Study Finds That Nightmares May Predict A Real-Life Illness

Despite a wealth of studies and decades of research, there is no consensus on why we dream (or how to interpret dreams with numbers, for that matter). While we do understand basic things like how much sleep human beings need in order to function, there are multiple theories as to the significance of dreams and why they happen. Some researchers see dreams as the result of chemical changes in the brain which occur during sleep — a byproduct of REM sleep which serves no major purpose. Other theories present evolutionary explanations, whereby dreams are seen as a way for human beings to walk through scenarios in a sort of rehearsal for real-life. Alternative explanations posit that dreaming is essentially the biological equivalent of defragging your hard drive, with the brain attempting to make sense of the information it has absorbed throughout waking hours, or process traumatic memories. 

But while all of these theories are fascinating, nothing has been proven. Perhaps even more intriguing are nightmares. According to the Sleep Foundation, nightmares are "vivid dreams that may be threatening, upsetting, bizarre, or otherwise bothersome." Crucially, though, within sleep medicine, nightmares are classified as different from mere bad dreams in the sense that nightmares actually cause people to wake up from sleep.

As with dreams overall, there is no accepted consensus about nightmares, but we do know that stress and anxiety, mental health conditions, sleep deprivation, and Post Traumatic Stress Disorder can provoke them. Now, research suggests these distressing dreams might be even more sinister for middle-aged and older adults, as they could very well be a predictor for cognitive decline and dementia later in life.

When we sleep, we go through several stages. Rapid Eye Movement (REM) sleep is the stage where vivid dreams take place and you experience brain activity closer to being awake than the deeper NREM stage of sleep. During REM sleep, our heart rate and blood pressure remain close to waking levels, and we experience an irregular heartbeat and higher respiration rates. It's during this stage that nightmares occur more frequently, which means that, due to the fact that we spend more time in REM sleep toward the second half of the night, we are more likely to experience nightmares during the same period.

Unlike night terrors, which occur during the deep sleep phase where delta waves become frequent, dreams and nightmares happen during a REM sleep cycle, meaning we're typically able to remember what our nightmares contained after we wake up.

While anybody can experience nightmares, children — especially those between 3 and 6 — are more frequently affected. Like with so many aspects of dreaming, it's not known conclusively why this is the case, though some theories posit that it is a manifestation of childrens' inherent vulnerability. But if you happen to experience frequent nightmares in middle or older age, your brain may be telling you something about your future health.

In the absence of a consensus on why we have nightmares, researchers continue to conduct studies on these distressing dreams in order to better understand them. One recent study revealed a startling correlation between nightmares and cognitive decline that suggests nightmares, far from simply spooking us in the middle of the night, can be a sign of — or indeed even a cause of — future mental decline.

The research, entitled "Distressing dreams, cognitive decline, and risk of dementia: A prospective study of three population-based cohorts" was published in The Lancet's eClinicalMedicine in 2022. Previous research in this area has shown that distressing dreams are associated with faster cognitive decline and increased dementia risk in people with Parkinson's disease. But this study aimed to look at whether the same held true for the general population. The researchers analyzed data from three large studies of health and aging, which comprised about 600 people aged 35 to 64, and 2,600 people aged 79 and older. In 2002, at the beginning of the study, all participants were dementia-free, and they were asked to fill out a questionnaire about how often they had bad dreams and nightmares. Middle-aged adults were then followed for an average of nine years while older participants were followed for five.

Dr. Abidemi Otaiku, a clinical research fellow at Imperial College London, analyzed the data at the end of the study to see whether those that reported a higher frequency of nightmares were more likely to have any decline in memory and thinking skills over time and be diagnosed with dementia. Indeed, the results suggested that middle-aged and older people who experience frequent bad dreams and nightmares may have an increased risk of this sort of cognitive decline.

Far from showing a tenuous link between nightmares and a decline in memory and thinking skills over time, the research showed that self-reported high frequency of distressing dreams among the middle and older age participants was significantly associated with cognitive decline later in life. According to the researchers, middle-aged adults who reported having distressing dreams on a weekly basis had a four-fold risk of experiencing cognitive decline compared to those reporting no distressing dreams. Older adults were twice as likely to develop dementia.

What's more, the link between nightmares and dementia in men was much stronger than it was for women. Writing about his research for Science Alert, Dr. Abidemi Otaiku noted that older men who had reported having nightmares every week had a five-times higher chance of developing dementia, whereas women only had a 41% increase in risk.

Not only did the study reveal this link between nightmares and cognitive issues later in life, it showed that dreams have a lot to tell us about brain health overall. As Dr. Otaiku put it, this research suggests that "frequent nightmares may be one of the earliest signs of dementia, which can precede the development of memory and thinking problems by several years or even decades — especially in men." Anothe — perhaps even more alarming — explanation for this link is that the nightmares are actually the cause of the future cognitive decline, though as Dr. Otaiku notes, there is no way to tell which explanation is accurate without further research.

The obvious implication of this research is that doctors might well be able to identify dementia much earlier than if they were relying on the onset of typical cognitive issues associated with the condition, such as memory loss. Using nightmares as a predictor of later cognitive decline could help treat dementia much earlier and more effectively in the future — though more research is needed to fully understand the connection between dreams and cognitive decline later in life.

What's more, if nightmares are indeed the cause of (and not simply an indicator of) later life cognitive issues, then treating individuals for nightmares early could potentially decrease rates of dementia. In order to discover more about the correlation between nightmares and developing dementia, Dr. Abidemi Otaiku intends to carry out more research to investigate whether nightmares in young people might also be linked to increased dementia risk. He also plans to investigate whether our dreams generally could reveal more about our risk for cognitive decline later in life, including conducting research into how often individuals remember their dreams and how vivid they are.

As the doctor wrote in his ScienceAlert piece, "The research might not only help to shed light on the relationship between dementia and dreaming, and provide new opportunities for earlier diagnoses — and possibly earlier interventions — but it may also shed new light on the nature and function of the mysterious phenomenon that we call dreaming."