A normal blood pressure reading is 120 over 80 or 120/80. The first number is the systolic pressure, which indicates the pressure on vessels when blood is moving through.

The second number is the diastolic pressure, which indicates the pressure between heartbeats.

In a 2013 study published in JAMA Neurology, Dutch scientists reported that patients with heart disease and lower than normal diastolic blood pressure showed a higher rate of brain atrophy (shrinkage) — a condition associated with dementia and Alzheimer’s disease.

The study included 663 patients with various forms of heart disease. Most of the volunteers were men, average age 57. Research volunteers with diastolic blood pressures lower than 70 showed more brain atrophy over time.

By contrast, patients with high blood pressure showed a decline in brain atrophy when blood pressure was treated.

The findings did not prove a cause-and-effect relationship between blood pressure and brain size, but they suggest that correcting hypertension may protect brain health, while decreasing normal blood pressure could pose brain health risks.