Children in urban areas with high pollution ‘at higher risk of obesity’

Children raised in urban areas with high levels of air pollution, noise and traffic may be more susceptible to childhood obesity, according to researchers in Spain.

A study of more than 2,000 children by explored how these three crucial environmental factors could have an impact on children’s weight.

The Barcelona Institute for Global Health (ISGlobal) and the University Institute for Primary Care Research Jordi Gol examined youngsters aged from nine to 12 in the nearby city of Sabadell.

It was found that around 40 per cent of children were overweight or clinically obese at the time of the study, with traffic, noise and pollution all factors in the youngsters’ conditions. The development of community-led health provisions to promote healthy behaviours, say researchers, can best be tackled by fundamentally understanding the mechanism of the relationship between an urban environment and childhood obesity.

‘Three crucial environmental factors’

Their subsequent report, published in the Environment International professional journal, does not provide a definitive answer as to what causes the link, but suggests that a key element may be air pollution inducing inflammation or stress, hormone disruption and fat which sits in the abdomen and wraps around your organs, known as ‘visceral adiposity’.

The researchers investigated the association between urban factors that the children were exposed to between October 2017 and January 2019 (ambient air pollution, green spaces, built environment, density of unhealthy food establishments, road traffic and road traffic noise) and various measures of childhood obesity (body mass index, waist circumference and body fat) and weight-related behaviours (fast food and sugar-sweetened beverage consumption, physical activity, sedentary behaviour, sleep duration and well-being).

To date, few studies have assessed whether the urban environment influences children’s behaviours in order to better understand the relationship between this environment and the risk of childhood obesity. An understanding of the mechanisms of this relationship will facilitate the development of community-level health promotion programmes to encourage healthier behaviours in the city. Another novel aspect of this study is that it assessed multiple urban exposures together, in accordance with the concept of exposome – the measure of all the exposures of an individual in a lifetime and how those exposures relate to health – or the study of multiple simultaneous environmental factors.

Possible mechanisms

Jeroen de Bont, part of the research team, said: “Higher levels of air pollution, traffic and noise were associated with higher body mass index and a higher likelihood of the child being overweight or obese.”

Although the mechanisms that could explain this association remain unknown, the scientific team proposed various hypotheses. Air pollution could disrupt the molecular mechanisms that cause obesity by inducing inflammation or oxidative stress, hormone disruption and visceral adiposity (although the studies published to date have been performed in mice). Noise could influence sleep deprivation and increase stress hormones, which are associated with physical development in childhood and could increase the risk of becoming overweight.

The findings were consistent with those obtained in the same study when some environmental exposures were analysed separately. In particular, the number of unhealthy food establishments in an area was also found to be associated with childhood obesity, probably because such an environment may favour higher fast food consumption and higher caloric intake.

The study did not, however, find an association between the urban environment and the level of physical activity, sedentary behaviour and other weight-related behaviours in children, although it is thought that such factors could play a role. (For example, in areas with a good public transport network and nearby facilities and shops, journeys tend to be made on foot or by bicycle, which increases children’s physical activity.)

‘Socioeconomic status played an important role’

The fact that the study did not find an association between these factors could be attributed, added de Bont, to ‘the difficulty of determining to what extent obesity itself influences weight-related behaviours’. In addition, information on children’s physical activity was collected using a questionnaire that did not take into account where the activities took place.

“We were able to find out if the children played basketball or football, but not if they cycled in nearby green spaces, for example,” he added.

Finally, socioeconomic status was also found to play an important role in the association between the urban environment and childhood obesity that is not yet clear, according to fellow author Martine Vrijheid, also researcher at ISGlobal.

In this study, funded by the La Marató de TV3 Foundation, children living in more deprived areas on the outskirts of the city had higher rates of overweight and obesity even though they were exposed to lower levels of air pollution, road traffic and noise and had access to more green spaces.