Babies living near busy streets are more likely to get fat when they are older, according to a study.
Nitrogen dioxide pollution generated by diesel engines such as trucks, vans and buses could disrupt children's fat burning, scientists say.
One study found that 10-year-olds who lived in polluted areas when they were babies were on average 2.2 kg (1 kg) heavier than those who grew up with clean air.
Experts say the first year in a baby's life is a "critical window", and parents should think carefully about where to raise their children and how it affects their health.
The research came after the World Health Organization found that 90 percent of the world's children breathe insecure air.
Children who spend the first year of their lives in areas of high levels of nitrogen dioxide pollution from vehicle emissions are probably one kilogram heavier than their peers at the age of 10, according to Southern California researchers
Researchers at the University of Southern California followed 2,318 children in the Golden State to track how environmental pollution impacted their body weight later in life.
They found that those who spent their first year of life in a polluted area gained weight faster as they got older.
In the study, she wrote: "Our study suggests that early life is critical [air pollution] can lead to an increased risk of a higher childhood [weight] Trajectories, which in turn can lead to obesity in children. "
Although the study has not pinpointed the reasons for this, it could be due to inflammation affecting the brain, the Guardian reported.
ILLEGAL CONTAMINATION LEVEL IN MORE UK MONITORING ZONES
Air pollution in the United Kingdom was described as "national embarrassment" in September.
The figures for 2017 showed that 37 out of 43 air quality zones in the UK had an illegal nitrogen dioxide load, the same number as in the previous year.
The average pollutant concentrations from exhaust gases fell in most places, according to the figures of the state and environmental charity ClientEarth.
In Greater London, however, the level is still more than double the legal limit, and even in areas such as South Wales, West Midlands, Glasgow and Greater Manchester, the limit is well exceeded.
Brighton, Worthing and Littlehampton in West Sussex – an area that was declared legal last year – crawled back just below the threshold, according to statistics.
The United Kingdom has exceeded the EU nitrogen dioxide pollution limits, in large part for diesel vehicles, since the 2010 regulations entered into force.
Air pollution causes an estimated 40,000 premature deaths per year in the UK and is associated with health problems ranging from childhood illnesses to heart disease and even dementia.
Jennifer Kim, a graduate student researcher, told the newspaper, "The most common thought is an inflammation of body systems like the lungs, which can affect the entire body – the brain that regulates the appetite and changes in lipid metabolism."
The research focused on the effect of nitrogen dioxide (NO2), which is illegal in most UK cities and urban areas around the world.
People are increasingly concerned about the effects of pollution as scientific studies do the damage they do to people's physical and mental health.
Other recent research has shown that vehicle air pollution increases the risk of low birth weight, birth defects and cot death.
A study published in October indicated that around 33 million visits by people with asthma in the world were caused by air pollution.
"We urge parents to be aware of where their little children are spending their time, especially considering these areas are near main roads," said Ms. Kim.
"The first year of life is a time of rapid development of various systems in the body [and] can prepare the future development of the institution. "
The research was published in the journal Environmental Health.
Professor Jonathan Grigg of Queen Mary University was not involved in the research, however, The Guardian said: "This study shows a link between increased body mass in children and the burden of road pollution from type 2 diabetes and diabetes Air pollution in adults.
"However, further research is needed to explain how toxins inhaled into the lungs affect the fat cells throughout the body."