The Body Mass Index (BMI) is a measure used to determine if a person is overweight or obese. It is calculated by dividing a person's weight I kilograms by the square of the height in meters. But for children and teens, it is age- and sex-specific and is often described as BMI-for-age.

According to the Centers for Disease Control and Prevention, obesity affects one in five children in the United States.

A new US study has classified air pollutants and population density as the factors that increase the risk of children becoming obese, The Guardian reports. Scientists are also beginning to understand which chemicals and urban factors contribute to their increased risk.

Factors Increasing the Risk of Childhood Obesity

The researchers reviewed 77 factors during pregnancy and 96 factors during childhood that might affect a child's likelihood of becoming obese. They found that air pollution, smoking, and a person's built environment may play a role in childhood obesity from birth to age 11.

But before this, the researchers have looked into single exposures individually though they have not analyzed the entire comprehensive characterization of the exposures or exposomes.

The lead author of the study, Martine Vrijheid, said that their research is one of the first studies that managed to measure so many different variables and factors of the environment and then tries to analyze all of them together.

"We thought it's also important to have this type of approach where you show all the results in one publication because it's the most systematic way of showing the data," the researchers said.

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Air Pollution and the Built Environment May Trigger Obesity

Among the children who participated in the study, 29% of them were either overweight or obese. According to Vrijhei, the figure might have increased due to the COVID-19 stay-at-home orders by the government.

Their study results suggest that air pollution was correlated with the highest obesity rates and BMI measurements. In one study of mice, air pollution is linked with internal inflammation, which decreased metabolism and led to weight gain.

Meanwhile, another study has shown that breathing polluted air during pregnancy is linked to lower birth weights, which led to the body trying to "catch up" after birth and speeds up weight gain, which induces obesity, said Vrijheid.

However, exposomes are not easy to evaluate. Environmental factors can be classified as harmful or beneficial, and it is challenging to know which ones outweigh the others.

For instance, air pollution is more rampant in urban areas but is more walkable than other habitats, increasing physical activity, and decreasing obesity, the study said.

Furthermore, another factor that could increase the risk of obesity the researchers found is the built environment in which the child grows. According to the research, this could also trigger obesity, especially on children living in a densely-populated area with fewer parks and less public transportation.

Children living under those conditions have higher BMIs because they have fewer chances of physical activity.

Moreover, the study also analyzed common toxic exposures, including PFAS chemicals, PCBs, and heavy metals. But it was still inconclusive because blood concentration could be affected by metabolic cycle and other factors.

The researchers recommend that it is essential to protect children from the damage of environmental pollutants as they are very susceptible to any possible effects from it.

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