by George BISHOP
t is common in everyday conversation for people to link emotional states with cardiovascular health. We may speak of someone “dying of a broken heart” after he or she has been bereaved or experienced a major disappointment. People also sometimes say that someone “had a coronary” when that person is angry or outraged over something. A large amount of research backs up these observations in showing that bereavement is associated with higher cardiovascular death rates soon after the bereavement takes place, and anger and hostility are associated with acute increases in heart rate and blood pressure with these cardiovascular responses, which in turn relate to an increased risk of heart disease.
Almost all of the research showing the association of anger and hostility to cardiovascular responses has been done in North America and Europe and mostly with Caucasian populations. Since there are also well-established cross-cultural differences in the way in which emotions are experienced and expressed, it has been unclear the extent to which these results would hold outside of those populations. To address this question, research in the Department of Psychology at NUS has been examining these relationships in Asian populations in Singapore.
In Singapore Context
Singapore is a particularly interesting locale for doing this type of research as Singapore’s ethnic mix allows for a comparison of groups that are culturally different and differ substantially in their cardiac death rates. It is a well-established fact that South Asians, including Indians in Singapore, die of heart disease at far higher rates than do many other groups, including Chinese and Malay Singaporeans. As such, we have been interested to test the relationship between stress and cardiovascular functions in these three ethnic groups.
Our results to date have been very intriguing. In an initial experiment in which Indian and Chinese males did computer tasks in the laboratory while being either harassed or allowed to do the tasks undisturbed – we found, similar to studies elsewhere, that when participants were harassed, they showed significant increases in blood pressure. However, we also found differences in the responses of Chinese and Indians.
Ethnic Comparisons in Trait Anger
For Chinese participants, those high in a personality measure of trait anger showed significant larger increases in blood pressure when they were harassed compared to when they were not, whereas those low in trait anger didn’t show this difference, a finding similar to what has been found in similar studies with Caucasians. For Indians, however, those low in trait anger showed the same kind of increase in blood pressure when harassed as did the Chinese participants who were high in trait anger while Indians high in trait anger showed strong increases in blood pressure to the tasks regardless of whether they were harassed. This is important because one of the hypothesized mechanisms by which anger and hostility are believed to be related to heart disease is via this type of cardiovascular reactivity. The basic idea is that over time these acute increases in blood pressure can cause damage to the interior lining of coronary arteries leading to an increase in atherosclerosis which in turn leads to heart disease. The fact that Indians low in trait anger showed increases in blood pressure when harassed and Indians high in trait anger showed increased blood pressure even when not harassed is consistent with the higher coronary heart disease (CHD) rates among Indians.
Ethnic Comparisons Using a Measure of Hostility
Our next studies found similar relationships with Singapore police officers. In one study, officers wore ambulatory blood pressure monitors while they went about their regular patrol duties. During the study, their blood pressure was taken approximately every 30 minutes. Each time the blood pressure was taken, the officers were asked to record their activities and what they were feeling using a questionnaire mounted on a palm-top computer. As expected, officers who had higher scores on a measure of hostility showed significant increases in blood pressure when they reported higher levels of frustration whereas those lower in hostility did not show this increase. Particularly interesting was the finding that whereas Indian officers showed a significant increase in blood pressure when they reported being angry, this was not the case for Chinese or Malay officers. Further, when reporting social interactions that caused them stress, Indian officers scoring high in hostility showed increases in their blood pressure whereas this was not the case for Indians low in hostility or for Chinese or Malay officers.
Sleep and During Waking Hours
These results are concerned with what happens to the blood pressure during the day when the person is awake and going about daily activities. We also have evidence for greater cardiovascular risk for Indians during sleep. It is well-known that blood pressure, like many other physiological functions, follows a diurnal cycle with blood pressure highest during waking hours and lowest in the early hours of the morning when the person is sleeping. This decline in blood pressure during sleep is sometimes referred to as nocturnal dipping and research shows that individuals showing reduced nocturnal dipping are at higher risk of heart disease. In a study of ambulatory monitoring of blood pressure among young Indian, Chinese, and Malay Singaporeans we had participants wear blood pressure monitors over a 24-hour period and were thus able to look at this phenomenon of blood pressure dipping. Our results showed that Indians high in trait anger show significantly less nocturnal blood pressure dipping than did other groups, again putting them at higher risk for various cardiovascular disorders. Evidence from our studies to date indicates that Indian Singaporeans show a pattern of cardiovascular responses to stress as well as reduced nocturnal dipping that is consistent with their higher rates of CHD but where do these differences come from? At this point, we do not have an answer.
One possibility is that the differences in cardiovascular responses that we have found are the result of cultural differences. Although little work has been done specifically comparing the experience and expression of emotions such as anger among Chinese, Indians and Malays, there is strong evidence that culture has a strong influence on how we experience and express emotions and it is possible that such differences are behind our observed differences in cardiovascular responses. Another very real possibility is that the differences may be genetic. We are currently examining both of these possibilities. One promising possibility related to emotional expression has to do with how people regulate their emotions with some of our preliminary data suggesting differences in how Chinese and Indians express or suppress their emotions under various circumstances. In addition, we are also looking at some of the genes known to be related to emotional experience. This work is in its beginning stages but preliminary indications are that some of these genes do differ by ethnic group and may help to explain some of the differences we have observed in cardiovascular responses.
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