The legalisation of same-sex has caused suicide rates among gay men and lesbians in Sweden and Denmark to drop significantly. (ROBYN BECK/AFP via Getty)

The numbers of lesbians and gay men dying by suicide in Sweden and Denmark has reduced by almost half since the legalisation of same-sex marriage, a study has shown.

Denmark was the first country in the world to allow civil unions for same-sex couples in 1989, and Sweden in the same in 1995. The UK did not legalise them until 2004.

Same-sex marriage was legalised in Sweden in 2009, and in Denmark in 2012.

The joint study by the Danish Research Institute for Suicide Prevention and researchers from Stockholm University used data from national population registers in Denmark and Sweden.

Comparing two periods 13-year periods, 1989 to 2002 and 2003 to 2016, they looked at deaths by suicide of people in same-sex couples during the time both countries legalised civil partnerships and the time they both legalised same-sex marriage.

Suicides among those in same-sex partnerships fell by 46 percent between the two periods.

This is partly due to improved understanding of mental health, as suicide rates also fell by 28 percent among heterosexual couples, but researchers believe reduced stigma influenced by same-sex marriage contributed to the huge drop.

Annette Erlangsen of the Danish Research Institute for Suicide Prevention told Reuters: “Being married is protective against suicide. Legalising same-sex marriage and other supportive legislative measures – they might actually reduce stigma around sexual minorities.”

The study states: “With the passage of time, legalisation of same-sex marriage and the expansion of rights and protections to same-sex couples, those minorities have become much more accepted in the Nordic countries and elsewhere.

“This might have decreased the stigmatisation, psychological stress and level of distress experienced by sexual minority people, thereby reducing their suicide risk.”

However the study also found that even in two of the most progressive countries in the world for LGBT+ rights, between 2003 and 2013 people in same-sex unions were still more than twice as likely to take their own lives than their straight counterparts.

The report said: “This points to the critical need for better understanding of suicide risk and protective factors in sexual minority populations.”