The ML models helped identify changes in the tone and content of language that people used as the first wave of the Covid-19 pandemic progressed.

The team from Massachusetts Institute of Technology (MIT) and Harvard University showed they can track the pandemic's impact on mental health by analysing the language that people use to express their anxiety online.

"We found that there were these natural clusters that emerged related to suicidality and loneliness, and the amount of posts in these clusters more than doubled during the pandemic as compared to the same months of the preceding year, which is a grave concern," said Daniel Low from Harvard and MIT and the lead author of the study.

The analysis revealed varying impacts on people who already suffer from different types of mental illness.

"When the mental health needs of so many in our society are inadequately met, even at baseline, we wanted to bring attention to the ways that many people are suffering during this time, in order to amplify and inform the allocation of resources to support them," says Laurie Rumker, a graduate student in the Bioinformatics and Integrative Genomics PhD Program at Harvard and one of the authors of the study.

Satrajit Ghosh, a principal research scientist at MIT's McGovern Institute for Brain Research, is the senior author of the study published in the Journal of Internet Medical Research.

The researchers analysed posts from 15 sub-reddit groups devoted to a variety of mental illnesses, including schizophrenia, depression and bipolar disorder.

Using several types of natural language processing algorithms, the researchers measured the frequency of words associated with topics such as anxiety, death, isolation, and substance abuse, and grouped posts together based on similarities in the language used.

The researchers found that while people in most of the support groups began posting about Covid-19 in March, the group devoted to health anxiety started much earlier in January.

They also discovered that the mental health groups affected the most negatively early in the pandemic were those related to ADHD and eating disorders.

The researchers also found the introduction of new topics specifically seeking mental health help or social interaction.

"The topics within these subreddit support groups were shifting a bit, as people were trying to adapt to a new life and focus on how they can go about getting more help if needed," said Talkar.

The researchers now plan to apply this approach to study whether posts on Reddit and other social media sites can be used to detect mental health disorders.

The findings could help psychiatrists, or potentially moderators of the Reddit forums that were studied, to better identify and help people whose mental health is suffering, the researchers said.