Women with high blood pressure in their 40s are at increased risk for dementia in later years, researchers report. But the finding does not hold for men.

Beginning in 1964, investigators collected health and lifestyle information on 5,646 men and women when they were 30 to 35 years old, and again when they were in their 40s. From 1996 to 2015, 532 of them were found to have Alzheimer’s or other forms of dementia. The study is in Neurology.

Hypertension in women in their 30s was not associated with dementia. But women who were hypertensive at an average age of 44 had a 68 percent higher risk for dementia than those who had normal blood pressure at that age, even after adjusting for B.M.I., smoking and other risk factors.

High blood pressure in men in their 30s or 40s was not associated with later dementia, but the study’s senior author, Rachel A. Whitmer, said that studies have tied hypertension in men in their 50s to later dementia. Dr. Whitmer, a senior research scientist at Kaiser Permanente in Oakland, Calif., added that hypertension is more common in men, and the hypertensive men in the study tended to die at a younger age than the women.

“The big picture here is that brain health is a lifelong issue,” she said. “What you do in young adulthood matters for your brain in old age.”