Thursday February 18 2010
“Being happy is a great way to keep your heart healthy,” reported the Daily Express. The newspaper quoted doctors who said that we should all have more fun to help avoid heart attacks.
The 10-year study assessed a range of symptoms, such as depression, hostility and anxiety, in almost 2,000 men and women. The participants were recorded in videotaped interviews and scored on their joy, happiness, excitement and contentment on a five-point happiness scale. For each point higher up the scale a person was placed, their risk of developing heart disease dropped by 22%.
It is plausible that happier people are healthier. However, the effect demonstrated in this study was quite small compared to traditional modifiable risk factors, such as smoking, blood pressure or bad cholesterol. Modifying each of these factors can independently reduce the risk of heart disease by more than a third, and the combined effect of improving them together is much greater. In comparison, the one-point improvement on the happiness scale used here produces a relatively small, but probably still important, decrease in risk.
Where did the story come from?
This research was carried out by Dr Karina W Davidson and colleagues from the Center for Behavioral Cardiovascular Health at Columbia University Medical Center in New York. The study was supported by multiple grants from the National Institutes of Health (NIH), National Center for Research Resources and NIH Roadmap for Medical Research in the US. The paper was published in the peer-reviewed medical journal European Heart Journal.
Many newspapers reported this story and interpreted the science fairly. All of them emphasised the benefits of a range of positive emotions. Some, including The Times, also quoted commentators, who said that this study does not prove ‘cause and effect’ and who recommended keeping established risk factors, such as smoking, blood pressure and cholesterol, under control.
What kind of research was this?
This was an analysis of data from a prospective cohort study conducted in Nova Scotia, Canada. The study aimed to see if positive emotions are linked to a lower risk of coronary heart disease (CHD). The researchers adjusted for several known heart risk factors and followed the population surveyed for up to 10 years. Only those who had completed the happiness questionnaires could be included in the analysis, and the five-point happiness scale was only recorded at the start of the study. It is possible that this could have led to inaccuracies in the estimate of the degree of benefit that happiness gives.
What did the research involve?
The researchers explain that previous studies have found a link between positive emotions and improved survival, immune function and lower risk of diabetes and hypertension. They say that negative emotions, such as anger, hostility and depression, are linked to a higher risk of a new episode of CHD.
The Canadian Nova Scotia Health Survey looked at the health of men and women aged 18 and older in 1995 and followed them for the next 10 years. The main outcome of interest was heart disease and death. The researchers used hospital discharge codes or death certificates to assess new fatal or non-fatal cases of heart disease. They said that Nova Scotia has a universal healthcare insurance system and the computerised recording of health records is near complete.
Only residents who had attended the first clinic session and completed the structured interview were included. Anyone who had had a hospital discharge diagnoses of CHD in the five years before the start of the study was excluded.
The participants’ sex, age, total cholesterol, HDL cholesterol, blood pressure, history of diabetes and cigarette smoking were recorded at the beginning of the study, and a nurse measured their weight and height. From the collected data, the researchers took the records of 1,739 participants (862 men, 877 women) for analysis from the 5,576 original records in the survey.
The researchers then used a range of interview scales to score emotions:
- Depressive symptoms were measured on the Centers for Epidemiological Studies-Depressive Symptoms (CES-D) Scale, using 17 items from a 20-item self-reporting scale.
- Hostility was assessed with the Cook-Medley Hostility Scale, which involved 50 true or false items commonly used to assess self-reported hostility.
- Anxious symptoms were assessed using the Trait-subscale of the State-Trait Anxiety Scale, a 20-item test that describes symptoms of anxiety (such as, I worry too much over something that really does not matter).
- Positive affect (happiness) was scored using video of a 12-minute structured interview designed to be stressful. In the interview, researchers assessed how participants expressed emotions and stress reactions. Positive affect is a rating of the degree to which participant express positive emotions, whether verbally, in their behaviour (such as smiling) or in the tone of responses (such as cheerful). After the end of the interview, the tapes were coded from one (no positive affect expressed) to five (extreme positive affect) by 23 certified coders.
What were the basic results?
The researchers adjusted their results for traditional risk factors, including age, sex, blood pressure and cholesterol, and for negatives affects such as depression and hostility. They found that the rate of new episodes of CHD was 22% lower for a one-point increase in the positive affect score (adjusted hazard ratio [HR] 0.78, 95% confidence interval [CI] 0.63 to 0.96).
When the researchers compared people with high happiness scores to those with lower scores, they found that those with higher scores were reportedly more likely to be female, less likely to be current smokers, and more likely to have lower total cholesterol, blood pressure, levels of hostility and anxious symptoms. The researchers say that this “suggests that higher levels of positive affect are related to better overall health”.
How did the researchers interpret the results?
The researchers say that, in this large randomly selected sample, increased positive emotions (happiness) were associated with a reduced risk of new heart attacks over 10 years, even after adjustment for depressive symptoms, hostility and anxiety.
According to the researchers, the prospect that increasing happiness is associated with a decrease in the risk of heart disease is an exciting, but untested, theory that needs further research.
This study tested a theory that many people already accept without any strong evidence: that being happy is good for the heart. This research appears to show a link between happiness and heart disease, at least in the context of recorded interviews as an assessment of happiness.
The researchers warn that better heart health may simply be related to better overall health in people who are happy. Some other limitations are also mentioned:
- As the information on cardiovascular risk factors was only measured at the start of the study, some misclassification is likely. Some people may have developed high blood pressure or started smoking during the 10 years of follow-up.
- As the electronic records did not exist before 1990, it is technically possible that some participants who experienced CHD events more than five years before the study could have been included in the analysis if they had denied or forgotten about their past heart disease.
- As this was an observational study, the researchers say that they cannot rule out the possibility that factors they did not measure or did not fully adjust for could have caused the effect thought to be due to happiness. They say that the participants selected for the study were generally younger, female and less hostile than the participants who were excluded from the analysis. They say that it is “possible that our results may be at least partially accounted for by a selection bias”.
Overall, this study provides useful data and illustrates the way that happiness can be measured relatively objectively in studies of emotions. The link between happiness and heart disease is not completely clear and the wide confidence intervals in the statistical analysis suggest that, if the selection bias is taken into account, the effect of happiness may be quite small.
It is plausible that happier people are healthier. However, the actual effect demonstrated in this study was quite small, compared with traditional modifiable risk factors, such as smoking, blood pressure or bad cholesterol. Modifying each of these factors can independently reduce risk by more than a third, and the combined effect of improving them together is much greater. In comparison, the one-point improvement on the happiness scale used here produces a relatively small, but probably still important, decrease in risk.