Researchers from the University of Exeter in the UK tracked the blood pressure and health outcomes of 230 people for 10 years. A difference in systolic BP of 10mmHg between arms was shown to indicate a diminished blood flow to the legs and feet. Raise the difference to 15mmHg, and you’re looking at a sign that the blood flow to your brain may be insufficient—a condition that can cause dementia and heart problems.   The difference in BP readings is caused by the narrowing or hardening of an artery on one side of the body, explains study author Christopher Clark, MD, of the Peninsula College of Medicine and Dentistry at the University of Exeter. “This narrowing is due to early arterial disease, and therefore the detection of an inter-arm difference is a significant warning sign,” Clark says. And finding a difference between arms isn’t uncommon. Dr. Clark’s team found 24 percent of the study participants had at least a 10mmHg disparity in blood pressure readings. So what does this mean for you? If you’re 40 or older, ask your doctor to check your blood pressure in both arms at least once a year—more if you’re at increased risk for heart disease, advices Dr. Clark. It may also be a good idea to purchase a blood pressure monitor for your home and check both of your arms once every six months.    If you or your doctor finds a discrepancy, don’t freak out. Dr. Clark says different BP readings are a sign of increased risk, not an urgent threat. Also, one reading could be the exception, not the rule. A series of readings over a week is the only way to tell whether the BP difference is a warning sign or an anomaly. Also see: Study Links BPA to Heart Disease, How Love Benefits Your Blood Pressure, The Surprising Heart Attack Risk