Social strain and cortisol regulation in midlife in the US

► Negative social interactions may be a significant source of stress and could lead to altered diurnal cortisol rhythms. ► This study investigates the association between two waves (ten-years) of perceptions of social strain and cortisol rhythms in midlife. ► We find that reported levels of social strain were significantly associated with diurnal cortisol rhythm. ► These effects were more pronounced for individuals with a history of social strain across a ten-year period.