Having a sibling with a history of cardiovascular disease carries the same or greater risk as having a parent with a history of the disease, according to a new report from the long-standing Framingham Heart Study conducted by the National Heart, Lung, and Blood Institute (NHLBI), a part of the National Institutes of Health (NIH). Personal risk of having a cardiovascular event, such as a heart attack, stroke, or peripheral artery disease, may be raised by as much as 45% in middle-aged people whose brother or sister has had such an event.

The study appears in the December 28, 2005, edition of the Journal of the American Medical Association.

Even when data was adjusted for the fact that siblings may have similar lifestyle-related risk factors and may be of similar ages, the risk associated with having a sibling with cardiovascular disease remained high.

Physicians determine relative risk for cardiovascular disease by evaluating known risk factors: family history of heart disease, age, high blood pressure, high cholesterol, overweight, current or former smoking, physical inactivity, and diabetes. While having a parent or sibling with heart disease has long been suggested to increase risk, this study shows that having a sibling with heart disease is a significant risk factor independent of other measures.

"This study illustrates that even people who are not at high risk based on their own health status should talk to their doctors about the history of heart disease in their families, among siblings as well as parents, and ask what they can do to prevent a heart attack or stroke," said NHLBI Director Elizabeth G. Nabel, MD.

Researchers evaluated siblings from among 1188 men and 1287 women, all participants in the Framingham Heart Study. Participants were at least age 30 years at the time of a baseline examination, and were followed for 8 years for the occurrence of a cardiovascular disease event.

"We determined that one's risk from a sibling with a cardiovascular disease event remains elevated after taking into account age and other risk factors that may cluster within families. The risk may be even higher than the risk related to having a parent with cardiovascular disease," said Joanne Murabito, MD, ScM, of Boston University, the study's lead author. "The risk from a sibling with cardiovascular disease is significant even in persons with borderline elevated levels of total cholesterol, levels at which physicians are often undecided about medication treatment."

The Framingham Study is one of the first studies to take an independent, unbiased look at sibling risk. Unlike other studies of family history, which relied on often-unreliable participant recall, this study evaluated independent data from families within the 57-year-long observational study. Participants in this evaluation were from the study's Offspring group, the adult children of the original participants who first enrolled in the 1940s and 1950s.

"Our findings suggests that taking an accurate family history should be a crucial part of every physician's method of assessing heart disease risk, and should go beyond a simple 'yes' or 'no' question about the presence of disease in the family," said Dr. Murabito.

Patients should make the effort to collect medical history information from their siblings and parents and make sure to inform their siblings if they have a cardiovascular disease event such as a heart attack or stroke, she added.

"We believe that the reasons behind the strong association of risk between siblings are environmental as well as genetic. In addition to sharing the same genetic makeup, siblings may share similar dietary habits and physical activity patterns in their early years while living in the same household. These habits may continue on into adulthood when genetic factors begin to manifest," Christopher O'Donnell, MD, MPH, associate director of NHLBI's Framingham Heart Study and the study senior author.

"While you can't control your family history, there are many things you can do to control your risk for heart disease, including keeping your blood pressure, cholesterol and blood sugar under control, maintaining a healthy weight, avoiding smoking, and getting regular physical activity," said O'Donnell.

In May of 2004, the Framingham Heart Study research team demonstrated that having a parent with a cardiovascular disease history doubles personal risk of the disease.

National Institutes of Health News Release