For patients with high blood pressure who hope to ward off dementia, doctors have the same advice for those looking to protect their hearts: Go lower.

In a comprehensive new study, researchers found that driving down patients’ systolic blood pressure readings to a new lower target level reduced their risk of developing mild cognitive impairment, or MCI, by close to 20 percent. MCI is a decline in memory and thinking skills that is slight but noticeable, and it affects between 15 percent and 20 percent of people over 65. For as many as half of those diagnosed with MCI, a diagnosis of dementia will come later.

The new research found that compared to subjects whose blood pressure control regimen was more relaxed, subjects whose blood pressure was more strictly controlled were 15 percent less likely to be diagnosed with mild cognitive impairment and subsequent dementia.

The new findings come a year after the American Heart Association and the American College of Cardiology adopted a new target for those with hypertension. Physicians groups had long considered blood pressure readings of 140/90 mmHG to be an acceptable target for those with hypertension, but in 2017, they urged physicians to get their patients with high blood pressure to 130/80.

The new research suggests that there are powerful benefits to getting the first number in that reading — systolic blood pressure — to an even lower target: 120 mmHG.

Systolic blood pressure is the amount of pressure in a person’s arteries during the contraction of the heart muscle. Because it is the highest pressure to which the blood vessels are subjected, systolic blood pressure is thought to have the most detrimental impact on the delicate capillaries that nourish the brain as well as the kidneys, heart and liver. In large populations, lowering that reading to 120 has been found to reduce rates of cardiovascular disease and kidney failure.

Dr. Lon Schneider, an Alzheimer’s specialist, suggested that the average age of the trial’s subjects — 68 — may obscure an important point: that strict blood pressure control will likely prevent dementia most effectively if it starts early and is followed through midlife.