Excessive calorie consumption and lack of excerise are the oft-cited drivers of childhood obesity in the US and abroad, but there may be more to the equation. Two recent studies shed light on previously unsuspected risk variables: overuse of antibiotics and exposure to air pollution.
Last year, Danish investigators published a landmark paper in the journal Nature, suggesting indicating that maternal exposure to antibiotics, as well as neonatal exposure to antibiotics during the first 6 months of life, could markedly increase the odds of obesity by age 7. The study was based on analysis of more than 28,000 mother-child diads in the Danish health care system's registries.
The connection is not entirely clear-cut, however. They found that antibiotic exposure in infancy increased the odds of overweight by 50% in children of normal-weight mothers, but decreased the risk in children of obese mothers.
Disrupted Gut Flora
Earlier this Spring, microbiologists at New York University, corroborated the observation that antibiotics can induce weight gain with a prospective animal experiement. They compared mice fed low daily doses of penicillin for 30 weeks with a cohort of similar animals not exposed, and found that those in the exposed group were 10-15% heavier, on average.
Interestingly, the mice in the antibiotic group showed signs of immune system suppression, namely significantly lower numbers of T-helper cells. The data were published in Nature Reviews-Microbiology.
How might antibiotics affect changes in weight? The Danish researchers point to changes in the gastrointestinal microbiome. Healthy commencal organisms in the gut play many diverse metabolic and neuroendocrine roles. Antibiotic exposure early in life disrupts the process of establishing a healthy and well-functioning gut microenvironment. Left uncorrected, the problem compounds over time, leading to metabolic dysregulation.
Foul Air, Fat Kids
Air quality, it turns out, can also influence childhood weight, and the process starts in utero.
Epidemiologists at Columbia's Mailman School of Public Health recently reported that chronic maternal exposure to high levels of airborne polycyclic aromatic hydrocarbons during pregnancy, more than doubled the odds that a child would be obese by age 7.
They base this assertion on a study of 702 non-smoking pregnant women recruited through prenatal clinics at two hospitals in Harlem. The women were ages 18-35, either African-American or Dominican, and lived in low income neighborhoods in Northern Manhattan or the South Bronx.
Ambient air quality and airborne toxin levels were assessed by having the women wear small small monitoring units that continuously sampled the surrounding air for two full days during the third trimesters of their pregancies. At night they placed the air monitors near their beds.
By age 5, 21% of the children in the cohort were obese, and this number increased to 25% by age 7. Exposure to airborne toxins turned out to be a robust predictor of the likelihood that a child would be obese.
After adjusting for a number of morphologic, demographic and socioeconomic variables they found a strong correlation between prenatal exposure to aromatic hydrocarbons and childhood body size. Children of mothers in the highest versus lowest tertiles of pollution exposure had a 0.30-unit higher BMI and a 2.26 relative risk of obesity by age 7. The data were published in the American Journal of Epidemiology.
Dr. Andrew Rundle, the lead author, believes that the correlation represents a very real phenomenon, one that cannot be explained away as an artifact or a reflection of other obesity-related variables. Many olycyclic aromatic hydrocarbon compounds, formed from incomplete combustion of carbon-based fuels including oil, deisel, and tobacco smoke, are know to be endocrine system disruptors. This, he suggested, could explain the connection between pollution exposure and changes in childhood metabolism.