Besides a family history of CVD largely influenced by genetic predisposition, there is also evidence to show that family structure, especially birth order but not family size, can influence the risk of death due to cardiovascular conditions.
However, only a few studies have looked at the impact of family structure on nonfatal cardiovascular events.
A comprehensive understanding of the impact of family structure on CVD risk requires the inclusion of both fatal and nonfatal cardiovascular events.
A large observational study involving people aged 30–58 years at onset now shows that the number of siblings and birth order can influence the risk of total cardiovascular events over a 25-year follow-up period.
A team of researchers led by Prof. Peter Nilsson at Lund University in Sweden conducted this study. Their findings appear in the journal BMJ Open.
To obtain information about family structure, the researchers used the Swedish Multi-Generation Register (MGR). The register includes records of biological parents of more than 95% of the population born after 1931 and alive in 1961, thus providing an exceptionally large dataset.
The study included data from 1.36 million men and 1.32 million women aged 30–58 years in 1990. They determined the risk of nonfatal and fatal cardiovascular events as well as total mortality among these individuals using data from death and hospital discharge registers between 1990 and 2015.
Factors such as socioeconomic status, education level, marital status, and medical conditions such as diabetes can influence CVD risk.
The team adjusted their analysis to account for the influence of these variables and isolate the impact of family structure on cardiovascular events.
In terms of family size, men and women with more than one sibling were at a lower risk of death than those with no siblings.
Men with one or two siblings had a lower risk of cardiovascular events than those with no siblings, while those with four or more siblings had a higher risk.
Men with three or more siblings also had a higher risk of coronary events compared with no siblings.
Similarly, compared with women with no siblings, women with three or more siblings had a higher risk of cardiovascular events. In addition, women with two or more siblings had a higher risk of coronary events.
In the case of birth order, first-born individuals had a lower risk of cardiovascular and coronary events than those who were born later.
In contrast, first-born individuals had a higher risk of overall mortality than second-born siblings.
The researchers point out that “more research is needed to understand the links between sibling number and rank with health outcomes.”
While the study’s strengths included a large sample size and comprehensive data on family structure and hospital records, it also had some limitations.
The researchers note that the study, owing to its observational design, only shows a correlation between family structure and cardiovascular events and does not establish causation.
Due to the lack of data, the researchers were also unable to account for variables such as diagnostic procedures, parental socioeconomic status, smoking, diet, and other lifestyle factors that could have influenced their analysis of CVD risk.
Since social factors are likely to contribute to the impact of family structure on health outcomes, including cardiovascular risk, the study’s results could influence public health policy.
Significantly, this study was conducted in Sweden, which has a generous welfare system. The authors observe that “this is of public health interest as different countries endorse different policies to support families and number of children.”
“Future research should be directed to find biological or social mechanisms linking the status of being first born to lower risk of CVD, as indicated by our observational findings,” state the authors.