The present study used a multimodal assessment of engagement in social relationships, and nocturnal BP profiles in a community-based sample of African–American and white men and women. We found that more socially isolated individuals, as assessed via questionnaire and daily diary methods, were more likely to show higher nocturnal/day BP ratios as compared to their more socially engaged counterparts and these results persisted even after statistically controlling for a host of demographic and general health characteristics (i.e. hypertension diagnosis, use of cardiac medications, elevated clinic BP, BMI, perceived health, health behaviors), and PSG-assessed and actigraphy-assessed sleep variables that had the potential to account for the associations.
In addition, ours was the first study to examine the association between nocturnal BP and a diary measure of social contact frequency assessed simultaneously with the BP assessment, as well as a questionnaire measure of social integration, assessed more than a year prior to the ambulatory BP assessment. Despite the difference in timing of these measures and the fact that they measure distinct, though related aspects of social networks, they showed a modest correlation with each other, and were both independently associated with nocturnal BP profiles. However, the diary measure of social contact frequency was a stronger correlate of nocturnal BP than social integration, which may reflect both the ecologic validity of the measure as well as the fact that it was measured concurrently with the BP assessment. Moreover, measuring ‘in-vivo’ social contacts may indeed provide a more sensitive measure of how social relationships influence cardiovascular morbidity and mortality.
We found inconsistent evidence regarding the degree to which ethnicity moderates the association between social relationships and nocturnal BP. Specifically, the ethnicity interaction term was nonsignificant in the social integration model; however, for the diary measure, the association between frequency of social contacts and nocturnal BP was stronger among African–Americans compared to whites. African–Americans also reported less frequent social interactions on the diary measure but not on the integration measure. Thus, these findings may reflect greater variability in social contact frequency among African–Americans and/or greater susceptibility to the health benefits of social contacts, or alternatively, the health risks of social isolation. Indeed, among African–Americans, the most socially isolated individuals (lowest tertile) were roughly five times more likely to be categorized as nondippers (according to the frequently used cut-point of <10% day-to-night BP decline) as compared to the most engaged individuals (highest tertile).
Although there was a similar trend among whites, the effects were less pronounced. Interestingly, a recent study by Cooper and colleagues [12
] on perceived social support and nocturnal dipping found virtually the opposite effect of ethnicity. Specifically, their results showed a significant relationship between higher levels of social support and greater nocturnal BP dipping in whites, but in African–Americans, higher social support was associated with less dipping. These contradictory findings may be due to the fact that the former study measured the perception of social support, whereas our study measured the scope and variety of social contacts, which are related but distinct constructs. Taken together, these findings highlight the need to consider multiple aspects of the social environment as they relate to cardiovascular outcomes in diverse sociocultural contexts.
These results must be interpreted in the context of the study’s limitations and strengths. On the basis of the study recruitment criteria the sample included older African–American and white men and women, and we excluded individuals with a previously diagnosed sleep disorder. Thus, our findings may not generalize to sleep clinic patients, younger populations, or other minority groups. Limitations associated with our social relationship measures include the timing of the assessment for social integration and the fact that we did not assess the quality of those relationships or the functional aspects of support (e.g. emotional, tangible). In addition, the frequency of ambulatory BP monitoring was lower than is common in clinical practice; however, given that our study included 48 h of recording versus the traditional 24 h, these are likely to be representative estimates of day and night BPs [24
]. Whereas this is the first study to show an independent association between social relationships and nocturnal BP after controlling for a host of potential nocturnal pathways, we did not include measures of all possible confounders, including measures of hypothalamic-pituitary-adrenal activity, inflammatory, hemostatic markers, or other psychosocial risk factors. Given previous associations between these factors and both nocturnal BP [25
] and social relationships [28
], it is plausible that these or other unmeasured variables may account for the findings. The effect sizes for social integration and social contact frequency were relatively small, accounting for 2–4% of the unique variance in night/day MAP ratio; however, these effects were roughly comparable to the effect size for all of the demographic, clinic, and health behavior covariates combined (9%). Finally, the cross-sectional and observational nature of the study precludes inferences regarding causality.
Strengths of the study include the fact that this was a diverse sample from a community-based epidemiological study of African–American and white men and women, increasing the generalizability of the study findings to the nonpatient population at large. In addition, the study’s inclusion of multiple methods for assessing social relationships and sleep, and statistical adjustment for other factors that may account for observed associations, strengthens the contention that there is an independent association between social relationships and nocturnal BP.
Ambulatory BP monitoring has become increasingly recognized as a critical component of the clinical management of hypertension, owing in part, to the growing recognition of the independent, prognostic significance of nocturnal BP. Elucidating potential, modifiable risk factors for nocturnal BP nondipping has the potential to identify novel treatment targets in populations at high-risk for CVD or in those with poorly managed manifest CVD. For the past two decades, compelling research has documented the profound effects of the social environment on cardiovascular morbidity and mortality. The current findings extend this literature by showing robust, independent relationships between social integration and frequency of social contacts and nocturnal BP in a community sample of African–American and white men and women. Incorporating a brief assessment of patients’ engagement in social relationships either in conjunction with symptom monitoring or via brief questionnaire may provide useful social data of prognostic value in a clinical setting, and this may be particularly important among African–Americans. In summary, the findings suggest that social connections or the lack thereof may influence key prognostic indicators of CVD, including nocturnal BP, which may inform our understanding of how social relationships contribute to cardiovascular health.