Be happy for a healthy heart

“Women laugh their way to health,” the headline in the Daily Mail declares. The news story underneath reports that scientists have found that “happy women may be at lower risk of problems such as heart disease, cancer, high blood pressure and obesity.”

The newspaper report is based on a study that looked at the association of mood during the day with levels of cortisol (the “stress hormone”) and two proteins the levels of which increase during inflammation. This study did not look at how mood affected long term the development and progress of continuous conditions like  heart disease and cancer. Any link between a higher level of cortisol or either of the inflammatory proteins to the future risk of problems such as heart disease is a tenuous one.

Where did the story come from?

Dr Andrew Steptoe and colleagues from University College London carried out this research. The study was funded by the Medical Research Council, British Heart Foundation, Health and Safety Executive, the Department of Health in the UK, and the National Heart, Lung, and Blood Institute, National Institute on Aging, Agency for Health Care Policy Research, and the John D. and Catherine T. MacArthur Foundation in the US. It was published in the peer-reviewed: The American Journal of Epidemiology .

What kind of scientific study was this?

This was part of a large study started in 1985 (the Whitehall II study) that looked at risk factors for heart disease in a sample of over 10,000 UK civil servants. This new cross-sectional study aimed to look at how people’s moods affected their levels of the hormone cortisol in the saliva (a stress marker) and also how it affected two proteins, C-reactive protein (CRP) and interleukin-6 (IL-6), involved in the body’s inflammatory response.

The researchers asked the 6,483 participants of the Whitehall II study who attended a medical between 2002 and 2004 to take part in the new study. Participants were aged between 50 and 74 and during the medical the participants gave blood, had measurements such as their height and weight taken, and provided information on their lifestyle and other aspects of their lives, such as income, whether they were married or if they smoked. They also filled in a standard questionnaire (the CES-D scale) to assess whether they had experienced any symptoms of depression in the past seven days, and if so, how often.

Participants were asked to collect six saliva samples on a single day, at each of the following times: immediately after waking, 30 minutes after waking, two-and-a-half hours, eight hours, and 12 hours after waking, and just before they went to bed. They were also asked to rate how happy and content they felt just after taking each sample. Of the people asked to participate, 4,609 agreed and they posted their samples and records of how they felt to back to the researchers. Researchers then categorised how positive people’s moods were based on how often they reported being very or extremely happy. People who did not have any very or extremely happy responses were classified as having low positive mood, those with one or two were categorised as moderate, and those with three or above were categorised as high positive mood.

The researchers then tested participants’ saliva for cortisol. They assessed two aspects: firstly, how the cortisol levels changed between waking and 30 minutes after waking (called the cortisol awakening response), and secondly, the average cortisol measurements for the rest of the day. They also analysed the blood samples they collected for the two inflammatory proteins (CRP and IL-6). They then looked at whether people with different levels of positive mood had differing levels of cortisol or the two inflammatory proteins. They adjusted their analyses to take into account factors that may affect cortisol levels, such as age, sex, income, race, smoking, body mass index, waist-to-hip ratio, employment status, and time of waking. They also adjusted some of their calculations according to  how high people’s scores were on the CES-D, a scale that measures the presence of depressive symptoms.

What were the results of the study?

Researchers found that the more positive a person’s mood on the day of testing, the lower their average cortisol levels were during the day. This was not affected by their levels of depression (as assessed during their physical examination). There was no relationship between a person’s positive mood and cortisol level on waking, or the change between waking and 30 minutes later. The relationship between levels of the inflammatory proteins CRP and IL-6 and mood was different in men and women, so they were analysed separately. Women with low levels of positive mood during the day were more likely to have high levels of these inflammatory proteins than women with a high level of positive mood. This relationship between these proteins and positive mood was not found in men.

What interpretations did the researchers draw from these results?

The researchers concluded that the more positive a person’s mood the lower their levels of cortisol, and that this is independent of whether they are depressed or not, and of other factors known to affect cortisol levels. Also, in women, positive mood is associated with a reduction in the levels of inflammatory proteins in the blood.

What does the NHS Knowledge Service make of this study?

This study begins to investigate possible biological mechanisms by which positive mood might affect our health. We should consider these findings as preliminary for a number of reasons:

• Cortisol is a hormone that is released in everyone daily in a fluctuating rhythm (highest first thing in the morning). Levels may naturally be slightly different in each person, and also are increased for reasons other than stress, including low blood sugar levels, illness, exertion, pain or high temperature. These factors have not been considered by the study and therefore the cortisol level cannot definitely be attributed to the measurement of high or low mood in this study.
• It is also important to note that questions about mood, asking people how “happy, excited or content they feel at that moment”, are subjective; and how any two individuals rate what may be considered to be the same feeling is different. Just because one person doesn’t report feeling extremely happy at any time point, they cannot automatically be considered to have a low mood.
• The inflammatory proteins (CRP and IL-6) are general signs of inflammation that are elevated in a wide variety of conditions, including many arthritic conditions, autoimmune diseases, infections and cancer. Therefore, although they may be considered as markers of bodily “stress”, they relate to more than a person’s mood. The person may in fact be feeling low because of the other inflammatory or infective disease process that are occurring in their body, and which cause CRP and IL-6 levels to be elevated. Also, the measurement of the inflammatory proteins took place before the measurement of people’s mood, therefore their mood on the day of the study may not have caused the differences in the levels of the inflammatory proteins. 
• This study was conducted on one day. It is not clear how mood would be related to cortisol and inflammatory protein levels over a longer period. The authors note that one study over a five day period did not find an association between mood and cortisol levels, although they suggest that this may be related to differences in age between the participants.
• The participants in this study were all over 50, these results may not apply to younger people.

There is a long way to go to to understand how mood might affect our hearts, but even without a convincing biological association, a positive mood is surely something to be aimed for.