The study found bisexual women were less likely to be 'out' to friends, family and work colleagues and also less likely to be in a relationship. According to the results, bisexual women were less likely to experience sexuality-related discrimination from work, health care services, education and family than lesbians, but more likely to experience discrimination from friends.
Bisexual women were 64% more likely to report an eating problem and 37% more likely to have deliberately self-harmed than lesbians. They were also 26% more likely to have felt depressed and 20% more likely to have suffered from anxiety in the previous year than lesbians.
Study senior author Dr Ford Hickson, at the London School of Hygiene & Tropical Medicine, said, "Bisexual people are at particular risk of invisibility and marginalization from both gay/lesbian communities and mainstream society. Although bisexual women in our study reported experiencing less sexuality-based discrimination than lesbians, this did not benefit their mental health. Mental health services should be aware of both the differences and the similarities in bisexual and lesbian women's mental health care needs, and tailor the services they provide accordingly."
The authors also found that older bisexual women had more suicidal thoughts than younger bisexual women. Additionally, bisexual women were more likely to report poor physical health and more likely to use marijuana or tranquilizers than lesbians.
Study lead author Lisa Colledge, who conducted the research at the London School of Hygiene & Tropical Medicine, added, "These disturbing results echo international findings on mental health differences between bisexual and homosexual people. Although non-heterosexual women as a group have far poorer mental health than heterosexual women, bisexual women report even worse mental distress than lesbians. All women deserve equal chances of mental wellbeing and happiness, regardless of their sexuality. Homophobic prejudice is now widely and rightly condemned; specific stigma around bisexual identity needs to be similarly confronted."
In the UK, the numbers of women identifying as lesbian and as bisexual are similar. However, only 16% of the survey participants were bisexual women. The study authors suggest this may be linked to bisexual women's reluctance to disclose their sexual identity. The authors add that "concealment of sexual orientation is known to be related to poorer mental health in sexual minority women".
The study authors suggest that worse mental health in bisexual women than in lesbians may be due to more negative social attitudes towards bisexuality compared with lesbian and gay identity. Consequently, bisexual women may have a more negative attitude towards themselves, and expect more social rejection, putting their mental health at risk.
The new findings differ from those of a similar UK survey in 2003, which found no difference in psychological distress between bisexual women and lesbians. The authors suggest that legal and social changes in subsequent years (e.g. the 2004 Civil Partnership Act, and improvements in public attitudes towards lesbian and gay people) may have benefited lesbian women more than bisexual women. The 2012 Bisexuality Report highlights ongoing prejudice against UK bisexual people.
The authors note their findings may be limited because survey participants were not a random sample of the population and were therefore unlikely to be representative of all UK bisexual women and lesbians. They add that their findings are observed associations and it is therefore not possible to state that bisexual identity causes poorer mental health than lesbian identity.
Citation: Lisa Colledge, Ford Hickson, David Reid, Peter Weatherburn. Poorer mental health in UK bisexual women than lesbians: evidence from the UK 2007 Stonewall Women's Health Survey. Journal of Public Health. DOI:10.1093/pubmed/fdu105
 Eating problems (ever) were reported by 285 of 934 bisexual-identified women and 914 of 4750 lesbian-identified women; deliberate self-harm (in the last year) was reported by 274 of 932 bisexual-identified women and 862 of 4734 lesbian-identified women; the final, reported odds ratios for both outcomes were adjusted to account for identified confounders.
 Depressed feelings (in the last year) were reported by 785 of 933 bisexual-identified women and 3726 of 4756 lesbian-identified women; anxious feelings (in the last year) were reported by 727 of 929 bisexual-identified women and 3433 of 4738 lesbian-identified women; the final, reported odds ratios for both outcomes were adjusted to account for identified confounders.
 The 2007 Adult Psychiatric Morbidity Study (a representative sample survey of 7400 England private household residents) reported that 0.5% of women identified as bisexual and 0.3% as 'mostly or entirely' lesbian (Hayes J, Chakraborty AT, McManus S, et al. Prevalence of same-sex behavior and orientation in England: results from a national survey. Arch Sex Behav 2012;41(3):631-9), while the 2012 Integrated Household Survey (a representative sample survey of 340,000 UK respondents) reported that 0.5% of women identified as bisexual and 0.7% as lesbian (http://www.ons.gov.uk/ons/dcp171778_280451.pdf).
 Mental health and social wellbeing of gay men, lesbians and bisexuals in England and Wales (2003): http://www.mindout.org.uk/wp-content/uploads/2012/06/SummaryfindingsofLGBreport.pdf
 The Bisexuality Report: Bisexual Inclusion in LGBT Equality and Diversity (2012): http://www.open.ac.uk/ccig/files/ccig/The%20BisexualityReport%20Feb.2012.pdf