For better or worse, your parents’ health history can predict your own: If your mom or dad has a serious condition like obesity, heart disease or cancer, your own risk is, of course, higher.

But how much higher? The truth is, what it means to have a family history can vary a lot depending on the disease. That’s why it’s important to not only know your medical background, but also to tease out how much hereditary factors influence your individual risk so you can identify the precautions to take to protect yourself while you’re still healthy.

“Knowing your family history might save your life,” says Theresa Frezzo, M.S., a genetic counselor and research coordinator at the Center for Genetic Medicine at Northwestern University in Chicago. “If you know that you have a family history of a particular disease, you can report that information to your health-care provider and take steps to modify your risk. With most adult-onset illnesses, your heritage is not your destiny. There are preventive measures you can take that can reduce your risk of following in your family member’s footsteps.”

But it’s up to you to be proactive about your health care: A recent study led by Frezzo found that approximately 20 percent of patients in an internal-medicine clinic were at increased risk for diseases with genetic links–though this was not noted in their charts. (These family histories came to light because either the patients were asked for the information in a separate questionnaire or they were interviewed by a genetic-counseling intern.)