– Knowing how many siblings an individual has and whether they are the oldest child can be of great benefit in identifying whether there are increased risks of cardiovascular problems such as heart attacks and strokes. Future research should therefore focus on finding biological or social mechanisms that link the status of being firstborn to a lower risk of cardiovascular disease, as our observations show, says Peter M Nilsson, Professor of Clinical Cardiovascular Research at Lund University, who led the study, which is a collaboration with researchers at the Centre for Primary Health Care Research.
Identifies at-risk individuals
Today, at-risk individuals are identified, among other things, by asking patients about their family history and the presence of premature cardiovascular disease within the family, to get an indication of an increased risk of cardiovascular diseases. In the current study, the researchers chose to analyse another aspect of family patterns and instead studied siblings and their order and the biological, psychological, and social importance of this.
In Sweden’s national Multi-Generation Register, the researchers had access to data on 1.36 million men and 1.32 million women born between 1932 and 1960 who were between 30 and 58 years of age in 1990. They looked at the number of siblings and where the siblings were located. Adjustments were also made for the total number of siblings in relation to the birth order, where the risk of different outcomes was calculated using firstborns as a reference. The information was then linked to fatal and non-fatal heart attacks and strokes over a period of 25 years. In the analyses, the researchers also took into account and adjusted for socioeconomic status, obesity, diabetes, chronic lung disease (COPD) and alcoholism and related liver diseases.
Firstborns have lower risk
Among other things, the results indicated that individuals without siblings had an increased frequency of heart problems and that first-born children had a lower risk of heart problems such as heart attack and stroke. When the researchers looked at the size of the family and compared men without siblings to men with one or two siblings, they had a lower risk of cardiovascular events later in life, while those with four or more siblings were at a higher risk.
– Similarly, men with more than one sibling had a lower risk of death than men without siblings, while those with three or more siblings had an increased risk of coronary artery events. A similar pattern could be seen in women. Compared to those without siblings, women with three or more siblings had an increased risk of cardiovascular events, while those with two or more siblings were at an increased risk of coronary artery events. Women with one or more siblings had a lower risk of death, says Peter M Nilsson.
Can see the relationship but cannot explain it
The Swedish population registers do not contain data on diagnostic procedures, nor data on individuals’ lifestyle factors such as smoking and diet or body mass index (BMI). The researchers can see correlations but cannot explain them. For this, more in-depth data from biobanks, blood tests, and further analyses of various individual risk factors such as blood pressure, cholesterol and smoking are needed.
The researchers point out that the results of this study differ from previous research results in that they have also taken into account non-lethal cardiovascular events, thus filling a knowledge gap. They believe that the results may also be relevant to the formulation of a country’s family policy, as illustrated by the fact that China has recently abandoned the one-child policy and now allows up to three children per family.
– Since for various reasons involving selective abortions there has been an accumulation of boys in one-child families, they’ve become spoiled and often overweight, leading to public health problems. However, further research is needed to confirm the health effects linked to family size and both the biological and social roles related to placement in the sibling group.