More than 5 million Americans have Alzheimer's disease. While many of us are familiar with the common symptoms, such as memory loss, other potential early warning signs of the disease may surprise you.

Knowing what they are could help you help a loved one — or even yourself.

Here are some signs the Alzheimer’s Association and dementia researchers say are worth paying attention to. Each of these may be related to something other than Alzheimer’s disease, cautions Ruth Drew, MS, director of family and information services for the Alzheimer's Association: Some might stem from another neurological issue that's readily treatable. The important thing is not to ignore these signals, she says, but to get your loved one evaluated by a doctor.

Related: How to Prevent Dementia Patients from Wandering

Laughing inappropriately

Suppose you're telling your husband about a distressing event at work, or about an almost-collision you had on the road. You expect empathy and perhaps a hug, but you get laughter instead. Drew says this may be an early sign of Alzheimer’s. She has heard many stories about inappropriate mirth and other odd responses in people who were later diagnosed with the disease.

People with Alzheimer's sometimes ''lose some of their normal inhibitions," Drew says. "They might act in ways that might come across as inappropriate or rude.”

A distinct change in one’s sense of humor was confirmed as a possible sign of dementia by a study published in the Journal of Alzheimer’s Disease. Researchers from University College London recruited 48 patients with frontotemporal dementia and asked their friends and families which kind of comedy the patient preferred. Most of the patients preferred slapstick to satire, according to friends and family, who also recounted how their loved one's sense of humor had changed — often bizarrely — before they were diagnosed with dementia. As an example, the authors said, one man laughed when his wife scalded herself badly.

Loss of smell

Several studies suggest that losing the sense of smell may signal mental decline. In November 2015, a study published in JAMA Neurology found that older adults who had the poorest scores on smell tests were 2.2 times more likely to start having mild problems with their memory. If they already had memory problems, they were more likely to develop Alzheimer’s disease, according to Rosebud Roberts, MB, the lead researcher and a professor of neurology at the Mayo Clinic in Rochester, Minnesota.

In Alzheimer's, the first cranial nerve — the olfactory nerve, which governs smell — is typically one of the first nerves to be affected. But the JAMA authors cautioned their study did not prove a cause-and-effect relationship.

Frequent falls

While older adults are more prone to falls than younger adults in general, falls may also be an early warning sign of Alzheimer's, according to researchers from Washington University in St. Louis. They followed 125 adults age 65 and older for a year, asking them to track any falls. When the researchers looked at the brain scans of the frequent fallers, they found a link between those with early Alzheimer's disease and those who fell more often.

In their study, published in a 2013 issue of Neurology, the researchers speculate systemic changes in the body, unrelated to changes in the brain, may occur in Alzheimer’s before the brain is affected.

Related: Bringing Mom Home: How to Create a Safe Space for Your Loved One with Alzheimer's

A change in eating habits

In early Alzheimer's, including cases not yet diagnosed, a person may eat constantly — or hardly at all. "I've seen it go both ways," Drew says. "One woman forgot she had just eaten after a meal, and she would say she hadn't had anything to eat."

"I also know of people who no longer register they are hungry. They don't feel hungry and they don't remember to eat” — something that’s potentially dangerous, she adds.

Staring or zoning out

Apathy can often be a sign the brain isn't processing information normally, says Drew. The brother of a man later diagnosed with Alzheimer’s found that his sibling would turn on a favorite TV show, then simply stare into space. That was likely an early sign that "this is a brain that has been attacked" by Alzheimer’s, according to Drew.

Related: 4 Ways to Reduce Your Risk of Alzheimer's Disease

Disrupted sleep

Drew says she has heard many reports of disrupted sleep in people later diagnosed with Alzheimer’s. One of the families she helped told her a man who ended up developing the disease began getting up at 2 a.m. "He would insist it was daytime, wake up the house and insist it was time to get going," she says.

That behavior, she says, likely originated from the disorientation with space and time that many people with Alzheimer’s experience.

Related: An Anti-Alzheimer's Diet?

Kathleen Doheny is a Los Angeles journalist specializing in health, behavior and fitness topics.