If you or a loved one kicks, talks, or strikes a partner during sleep, it may signal dementia risk years before memory problems emerge. A specific sleep disorder called REM sleep behavior disorder (RBD) is now recognized as one of the earliest warning signs of neurodegenerative disease, sometimes appearing a decade before diagnosis.

What Is REM Sleep Behavior Disorder and Why Does It Matter?

During normal dreaming, the brainstem temporarily paralyzes your muscles so you don't act out your dreams. In RBD, this protective mechanism breaks down. The brainstem structures that control this paralysis begin to degenerate, causing people to physically act out their dreams instead of remaining still.

The critical insight: this degeneration doesn't happen at the same time as other dementia symptoms. It starts years earlier. A meta-analysis of RBD patients found that 33.5% developed a neurodegenerative disease within five years, rising to 82.4% at ten years, and 96.6% at fourteen years. Roughly 90% of people with RBD will eventually develop one of two conditions: Parkinson's disease, accounting for 43% of cases, or Lewy body dementia at 25%.

Researchers at Université de Montréal, led by neuropsychologist Shady Rahayel, published work in 2025 confirming that scientists can now predict, years ahead, which RBD patients will develop Parkinson's or Lewy body dementia. This represents a major shift in how doctors think about early detection.

What Other Physical Warning Signs Should You Watch For?

RBD isn't the only early indicator. Experts have identified several physical markers that appear before cognitive decline becomes noticeable. These signs are often overlooked because they seem unrelated to brain health, yet they reflect underlying neurological changes.

• Balance Problems: Failing to stand on one leg for ten seconds before age 70 is a significant marker. A study of 686 Alzheimer's patients showed that those who failed this test experienced notably faster cognitive decline over two years than those who passed.
• Weakened Grip Strength: This measure tracks how effectively the brain communicates with the body to control sensation and movement. A UK Biobank study of over 190,000 adults found that lower handgrip strength directly correlates with dementia diagnoses, fluid intelligence, and prospective memory, with the strongest link to vascular dementia.
• Difficulty Rising From a Chair: Struggling to complete a bodyweight squat or rise from a seated position can signal early neuromuscular decline, reflecting the brain's weakening ability to coordinate complex, large muscle movements.
• Social Withdrawal: Isolation isn't just a result of cognitive decline; it may be a driver. Research indicates that social isolation and loneliness increase dementia risk by 26% and 32% respectively.

How Can You Distinguish Normal Aging From Early Cognitive Decline?

Everyone forgets things occasionally. The key question is whether memory changes cross the line from ordinary to concerning. Normal aging involves gradual brain tissue shrinkage, but Alzheimer's shows dramatic changes in specific regions like the temporal lobe and hippocampus, the structure deeply involved in forming new memories.

Three main warning signs should prompt a cognitive evaluation, according to Dr. Barak Gaster, cognition in primary care director at the University of Washington: losing short-term memory such as asking the same question repeatedly within a short time; having difficulty completing complex tasks like following a recipe; and becoming disoriented in familiar places, such as getting lost on a route you've taken many times.

Dr. Barak Gaster

"[There are] three main warning signs for primary care providers. These are: losing short-term memory, such as asking the same question repeatedly within a short time; having difficulty completing complex tasks, like following a recipe; and becoming disoriented in familiar places, such as getting lost on a route you've taken many times. If these signs are present, they should prompt a cognitive evaluation," said Dr. Barak Gaster.

Dr. Barak Gaster, Cognition in Primary Care Director at the University of Washington

Beyond these core signs, other red flags include frequent confusion about time or place, difficulty following conversations, repeating the same questions, and noticeable changes in mood, personality, or judgment. When loved ones begin expressing concern about changes they've noticed, that too is an important signal.

What Often Gets Missed: The Overlooked Early Signs

Some of the earliest warning signs for dementia risk are frequently overlooked or mistaken for other conditions. These include changes or loss of smell, sleep issues and daytime sleepiness, increased agitation, depression, social withdrawal, and lack of motivation.

Real-world examples illustrate how these signs show up in daily life. LuPita Gutierrez Parker, eventually diagnosed with early-onset Alzheimer's disease, first noticed problems while working as a university recruiter. She started forgetting appointments, losing track of notes, and struggling with data entry that had previously been routine. During presentations she'd given many times before, she would lose her place and have difficulty searching for words. Myra Garcia had a similar experience, beginning to have trouble with numbers and remembering colleagues' names while working at the University of La Verne.

How to Protect Your Brain and Reduce Dementia Risk

• Regular Physical Activity: Exercise improves blood flow to the brain and has been associated with slower rates of cognitive decline in multiple studies. Getting vaccinated for conditions like shingles, the flu, and tuberculosis has also been demonstrated to diminish dementia risk.
• Mediterranean Diet: A nutrient-rich diet emphasizing vegetables, fish, olive oil, and omega-3 fatty acids is associated with better brain health as people age.
• Quality Sleep: During deep sleep, the brain clears out harmful proteins, including beta-amyloid, the substance that builds up in the brains of people with Alzheimer's disease. Prioritizing 7 to 8 hours of sleep nightly may be one of the most underappreciated strategies for long-term brain health.
• Social Engagement: Research consistently shows that isolation and loneliness are linked to higher dementia risk. Staying connected with friends, family, and community may help protect the brain in ways scientists are still working to quantify.
• Cognitive Challenges: Challenging the brain with new learning, whether through reading, puzzles, learning a new skill, or engaging with music, may help build cognitive reserve, a kind of resilience that helps the brain compensate for age-related changes.
• Blood Pressure Management: Maintaining healthy blood pressure reduces dementia risk, as conditions like high blood pressure, diabetes, and high cholesterol put the brain in a more vulnerable state.

The window for intervention is wider than most people realize. Most people wait for memory loss to seek help, but research suggests the real opportunity opens years earlier. For many, a restless night's sleep may be the brain's first distress signal.

If memory issues are beginning to affect you or a loved one's daily life, experts say it's important not to wait. Keeping a journal of symptoms can help you track patterns and provide useful information for a doctor. Noting when memory lapses happen, how often, and whether they're getting worse over time gives clinicians concrete data to work with.