Relative risk: Having lots of siblings has been linked to heart disease
You can choose your friends but not your family, as the saying goes.
While smoking, failing to exercise and eating poorly have long been linked to a range of diseases, the onset of cardiovascular conditions may also be a "family affair".
Having relatives with heart disease is known to raise an individual's risk, however, the effect of siblings was less clear.
To learn more, scientists from Lund University in Malmö analysed over 2 million people who were born in Sweden between 1932 and 1960.
Results, published in the journal BMJ Open, reveal those who had lots of brothers and sisters were more likely to develop heart disease over the next 25 years.
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On the other hand, being an only child was linked to a lower risk of premature death.
Although it is unclear why these outcomes may occur, the scientists believe their results could be "of public health interest".
The health effects of so-called "sibling ranks" is somewhat muddled, with past research linking having brothers and sisters to both improved and deteriorated wellbeing.
To learn more, the Lund scientists analysed 1.36 million men and 1.32 million women – aged 30 to 58 – from Sweden's Multiple-Generation Register.
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Over 25 years, the men with one or two siblings were less likely to have endured a "cardiovascular event" – like a heart attack – than those who were an only child.
The men with four or more siblings, however, faced a higher cardiovascular risk.
Those with three or more siblings were also more likely to have endured a coronary event. This is generally defined as the narrowing of the coronary arteries due to a build-up of plaque, triggering complications.
When it came to deaths, however, the men with more than one sibling were less likely to have died over the study's follow-up period than those with no brothers or sisters.
Among the female participants, those with at least three siblings were more likely to have endured a cardiovascular event than their only-child counterparts.
Coronary events were more also common among the women with two or more siblings.
The women with at least one brother or sister were less likely to have died during the follow-up period, however.
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The scientists have stressed their study was observational, and therefore does not prove cause and effect.
They were also unable to collect information on the participants' weight, diet or smoking status. Other factors were accounted for, however, like their socioeconomic status and the presence of certain diseases, such as diabetes.
"More research is needed to understand the links between sibling number and rank with health outcomes," wrote the scientists.
"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."
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