Leading a happy life means you are less likely to develop heart disease, according to research published today.
The team behind the study – who believe it is the first to show an independent relationship between positive emotions and heart disease – said it could have major implications for improving people's health, suggesting it might be possible to help prevent the condition by boosting people's good feelings.
The researchers followed 1,739 healthy adults over 10 years, assessing their risk of heart disease and measuring symptoms of depression, hostility and anxiety, as well the degree of expression of positive emotions, known as "positive affect". Positive affect is defined as the experience of pleasurable emotions such as joy, happiness, excitement, enthusiasm and contentment.
The team, from the Columbia University Medical Centre in New York, found that over the decade, increased positive affect led to a lowering of risk of heart disease by around a fifth at each point on a five-point scale measuring levels of happiness, ranging from "none" to "extreme". So those who had no positive affect were at a 22% higher risk of heart disease than those with a small positive affect, who were themselves at a 22% higher risk than those with moderate positive affect. The findings took account of age, sex and heart-associated risk factors.
The study's lead researcher, Karina Davidson, said: "We desperately need rigorous clinical trials in this area. If the trials support our findings, then these results will be incredibly important in describing specifically what clinicians and patients could do to improve health."
The study, published in the European Heart Journal, said that positive affect is largely independent of negative affect, so someone who is generally happy and contented can also occasionally be anxious, angry or depressed.
"We also found that if someone who was usually positive had some depressive symptoms at the time of the survey, this did not affect their overall lower risk of heart disease," Davidson said. "As far as we know, this is the first prospective study to examine the relationship between clinically assessed positive affect and heart disease."
There are several possible explanations, according to lead researcher Karina Davidson. Happier people may have longer periods of rest or relaxation, which puts less pressure on their bodies' automatic reflex activities. They may also recover more quickly from stressful events and spend less time reliving them, which seems to cause physiological damage itself.
Davidson said people should try to inject some fun into their daily routines, rather than only allowing themselves to enjoy life in short bursts."Some people wait for their two weeks of vacation to have fun, and that would be analogous to binge drinking," she said. "If you enjoy reading novels, but never get around to it, commit to getting 15 minutes or so of reading in.
"If walking or listening to music improves your mood, get those activities in your schedule. Essentially, spending some few minutes each day truly relaxed and enjoying yourself is certainly good for your mental health, and may improve your physical health as well."
The British Heart Foundation (BHF) said the study showed an unprecedentedly clear link between happiness and a lower risk of developing heart disease.
"The BHF is funding science to unravel the biology that underlies this link," Ellen Mason, the foundation's senior cardiac nurse, said. But she added that the study did not prove cause and effect or say for sure whether changing mood could reduce the risk.
"This research suggested that those who naturally had a 'glass half- full' mood seemed to be most protected from disease," she said. "But we're not all like that, and we know that improving your mood isn't always easy – so we don't know if it's possible to change our natural levels of positivity."
Mason recommended that people took time to indulge in healthy activities that could lift their mood, but said keeping established risk factors under control remained crucial.