Social Network Cultivation, Diurnal Cortisol, and Telomere Length: Testing the Rejuvenation Hypothesis

The hypothalamic–pituitary–adrenal (HPA) axis plays an important role in homeostatic and allostatic adjustments to environmental challenges. However, how stress and aging affect the level of cortisol, the end product of this neuroendocrine axis, is not completely understood (Chahal & Drake, 2007). In a pioneering study of the factors integral to the relationship between successful aging and cortisol, the PI and his associates (Lai et al., 2012; Lai, Evans, & Chong, 2017) found that Chinese elders who spent more time and effort cultivating their social relationships with family, relatives, friends, and neighbors exhibited lower levels of diurnal cortisol in the saliva and a steeper diurnal decline. This specific diurnal rhythm of cortisol, characterized by lower diurnal levels and more effective deactivation of the HPA axis, has also been observed in younger age groups in prior studies (e.g., Ice, 2005; Kumari et al., 2010) and a recent study by the PI and his associates (Lai, Leung, Lee, Lam & Berning., 2018). An earlier study of 2,120 Chinese elders in Hong Kong showed that the cultivation of social ties predicted successful aging (Chong et al., 2012). Thus, the findings reported by Lai et al. (2017) can be taken to imply that those who grow old more successfully may be biologically younger than their peers. This idea has been coined the “rejuvenation hypothesis” (Lai & Lee, in press).Despite the significance of these findings, the psychological mechanisms that translate positive social motivation into a younger diurnal cortisol profile have not been identified. Moreover, the potential effect of a younger cortisol profile on health has not been adequately addressed. The proposed study will aim to bridge these knowledge gaps by testing the rejuvenation hypothesis. We predict that a stronger motivation to cultivate social ties will serve to enhance social embeddedness. We expect that this in turn will rejuvenate the diurnal cortisol profiles of older individuals and increase their telomere length, an index of cellular aging (Tomiyama et al., 2012). As cortisol (Fried & Walston, 1999; Sapolsky, Krey, & McEwen, 1986; Spiegel & Sephton, 2001) and telomere length (e.g., Njajou et al., 2009) are crucial biomarkers of health and aging, the findings of the proposed study will inform the composition of effective intervention programs and social policies for promoting health and successful aging in the elderly.