Denmark implemented the world's first national law on registered same-sex partnerships in 1989. Mortality was markedly elevated among people in same-sex marriages for the first several years after this, but since 1996, with the advent of effective treatment of HIV/AIDS, mortality among men married to men has dropped to a level below that of unmarried or divorced men.

In contrast, the study also found that women married to women were at increased risk of mortality, most notably from suicide and cancer. In response to this, Morten Frisch, lead author of the study, says, "Lesbians may constitute a largely unnoticed high-risk population for suicide and breast cancer, so our findings call for efforts to identify the underlying factors responsible and ensure access to basic health care in this population."

Morten Frisch (Statens Serum Institut, Copenhagen, and Aalborg University, Aalborg) and statistician Jacob Simonsen (Statens Serum Institut, Copenhagen) used Denmark's Civil Registration System to follow 6.5 million adults who resided in Denmark for any period between 1 January 1982 and 30 September 2011 for a total of 122.5 million person-years. No prior study has explored overall and cause-specific mortality in an entire country using complete day-by-day information about actual living arrangements over this time frame. Taking socioeconomic confounders available since 1982 into account, the authors were able to address how living arrangements were linked with overall and cause-specific mortality.

Marriage has long been known to be associated with reduced mortality, but noticeable changes have occurred in the marital status distribution of Western populations over the past decades. Gradual declines have been seen in proportions of people married to members of the opposite sex, and widowed people; with corresponding increases in proportions of unmarried and divorced people. The study also noted decreasing proportions of people cohabiting with a member of the opposite sex and corresponding increases in single people.

Being married or cohabiting with a member of the opposite sex was associated with consistently lower mortality than all other marital status or cohabitation categories. Interestingly, though, by combining data about marital and cohabitation status, the study revealed a two-fold or higher mortality in married persons not living with their spouse, a finding that has not been reported before.

Morten Frisch says, "It is a novel observation that being married was not always protective. Among persons living alone and persons living in same-sex cohabitation, those who were married to a member of the opposite sex had noticeably higher mortality than unmarried and same-sex married persons."

"From a public health viewpoint it is important to try to identify those underlying factors and mechanisms that explain the lower mortality among married and cohabiting persons."

Key Messages:

- Marriage has long been known to be associated with reduced mortality, but noticeable changes have occurred in the marital status distribution of Western populations over the past decades.

-- This study assessed changes in marital status and cohabitation status in Denmark over a 30-year period and their associations with mortality, using continuously updated individual-level information on living arrangements, confounders, and deaths.

-- Compared with people married to a member of the opposite sex, hazard ratios for overall mortality were consistently elevated in unmarried, divorced, widowed, or same-sex married people. Likewise, compared with people cohabiting with a member of the opposite sex cohabiting, hazard ratios for overall mortality were consistently elevated among people who lived alone, with parents, in multi-adult households, or in same-sex cohabitation.

-- The most marked changes in mortality were seen among same-sex married persons. Between 2000 and 2011, same-sex married Danish women emerged as a group with particularly increased mortality; in contrast, same-sex married Danish men now have mortality rates that are lower than those of unmarried or divorced men.

Note: If no author is given, the source is cited instead.

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