Ruut Veenhoven of Erasmus University Rotterdam analysed 30 follow-up studies on happiness and longevity found that happiness does not predict longevity in sick populations, but that it does predict longevity among healthy populations.
So, happiness does not cure illness but it does protect against becoming ill. As a result, happy people live longer. The size of the effect on longevity is comparable to that of smoking or not.
There have been more reports of happy people living longer, but for long it was unclear whether happiness causes longevity, since it can also be that good health adds both to happiness and longevity.
Scientists assess causality using long-term follow-up studies, taking initial health into account. The results of such studies seemed contradictory; several studies found the expected causal effect of happiness on longevity, but other studies found no effect and some observed even earlier death among the happy. The analysis of 30 follow-up studies showed that the difference is in the people under investigation.
Happiness does not lengthen the life of seriously ill people, but it does prolong the life of healthy people. Happiness appears to protect against falling ill. One of the mechanisms behind that effect seems to be that chronic unhappiness causes stress, which on its turn reduces immune response.
Another possible mechanism is that happiness adds to the chance of adopting a healthy life style.
An implication of this finding is that wider public health can also be promoted by policies that strengthen individual life-abilities and improve the livability of the social environment.
BE Happy and Have a Great Day, Everyday!
Veenhoven R. Healthy happiness: effects of happiness on physical health and the consequences for preventive health care. Journal of Happiness Studies, 2008; 9 (3): 449-464
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