Researchers publishing in BMC Geriatrics have found that people who reported being happy were considerably more likely to live longer than people who were not.
Conflicting previous research
The relationship between happiness and health, even controlling for other relevant factors, has been frequently confirmed and occasionally denied in the research. While a comprehensive review has found a very significant association , another study found that controlling for physical activity and prevalent morbidity was sufficient to remove the statistical association between happiness and reduced mortality . The fact that not all happiness-related studies ask the same questions muddies the waters, making it unclear how they should be compared.
A robust, mostly happy cohort
This study used two combined cohorts that consisted over 6,000 Singaporean adults who were at least 55 years old and dwelling in senior communities. The researchers note that Singapore is home to a wide variety of Asian ethnicities, and they have indicated that their research applies to every group involved in this study.
The participants were asked a simple question: how happy are you? A scale consisting of five possible options, from “very happy” to “very sad”, was offered. About three-fifths of respondents reported “fairly happy”. Only about a fifth responded neutrally, “fairly sad” was at 1.4%, and “very sad” was at 0.3%, with “very happy” being nearly a fifth.
After 71,337 person-years of observation, just over a sixth of the very happy participants had died, compared to over a fifth of the fairly happy, about a fourth of the neutral, two-fifths of the fairly sad, and nearly half of the very sad. This represents a very strong correlation with a very small p-value.
While these results held true when they were controlled for age, sex, and ethnicity, they were not corroborated when many psychiatric health conditions were controlled for. However, as the researchers note, there is strong overlap: people with such conditions are highly unlikely to be happy. Controlling for cognitive impairment still gave strong results, and while controlling for physical problems reduced the strength of the results, they were still within statistical significance.
Our results suggest that it cannot be disentangled from a broader construct of psychological wellbeing and holistic health. It is therefore unsurprising that the presence of depression and self-perceived health and functioning should explain almost all the relationship between happiness and mortality.
Unlike other studies , these researchers found no gender differences in their results: men and women were equally affected. The researchers also note that, unlike many other studies in this area, the researchers used a single metric rather than multiple, which may have altered the results.
Chicken or egg?
This is an association study, not a causation study. Health and happiness are obviously closely related, but the nature of that relationship is not clear. The researchers assert that “Happy people are healthy people”, but it is not clear just how much health leads to happiness and happiness leads to health. It is very plausible that the association is bidirectional: each one contributes to the other.
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 Diener, E., & Chan, M. Y. (2011). Happy people live longer: Subjective well-being contributes to health and longevity. Applied Psychology: Health and Well-Being, 3(1), 1-43.
 Koopmans, T. A., Geleijnse, J. M., Zitman, F. G., & Giltay, E. J. (2010). Effects of happiness on all-cause mortality during 15 years of follow-up: The Arnhem Elderly Study. Journal of Happiness Studies, 11, 113-124.
 Martín-María, N., Miret, M., Caballero, F. F., Rico-Uribe, L. A., Steptoe, A., Chatterji, S., & Ayuso-Mateos, J. L. (2017). The impact of subjective well-being on mortality: a meta-analysis of longitudinal studies in the general population. Psychosomatic medicine, 79(5), 565-575.