Marriage quality and heart health go under the microscope in a new study.
Over the years, the health-protective powers of marriage have been put to the test numerous times.
Although some scientists have concluded that marriage increases longevity and reduces health risks, there is still fierce debate as to whether or not this relationship is genuine.
Some argue that the effect may be due to bias by selection into marriage. In other words, it may be that healthier people are more likely to marry.
If the beneficial effect of marriage is genuine - and many believe that it is - it may be because partners support and encourage positive behaviors. It may also be because a close relationship helps to buffer stress.
If these factors are behind the protective effect, assessing the quality of a marital relationship over time would show the effect of marriage without the influence of marital bias.
Put simply, studying individuals who are in varying qualities of marriages will help us to understand whether it is actually an effect of being married or simply due to the average health status of people who get married.
A study published this week in the Journal of Epidemiology & Community Health uses this approach to take a fresh look at the age-old hypothesis.
As the authors explain, "Studies of the effects of relationship quality within marriages control for marriage selection, allowing investigation of the protective effects of partnership in isolation."
Marriage quality and health over time
In total, the researchers used 19 years worth of data from the Avon Longitudinal Study of Parents and Children. While earlier studies have primarily focused on cardiovascular disease at a single point in time, in this study, a longitudinal approach was used.
Using data taken across almost two decades, the team specifically looked at the links between relationship quality over time and cardiovascular risk in married men.
Cardiovascular risk was chosen as a measure because it is a common health issue and is relatively well understood. They opted to study men because, in middle age, men have a greater cardiovascular risk than women, displaying differences in risk factors earlier on.
The fathers involved in the study completed questionnaires that assessed their relationship quality when their children were aged 3, and then when they were aged 9. Relationships were ranked as "consistently good," "consistently bad," "improving," or "deteriorating."
These data were taken when their children were aged 19; the large time period between measures gave cardiovascular risk factors enough time to develop in response to changes in relationship quality.
Data were controlled for a range of factors, including height, age, education level, and household income.
There was little change in the cardiovascular risk factors for men who reported consistently good or bad relationships, but there was a small effect for those whose relationship quality had changed. The differences were relatively slight, but they were significant.
The impact of ups and downs
Compared with men whose relationships were constantly good, those whose relationships were ranked as improving had lower levels of low-density lipoprotein, or "bad" cholesterol, and a lower body weight (an average of 1 BMI unit).
There were also small improvements in cholesterol levels and diastolic blood pressure, which is a measure of cardiovascular risk. Conversely, individuals in worsening relationships were found to have significantly worse diastolic blood pressure.
The study authors concluded:
"Changes in the quality of a marital relationship appear to predict CVD [cardiovascular disease] risk, though consistently good or poor relationship groups were not very different."
It is interesting that no differences were measured in men whose relationships remained stable, be that good or bad. The team believes that this might have been down to "habituation" - or getting used to what you have - or differences in the way that some people perceive the quality of their relationship.
As with any study, there are gaps that need further probing. For instance, this is an observational study so it cannot prove cause and effect. Also, there were a large number of participants who dropped out across the duration of the study, and, of course, it only looked at men.
However, the research adds some interesting data to a debate that has been rumbling on for many years. More research is always needed, but, with the ongoing interest in this question, more research is sure to come.