The mental health of Australians declined from 2010 but researchers are grappling to understand why.
Research authors from the University of Sydney, University of Melbourne and ANU said causes could be the rise of social media, climate change, poor sleep or an increased willingness to discuss mental health issues.
University of Sydney's Richard Morris said a number of things happened in the first decade of the millennium, particularly around 2010.
"The (Global Financial Crisis) occurred in 2008 and the austerity measures that occurred after that could have a big impact," Dr Morris said.
"There were changes to social media, so Facebook news feeds were updated, Twitter started offering retweets."
Dr Morris said new research on mental health commonly focuses on younger groups but this data shows that it's not just Australian youth that are feeling the sting.
"What's interesting about our results is that it's occurring in older cohorts like people born in the 1990s or even the 1980s," he said.
"Something happened either in the first decade of the millennium or somewhere on or before 2010 that produced these generational differences that we're starting to see.
"The timing of these generational differences seems to be an important clue."
Led by The University of Sydney, the research tracked Australian's over 20 years using The Household, Income and Labour Dynamics in Australia (HILDA) Survey.
The HILDA Survey follows the lives of 17,000 Australians each year and helped lead to the unsettling discovery affecting Australians well into their 40s and 50s.
Subjects involved in the research were asked to scale their recent happiness, as well as evaluate how they feel about things like their prospects, job security and finances.
It found that just because people are on track in life, it doesn't necessarily mean they're happy.
"You'd expect people that are doing well in life to also be happy, but the fact that they're not happy presents a problem," Dr Morris said.
The results show people with poor mental health may not necessarily improve.
In the past, research showed the mental health of much older Australians often improved with age but these new findings show people born from 1980 may never see similar improvements.
"The big implication is that where we might have previously had people spontaneously recover, this data is showing that this might not happen," Dr Morris said.
The next step for the researchers is to secure funding to work towards understanding what has most likely caused this decline in mental health for Australians.
"The prevailing hypothesis right now is that its probably social media or it's dissatisfaction with their economic situation," Dr Morris.
"Right now, we don't know. What we have done is identify a problem."
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