Social integration of daily activities and cortisol secretion: a laboratory based manipulation.

A diverse body of literature suggests that social contacts have direct regulatory influences on biological rhythms such as the diurnal cortisol decline. Although our previous prospective research has found a link between social contacts and cortisol secretion, a manipulation of social contacts is necessary to definitively evaluate causality. The current study involved a laboratory-based manipulation of daily social contacts. Fifty-three females experienced both high and low social contact conditions in the lab while collecting ambulatory data on their social contact and cortisol levels. Data were analyzed using hierarchical linear modeling, such that cortisol production on high social contact days was compared within person to cortisol production on low social contact days. Although the manipulation successfully altered daily social contacts, it had no significant effect on cortisol slope. However, cortisol slope differences were significant when participants had contact with someone whom they usually saw every day. Social relationships that provide daily contact may have the strongest influence on biological rhythms.