Gay, lesbian, bisexual and "questioning" children as young as 10 are more likely to suffer depressive symptoms and self-harm with suicidal intent, a study has revealed.
Researchers found that depressive symptoms increase at a higher rate through adolescence among LGBQ youngsters than for their heterosexual peers.
The study, led by University College London and published in The Lancet Child and Adolescent Health journal, said LGBQ young people were also more likely to have self-harmed recently.
It added that LGBQ young people were four times more likely to self-harm with suicidal intent than heterosexuals.
Senior author Dr Gemma Lewis said it was "concerning" to see that the decline in mental health started when children were as young as 10.
The study is the first of its kind in the UK and included 4,828 young people from the Children Of The 90s birth cohort, the Avon Longitudinal Study of Parents and Children (Alspac), who had reported their sexual orientation at age 16.
The team grouped all participants who were not exclusively heterosexual into the same "sexual minority" category, including 625 people who described themselves as homosexual, bisexual, mainly homosexual, mainly heterosexual, unsure or not attracted to either sex.
Participants responded to questions about depressive symptoms seven times from the age of 10 to 21, and at 16 and 21 were asked if they had attempted to hurt themselves in the past year.
The study only asked the children and young people about their sexual orientation, not their gender identity and the acronym LGBT is not used because transgender and non-binary identities were not among the variables.
The study found depressive symptoms increased throughout adolescence in both groups but the increase was greater for sexual minority youth. It said sexual minority young people were more likely to report depressive symptoms from age 10 and self-harm was more common among non-heterosexuals at ages 16 and 21.
At age 18, LGBQ adolescents were twice as likely to fulfil the criteria for a clinical diagnosis of depression, researchers found.
Mental health outcomes were worse for each of the sexual minority groups compared with heterosexuals.
The study did not investigate the reasons behind these differences but said discrimination, isolation, shame and fear of rejection could all be factors. First author Madeleine Irish, of King's College London, said it is thought that the child's sense of feeling different might affect their mental health before they can say what that difference is.