In this large, randomly selected population-based study, increased positive affect was associated with a reduced risk of 10-year incident CHD, even after adjustment for depressive symptoms, hostility, and anxiety. To our knowledge, this is the first prospective study to examine this relationship.
Recent studies have begun to explore the protective effects of positive affect on physical health, including cardiovascular risk factors such as hypertension and diabetes.1–3
Prospective observational studies have reported an inverse association between positive affect and incident stroke32
and mortality in medical in-patients33
as well as diabetic patients,34
and others have shown that positive affect is protective against recurrent major clinical events in patients with cardiac stents.35
In the largest study to date, the Whitehall II cohort study did not find evidence of positive affect protecting against incident CHD, independent of negative affect.36
However, these studies utilized measurements of positive affect that were not ideal.37
In fact, some of these studies measured positive affect using instruments that were designed to assess depressive symptoms. In this analysis, trained observers estimated levels of positive affect rather than relying on self-reported levels or items originally designed to assess negative affect.
Positive affect, joy, happiness, and excitement, have previously been shown to be largely independent of negative affect.9
In our data, there was also a negligible correlation between positive affect and depressive symptoms. We had previously found that depressive symptoms were a significant predictor of CHD incidence in this sample, and so thought it was important to control for this important psychosocial risk factor.38
Our findings are consistent with an independent and clinically relevant relationship between CHD and positive affect (22% relative risk reduction for each one-point increment in positive affect on a five-point scale), a relationship that was not attenuated by adjustment for depressive symptoms.
Possible pathophysiological mechanisms
Various mechanisms may explain the potential cardiovascular benefits of higher levels of positive affect. For example, positive affect, but not negative affect, has been shown to predict enhanced parasympathetic modulation of heart rate.39
Positive affect is associated with blunted SBP, DBP, and norepinephrine reactivity during a standardized, stressful laboratory task and with lowered 30 min post-awakening cortisol levels in these same subjects.40
Increased positive affect may protect against CHD via improvements in sleep habits and smoking cessation. Steptoe et al
have found that higher positive affect is predictive of better sleep quality, independent of negative affect and other predictors of poor sleep, and Strong et al
found that higher levels of positive affect are associated with fewer urges to smoke during smoking cessation treatment, independent of levels of negative affect. However, further research is needed to explain the mechanisms by which positive affect might confer long-term CHD protection.3,43
Among the limitations of our analysis is the fact that information on cardiovascular risk factors were only measured at baseline and therefore, some misclassification is likely. Over the duration of follow-up, it is likely that patients experienced changes in their cardiovascular risk factors (e.g. development of diabetes), health behaviors (e.g. changes in physical activity or smoking status) and medications (e.g. starting or stopping cardio-protective drugs). However, this misclassification would likely have been non-differential and would lead to an underestimation of results. Similarly, levels of positive affect were also only measured at baseline and changes may have occurred over the 10 years of follow-up. First impressions of positive affect, even by strangers, are remarkably reliable and are in high agreement with ratings done by trained coders, life partners, clinicians, the person, and close friends.44
These ratings are also remarkably stable across decades of adulthood.45
It nevertheless remains possible that misclassification occurred, which again would have led to underestimation of the protection conferred by positive affect.
We aimed to exclude survey participants with pre-existing CHD. Therefore, we excluded participants with any self-reported CHD or CHD events documented in the patient charts for the 5 years prior to the survey date. However, since electronic records did not exist prior to 1990, it is not possible to obtain information farther back. Therefore, some participants who may have experienced prior CHD events more than 5 years before the baseline survey and denied a history of CHD may have been included in the current analysis. If those who experienced CHD events more than 5 years prior to the baseline visit were also more likely to demonstrate lower levels of positive affect, the results may be an overestimate of the true association.
Since this is an observational study, we cannot rule out the possibility of unmeasured or residual confounding. Participants with data available on positive affect were younger, less likely to be male, less likely to be hostile, and had higher blood pressures than the participants without positive affect scores who were excluded from this analysis. If those who were excluded differed greatly in their risk of CHD and also in their (unknown) levels of positive affect, it is possible that our results may be at least partially accounted for by a selection bias. Therefore, confirmatory studies are needed. Strengths of our analysis include the relatively large sample size, use of a structured interview with standardized assessment of positive affect, inclusion of standard negative affect scales as covariates, and long-term follow-up.
Conclusions and clinical implications
In summary, in this prospective population-based study, we found that positive affect was independently associated with risk of CHD. The positive affect we assessed is relatively easy to judge in a clinical situation. Does the patient smile and appear able to enjoy some aspects of life during the clinical interview or medical history taking? Do they report that they experience pleasure or excitement with some parts of their daily life? Assessment of positive affect may complement evaluations for CHD risk that only assess negative emotions such as depression.
Potential interventions to augment positive affect are usually labelled behavioral activation interventions,46
in which a patient notes which hobbies, daily activities, or other habits are enjoyable, with instructions to pursue those activities with increased and documented daily frequency. Conducting such a simple intervention results in patient-reported increases in quality of life. In fact, most successful depression interventions include increasing positive affect, as well as decreasing negative affect, as key components to psychotherapy.47
Furthermore, a recent study reports that the use of antidepressants without psychotherapy can result in lower levels of positive affect.48
Randomized controlled trials directly increasing positive affect in cardiopulmonary patients are now underway.49
However, as we report findings from an observational study, we do not yet have evidence to suggest that regular assessment of positive and negative affect should be recommended. Whether increasing positive affect would decrease the risk for CHD is an exciting, but as of yet untested hypothesis, remaining to be addressed.