A new Growing Up in Ireland report's found depression and obesity are major challenges for young people.
The research has been tracking the lives of young adults, who were 20 years old in 2018 and 2019.
They have been followed by the researchers since they were 9 years of age.
Almost one third of young Irish women and one in five young Irish men are experiencing symptoms linked to depression.
One of the reports co-authors, Dr Desmond O’Mahony, says mental health issues can begin when they are children.
"What we see is that if there have been episodes of high depressive in childhood you're much more likely to experience a depressive episode in your twenties."
The study also found nearly a quarter of young adults aged 20 are overweight and 13 percent obese.
Dr O'Mahony said the decline in physical activity post secondary school could be leading to the increase.
"That kind of structured physical activity you might have had in school falls away in your twenties".
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