Researchers conducting the study said the findings could be due to the fact that blood pressure-lowering drugs like beta blockers and potassium-sparing diuretics result in higher potassium levels in the body.
The researchers looked at the link between anti-hypertensive drugs and the incidence of Alzheimer's in 3,297 elderly residents of Cache County, Utah.
In the study -- done from 1995 to 1997 -- participants were interviewed for medications they were taking and were screened for dementia.
Those already showing signs of Alzheimer's in the initial interview were excluded from the study.
The interviews revealed that 1,507 of the patients used antihypertensive medications and 1,790 did not.
During follow-up three years later, 104 participants had developed Alzheimer's, but the patients who were using the blood pressure-lowering drugs at the study's outset "were significantly less likely to have developed (Alzheimer's) than those who were not," the scientists reported.
Diuretic drugs showed a more than 70 percent reduction in the risk of the brain disease, while beta blockers and anti-hypertensive medicines known as dihydropyridine agents also seemed to have a protective effect.
On the other hand, ACE inhibitor drugs did not appear to be linked to a decreased Alzheimer's risk.
Researchers found these results were not affected after controlling for other factors such as gender, age, high cholesterol, diabetes and genetic risk.
"We suggest these findings should prompt further epidemiologic and basic science studies into the possible neuroprotective effects of these drugs," the researchers said.