New research has drawn a concerning link between the ongoing disruption of COVID-19 lockdowns and worsening mental health for our most vulnerable.

An international study has drawn a link between that disruption and declining mental health for those with a mood disorder.

Nearly 40 percent of people included in the study reported moderate to severe depression during our first lockdown in 2020.

"Up until now, we've never had quite such a dramatic event that's changed large numbers of people's rhythms," researcher Richard Porter said.

Nearly 1000 people took part in the study from six different countries, with more than half the participants from New Zealand.

Half of the participants had been diagnosed with bipolar disorder and the other half had depression.

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The research showed that 12 percent of participants felt minimally depressed, 20 percent reported mild depression, 27 percent moderate depression, 21 percent moderate to severe and 18 percent severely depressed.

Porter said they weren't shocked by the results given the circumstances.

"Low moods, loss of energy, feeling generally sad - we weren't terribly surprised by that given what was going on at the time."

Study participants said some of the worst causes of COVID-19 disruption included not being able to go to work, forced home isolation and not being able to socialise as normal.

The study focussed on people who had mood disorders only, regardless, most people found lockdown challenging.

As long as COVID-19 is here, so is uncertainty and Porter said mental health needs more attention to detail.

"The most important thing is to try and keep the main things in your life as regular as possible."