Having a brother or sister with cardiovascular disease (CVD) is bad news for your own odds of developing problems, research has found.
Heart disease may run in the family
Using data on 5,000 people, scientists have calculated that middle-aged adults who have a sibling with CVD have a 45% increased risk of the same condition.
The risk is even higher than that linked to having parents with CVD.
The study, by the US Framingham Heart Study team, features in the Journal of the American Medical Association.
It is known that having a family history of CVD is linked to an increased risk of the condition.
However, the Framingham team say there has previously been a lack of definitive research into exactly how much having a brother or sister with the condition ups the ante.
Those studies that have been done have produced widely differing conclusions.
The US researchers analysed data on more than 5,000 people from a major project on heart disease which began in 1948.
Writing in JAMA, they said: "Sibling CVD should be considered as important as parental premature CVD in the assessment of risk."
They said further investigation was needed to better understand why sibling history of CVD should be such a strong predictor of problems.
They postulate that an early shared environment may be a factor with people developing poor eating or exercise habits in childhood which they carry through into their adult lives.
Belinda Linden, head of Medical Information at the British Heart Foundation, said: "This study reinforces the evidence that although the genes we inherit from our parents can influence our risk of heart disease, the interaction between our genes and our lifestyle is probably more influential than our genes alone.
"The results highlight how important our lifestyle is, even as we grow up, in determining long term risk of heart disease.
"The good news is that whilst we can't change our genes, most people can take simple lifestyle steps to reduce the risk of heart disease for themselves and their families."