Is a happy marriage a double-edged sword for biological aging? Preliminary evidence for the moderating role of couples' health behaviors.

While happily married couples may age more slowly, the effect's magnitude varies widely. This variation could stem from partners' reinforcing each other's healthy and unhealthy behaviors. Grounded in symptom-system fit theory, we examined associations of marital quality (marital satisfaction and behavior) with biological aging in 107 middle-aged and older mixed-gender couples both cross-sectionally and over two years, assessing the moderating role of couples' health behaviors. Cross-sectionally, happier couples had lower T cell p16INK4a expression (B = -0.131, SE = 0.060, p = 0.0298). Nevertheless, slowed peripheral blood mononuclear cell (PBMC)-based DNA methylation (DNAm) aging and lower p16INK4a emerged only among happier couples who were more active (e.g., Bregion = -0.122, SE = 0.059, p < 0.05), slept better (e.g., Bregion = -0.136, SE = 0.064, p < 0.05), or ate healthier diets (Bregion = -0.080, SE = 0.040, p < 0.05). However, findings with marital satisfaction attenuated with multiple-test correction. Longitudinally, better marital quality predicted smaller rises in p16INK4a (B = -0.182, SE = 0.069, p = 0.009), but also shorter telomeres (B = -0.089, SE = 0.031, p = 0.006). Further, shortening telomeres and accelerated DNAm aging were driven by couples with both high satisfaction and poorer diet (e.g., Bregion = -0.046, SE = 0.023, p < 0.05) or sleep quality (e.g., Bregion = -0.050, SE = 0.024, p < 0.05). These longitudinal patterns persisted with multiple-test correction. The same patterns arose with inflammation: better marital quality predicted lower inflammation among couples with higher diet (Bregion = -0.075, SE = 0.037, p < 0.05) and sleep quality (Bregion = -0.280, SE = 0.139, p < 0.05), but higher inflammation among less active couples (Bregion = 0.140, SE = 0.070, p < 0.05) and those with poorer sleep (e.g., Bregion = 0.297, SE = 0.149, p < 0.05). These results begin to shed light on the literature's mixed findings-raising questions about the double-edged nature of happy marriages for immune health and aging, depending on the health behaviors they reinforce.