A study run through BBC Radio 4’s “All in the Mind” programme, found that traumatic life events were the single biggest determinant of anxiety and depression.
Other factors included a family history of mental illness along with income and education levels.
Relationship status and social factors were also significant but smaller contributors to stress.
The study also found that a person’s thinking style had just as much impact as the events that triggered the emotional reaction.
Participants completed a range of questions about their family history of mental health problems, live events, income and education, relationship and social circumstances.
They were also asked questions about how they responded to stressful situations, for example did they talk to friends, turn to alcohol or blame themselves.
More than 32,000 people aged 18-85 years took part making it the biggest such study in the UK.
The results were analysed by the University of Liverpool’s Institute of Psychology, Health and Society.
Professor Peter Kinderman, Head of the Institute who lead the research, said: “Depression and anxiety are not simple conditions and there is no single cause. We wanted to find out more about what caused people to suffer from anxiety and depression and why some people suffered more than others.
“Whilst we know that a person’s genetics and life circumstances contribute to mental health problems, the results showed that traumatic life events are the main reason people suffer from anxiety and depression.
“However, the way a person thinks about, and deals with, stressful events is as much an indicator of the level of stress and anxiety they feel.”
“We can’t change a person’s family history or their life experiences, it is possible to help a person to change the way they think and to teach them positive coping strategies that can mitigate and reduce stress levels.”
Mental health problems affect one person in every four, making it the leading cause of disability.
The research is published in PLOS One.