A long-term study released in early 2018 found a "strong link" between hearing loss and dementia in older adults. A third of participants who had hearing loss were found to be more likely to have other major health issues such as depression, disability, and dementia. Similarly, a 2011 John Hopkins School of Medicine study found that participants who had mild to severe hearing loss were more likely to develop dementia. "When you have hearing loss your brain has to work hard to compensate for the lack of auditory input," Dr. Lawal says. "When this continues for many years and people don’t get help for their hearing loss, the brain can weaken which increases the likelihood of developing dementia."

Recent research published in the journal Frontiers in Aging Neuroscience found links between herpes simplex virus type 1 (HSV-1), which often causes mouth sores, and Alzheimer’s disease. Researchers looked at data of over 8,000 adults over the age of 50 who had herpes and compared them with over 25,000 people who did not. As researchers found, those with the herpes virus were 2.5 times more likely to develop dementia than those who did not. Researchers also discovered that people infected with HSV-1 carry a specific gene associated with Alzheimer’s disease, ApoE4. This gene is known to increase the risk for getting the disease.

A 2018 study published in the journal Sleep found links between sleep disturbances and Alzheimer’s disease. Researchers conducted a survey of 124 men and women on their "daytime sleepiness levels" and napping habits and compared their responses with PET and MRI scans they took about 16 years later. Feeling excessively sleepy during the day is a common symptom of several sleep disorders like insomnia or sleep apnea. According to the study, people who said they often felt sleep during the day were about three times more likely to show signs of Alzheimer's disease in the brain. Although researchers can't say for sure that sleep disorders cause Alzheimer's disease, there is a link there that's worth exploring for future studies.

In a 2018 study published in the journal Diabetologia, researchers observed over 5,100 adults over 10 years. People who had higher blood sugar levels had faster rates of cognitive decline than those with more normal levels. According to the Alzheimer Society, dementia is sort of like a type of diabetes of the brain. The brains of people with both diabetes and dementia are similar in the way that glucose is not properly used in the brain. When this happens, it can reduce the brain's ability to function as it should.

A 2017 study from the University of Southern California found links between air pollution and dementia in older women. They discovered that tiny air pollution particles, that mostly come from power plants and cars, can get inside the body through the nose and then travel into the brain. Breathing in toxins can increase inflammation in the body. If someone were to have the Alzheimer's gene, too much exposure over time to those toxic particles can "exacerbate and promote" the disease. According to researchers, the adverse affects were found to be much stronger in older women who had the gene. More research still needs to be done to confirm that air pollution really does cause dementia. But if it does, researchers say air pollution could possibly be the cause for over 20 percent of dementia cases.

A 2016 study published in the journal Annals of Neurology, found a link between a person's sense of smell and Alzheimer’s disease. As researchers found, participants who were unable to correctly identify certain odors such as menthol, strawberry, and lemon were the ones at risk for having the disease. This led researchers to believe that one's poor sense of smell can possibly be an early indicator of Alzheimer's disease.

A 2018 study published in the Journal of Gerontology: Psychological Sciences analyzed data of over 12,000 people over 10 years. As researchers found, people who reported to having greater feelings of loneliness were 40 percent more likely to get dementia. Although there's not just one clear explanation as to why, researchers say some people may cope with feelings of loneliness by engaging in behaviors that can damage the brain like binge drinking of being sedentary.

Just to be clear, these studies show possible links to dementia. It doesn't necessarily mean these things can cause it.

The possibility of getting dementia may seem far off in the future, and some factors that contribute to it may be out of your control. But as Dr. Lawal says, there are things you can do right now to limit your risk. "Don't smoke, protect yourself against concussions when participating in high-impact activities, don't over-consume alcohol, stay active, and eat a balanced diet," he says. So just do your best to live a healthy lifestyle as much as you can.