Church teaching on same-sex relationships contributes to negative attitudes in society, which in turn undermines the mental health of lesbian, gay and bisexual (LGB) people – leading to higher incidents of mental ill health, self-harm and suicide, a new report has said.

The report, ‘In the Name of Love: The Church, exclusion and LGB mental health issues’ by Christian charity the Oasis Foundation, contains what it calls “watertight” research that demonstrates that homosexual and bisexual people are up to 12 times more likely to experience mental health difficulties. It also presents what it believes is a continuingly growing consensus that this is caused by societal discrimination that says – explicitly and implicitly – that heterosexuality is superior to homosexuality. The study demonstrates “beyond reasonable doubt” that church goers and Christian leaders are responsible for fuelling negative messages about same-sex relationships in society, the media and political debate.

Previous studies have shown the damage done to LGB people within Christian denominations, but this is the first that seems to justify the long-held assumption that church practises and teachings are seriously damaging the mental health of LGB people outside the Church.

The research has been published in part to respond to the House of Bishops’ report, which restated the Church of England’s opposition to same-sex marriage and will be discussed at the General Synod meeting next week.

Previous research has indicated that non-heterosexual people are at increased risk of poor mental health, such as a study by the RAND Corporation, University of Cambridge, and Harvard Medical School in 2014.

Indeed, health bodies such as the NHS work on the basis that homosexual and bisexual people are more vulnerable to mental health issues.

But there is nothing intrinsic about being homosexual or bisexual that makes people susceptible to poor mental health, the report adds. Instead, through surveying a range of Western European studies, the report identified two major categories of causes:

• Direct homophobia and discrimination – whereby LGB people directly experience a lack of access to communities, bullying or inferior treatment because of their sexuality or membership of a same-sex relationship

• Societal inferiority – whereby LGB people feel second class because of explicit and implicit references in families, communities, the media and society that to be homosexual or bisexual is an inferior status to heterosexuality.

By analysing the practises of the major UK denominations, the study found that – with the exception of the United Reformed Church – all the church groups practise discrimination of LGB people in some form, making churches some of the biggest organisational discriminators.

It also found that churchgoers are the biggest source of negative attitudes toward same-sex relationships in the media, society and political debate. For instance, while only 37% of the general population opposed same-sex marriage in 2013, according to research by Oasis in 2015, opposition among churchgoers was 49%. Of the signatories listed on the website of the Coalition for Marriage (the campaign against same-sex marriage), 74% can be publicly identified as Christian.

In addition, an analysis of 100 national media articles on the topic of ‘same-sex marriage’ found that 47% contained a negative comment, of which 91% were from a Christian leader or commentator or politician who can be identified as Christian.

Reverend Steve Chalke, founder of Oasis, said: “It is no secret that the negative stance taken by the Church, and so many individual local churches, has a hugely distressing impact on large numbers of LGB people and leaves countless numbers of them living lives of forced secrecy and dishonesty. Tragically, it is also common knowledge that the resultant anguish and distress often leads to spiritual, mental and physical harm and in the worst of cases to people making the desperate decision to take their own life.

“Too often however, these powerful testimonies are dismissed by those that don’t want to hear them – those who are not yet ready to face up to the scale of the damage that we collectively have unintentionally caused. My hope is that this report is the beginning of a sea change to this approach.”