Children who are obese are much more likely to suffer with depression and anxiety. They also have a much higher risk of dying prematurely in early adulthood, two new studies suggest.

The World Health Organization (WHO) classes childhood obesity as one of the most serious public health challenges of the 21st century.

Previous studies have linked this issue with an increased risk of premature death from middle adulthood. Researchers in Sweden set out to find if children with obesity also had a higher risk of premature death in early adulthood.

They also wanted to investigate whether these children were more likely to suffer with depression and anxiety compared to children who were not obese.

For the premature mortality study, the researchers looked at around 7,000 people who had received treatment for obesity at some point between the ages of three and 17 years. These were compared to a control group of around 34,000 people.

While the overall number of people who died was relatively low, the researchers found that those who were obese as children were three times more likely to die prematurely in early adulthood compared to the control group.

The average age at the time of death was just 22 years.

"Our study shows that children with obesity have a significantly higher risk of premature mortality already as young adults. Both the risk of death from somatic diseases, of which more than a quarter were directly related to obesity, and the risk of suicide were increased for this group.

"We did not, however, see an increased risk of mortality from injuries or external causes such as criminal acts," explained one of the study's authors, Emilia Hagman, of the Karolinska Institute.

The researchers said that possible explanations for these findings may be that childhood obesity has been linked to somatic diseases such as diabetes, liver disease and high blood pressure. Young people with obesity are also more exposed to discrimination, which could lead to psychological problems.

Meanwhile, another study by the same group found that girls with obesity had a 43% increased risk of suffering with depression and anxiety compared to girls in the general population, while obese boys had a 33% increased risk.

That study looked at over 12,000 children between the ages of six and 17 years who had been treated for obesity during childhood. They were compared to a control group of 60,000 children.

These findings stood even after other risk factors were taken into account, such as family history of mental health problems and socioeconomic status.

"Taken together, our studies highlight the vulnerable situation that children with obesity are in. Anxiety and depression cause emotional and physiological stress and suffering, and may also hinder obesity treatment.

"It is important that children with obesity are offered adequate and long-term treatment early in life to reduce these risks," the researchers said.

Details of these findings are published in two journals, PLOS Medicine and BMC Medicine.