According to a large population study in Sweden, first-born children have a lower risk of cardiovascular events than brothers and sisters born later, but people who are part of a large family with many siblings have an increased risk of these events. The findings were published in the online journal BMJ Open.
While the influence of family history – that is, the health of parents and grandparents – on a person’s health, including cardiovascular risk, is well known, there is now growing interest in how the make-up of a person’s immediate family influences health.
For their large population study, the authors drew on data on 1.36 million men and 1.32 million women born between 1932 and 1960 and aged 30–58 years in 1990 from the Multiple-Generation Register in Sweden. They retrieved data from national registers on fatal and non-fatal cardiovascular and coronary events over the next 25 years.
Analysis of the data showed that first-borns had a lower risk of non-fatal cardiovascular and coronary events than siblings born later. First-born men had a higher risk of death than second and third-born siblings, while first-born women had a higher risk of death than second-born siblings, but equal to further siblings.
Looking at family size, compared with men with no siblings, men with one or two siblings had a lower risk of cardiovascular events, while those with four or more siblings had a higher risk.
Similarly, compared with men with no siblings, men with more than one sibling had a reduced risk of death, whereas those that had three or more siblings had an increased risk of coronary events.
A similar pattern was seen in women. Compared with those without siblings, women with three or more siblings had an increased risk of cardiovascular events, while those with two or more siblings had an increased risk of coronary events. Women with one or more siblings had a lower risk of death.
Since this was an observational study, it cannot establish cause. The authors also noted some limitations, including that the Swedish registers included no information on diagnostic procedures and there no data were available concerning lifestyle factors, such as body mass index, smoking and diet.
The researchers took into account socioeconomic status, obesity, diabetes, chronic lung disease (COPD) and alcoholism and related liver disorders. They also note that some of their findings conflict with those from previous studies.
The researchers noted that, given the wide variation among countries of policies to support families and the number of children, their findings could have implications for public health.
“More research is needed to understand the links between sibling number and rank with health outcomes,” they say. “Future research should be directed to find biological or social mechanisms linking the status of being first born to lower risk of cardiovascular disease, as indicated by our observational findings.”
Source: BMJ Open
Journal information: Sibling rank and sibling number in relation to cardiovascular disease and mortality risk: a nationwide cohort study, BMJ Open (2021). DOI: 10.1136/bmjopen-2020-042881
