Despite massive research efforts, there is still no diagnostic test for Alzheimer’s disease. However, recent studies have uncovered three surprising early warning signs of the brain illness.

No. 1: Weak handshake. Scientists at the Population Health Research Institute in Hamilton, Ontario, found that poor hand grip is predictive of dementia, heart problems, and stroke.

Researchers looked at 140,000 people from 17 different countries and found a clear and consistent link between weak grip strength and death from any cause, including Alzheimer’s.

“This study really strengthens the case for using grip strength as a marker for health problems,” says Bob McLean, of Harvard Medical School’s Institute for Aging Research.

In fact, the American Academy of Neurology reports that people with firm handshakes are 42 percent less likely to suffer from dementia or stroke.

Researchers theorize that cardiovascular weakness causes weakness in the extremities, which is evident during a handshake. The same weakness can reduce cognitive functioning, they believe.

No. 2: Slow walking gait. Researchers at Boston Medical Center found that middle-aged people with slower walking speeds were 1.5 times more likely to develop dementia.

That’s because walking speed indicates general fitness, Kevin Campbell, M.D., a leading North Carolina cardiologist, tells Newsmax Health.

“Physical activity is important to lowering risk of dementia,” he notes. “Those who engage both physically and socially, as in the case of walking, lower their risk of these dangerous conditions.”

No. 3: Poor sleep. The brain uses sleep to flush out toxins that play a role in Alzheimer’s disease, according to a study at the Washington University School of Medicine.

“Sleep provides the time to recharge and reset your body and that obviously includes the brain,” says Dr. Campbell. “It also allows you to repair the connections between brain cells which may help explain the link between a lack of sleep and Alzheimer’s disease.

“Sleep is a very ordered function. It moves from cycles of light to deeper sleep, where we get the most rest and brain repair. If you have interrupted sleep or wake often, you may never get to the deeper sleep stages and your brain will suffer.”