Sharing with siblings (if we’ve got them) is a love-it-or-hate-it fact of life.

But here’s something that we’d never want to share with them—an elevated stroke risk.

That’s a reality, though, according to a new study, which shows that your odds of suffering an ischemic stroke (the most common type, caused by a blood clot in the brain) dramatically increase if your brother or sister has one—especially if he or she has one before age 55.

It’s not a total surprise, of course, that having immediate family members with certain diseases raises your risk for the same diseases.

But I think you’ll be surprised to see just how much having a sibling who had a stroke raises your risk…

ODDS THAT NOBODY LIKES

Researchers found that when a person had a sibling who had a stroke, his personal risk for stroke went up 64%, compared with a person who had a sibling who did not have a stroke…and for a person with a half-sibling who had a stroke, his risk was 41% higher. For those whose brother or sister suffered a stroke at age 55 or younger, the odds were even more worrisome—these folks had an almost doubled risk of experiencing strokes themselves at around the same age. The gender of either sibling did not influence these sibling risk percentages.

To put these bumped-up risk numbers in perspective, they are about the same as what would be expected if someone’s mother or father had a stroke, said lead author Erik Ingelsson, MD, PhD, a professor of cardiovascular epidemiology at the Karolinska Institute in Sweden.

Why is this important? Because it shows that when someone has a stroke, that person’s siblings must not consider it just an individualized event—instead, it is a strong signal for higher stroke risk in all the family’s siblings…and that’s so even if there’s no history of stroke in the parents!

PROTECT YOURSELF

Unfortunately, researchers weren’t able to tell from the medical records they studied what other hereditary factors—such as high cholesterol or high blood pressure—may have played a role in the sibling stroke link. Dr. Ingelsson told me that the heightened risk is likely to be a combination of genetic and environmental/lifestyle risk factors. In other words, some shared family traditions (such as eating fattening meals, smoking or not being physically active) could have as much to do with our overall stroke risk as any inherited predisposition.

We can’t change whatever genetic hand we’ve been dealt…but, as Dr. Ingelsson noted, there’s a lot we can control. It’s firmly within our power to reduce our stroke risk by eating heart-healthy foods (such as fruits and vegetables, low-fat meats and fish), exercising, avoiding smoking, and keeping blood pressure in a healthy range. In fact, if one of your siblings has had a stroke and you want there to be some kind of silver lining, you can treat it as a clear warning to you: Get with it. You know what to do!