Despite a global decline in suicide rates, the USA has witnessed a concerning rise in suicide mortality over the past two decades.

This study aims to elucidate the changing patterns of suicide mortality in the USA from 1999 to 2019, with a particular focus on gender and racial differences.

We utilised national mortality data for causes of suicide (X60–X84, Y87.0) from the Centers for Disease Control and Prevention for 1999–2019. The age–period–cohort analysis was conducted to explore the effects of age, period and birth cohort effects on suicide mortality by gender and race.

Between 1999 and 2019, the suicide rate and the number of suicides in the USA increased 33% and 62%, respectively. We discerned an emerging peak of suicide among young adult populations even as increases affected nearly all groups. Females have shown increasing period risk, which has exceeded that of males since 2011. Their cohort risk, which slowly increased and exceeded males in post-1959 cohorts, exhibited a steep J-shaped pattern, especially among those born after 1977. Although Americans of all races have experienced increased period risk since 2011, it was highest among American Indians and Alaska Natives by the end of the 20-year span. With the mortality risk increasing rapidly in all post-1959 cohorts, the risk showed an obvious cliff-shaped pattern among the Asian/Pacific Islander population born after 1989.

The shifting burden of suicide mortality towards younger populations, transcending gender and racial boundaries, underscores the need for the implementation of tailored public health strategies.

Despite the recognised importance of mental disorders and social disconnectedness for mortality, few studies have examined their co-occurrence.

To examine the interaction between mental disorders and three distinct aspects of social disconnectedness on mortality, while taking into account sex, age and characteristics of the mental disorder.

This cohort study included participants from the Danish National Health Survey in 2013 and 2017 who were followed until 2021. Survey data on social disconnectedness (loneliness, social isolation and low social support) were linked with register data on hospital-diagnosed mental disorders and mortality. Poisson regression was applied to estimate independent and joint associations with mortality, interaction contrasts and attributable proportions.

A total of 162 497 individuals were followed for 886 614 person-years, and 9047 individuals (5.6%) died during follow-up. Among men, interaction between mental disorders and loneliness, social isolation and low social support, respectively, accounted for 47% (95% CI: 21–74%), 24% (95% CI: −15 to 63%) and 61% (95% CI: 35–86%) of the excess mortality after adjustment for demographics, country of birth, somatic morbidity, educational level, income and wealth. In contrast, among women, no excess mortality could be attributed to interaction. No clear trends were identified according to age or characteristics of the mental disorder.

Mortality among men, but not women, with a co-occurring mental disorder and social disconnectedness was substantially elevated compared with what was expected. Awareness of elevated mortality rates among socially disconnected men with mental disorders could be of importance to qualify and guide prevention efforts in psychiatric services.