines of evidence suggesting that they may be inter-dependent : fat may be the source of proinflammatory mediators and may change the mechanics of lung function. 

However, not all fat is considered equal.  The android distribution of fat along the abdomen, compared to gynoid distribution along the hips, is more closely associated with a variety of cardiometabolic diseases.  Similarly, visceral fat, situated just above the guts in the belly, is considered a marker of inflammatory status, compared to more superficial subcutaneous fat deposits.  In this month’s issue of JACI, den Dekker and colleagues discuss the effect of body fat mass distribution on asthma and airway function in children (J Allergy Clin Immunol 2017; 139(3): 810-816).

To do this, they looked at the medical histories and physical characteristics of 6178 children.  They focused on body-mass index (BMI), total and abdominal fat measures using ultrasonography and dual energy x-ray absorptiometry (DEXA), respiratory resistance (Rint), fractional exhaled nitric oxide (FENO), wheezing, and asthma.   They found that a higher BMI was associated with increased respiratory resistance and current wheezing.  They also noted that more visceral fat was associated with a higher FENO, while a higher android (belly)/gynoid (hip) ratio was associated with a lower FENO. 

Altogether, these results suggest that local fat deposition, especially visceral fat, is more closely related to asthma.  Even though the reasons for this are unclear, the authors speculate that maybe the different metabolic profiles of visceral vs. subcutaneous fat and the mechanical effects may be responsible for these differences.  Regardless, understanding the finer details of fat composition and distribution may help to explain part of the increased prevalence of childhood asthma.

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