By Abidemi Otaiku NIHR Academic Clinical Fellow in Neurology, University of Birmingham We spend a third of our lives sleeping. And a quarter of the time we sleep is spent dreaming. So for someone with a life expectancy of about 73 years, that’s a little over six years of sleep. However, considering the central role sleep plays in our lives, we still know very little about why we dream, how the brain creates dreams, and most importantly, how important our dreams can be to our health. Especially the health of our brain. My latest study, published in The Lancet’s eClinicalMedicine, shows that dreams can reveal a surprising amount of information about the health of our brains. More specifically, it suggests that having bad dreams and frequent nightmares (bad dreams that make you wake up) during middle or late age may be linked to an increased risk of developing dementia. In the study, I analyzed data from three large US studies on health and aging. They involved more than 600 people between the ages of 35 and 64, and 2,600 people aged 79 and over. All participants were free of dementia at the start of the study and were followed for a median of nine years for the middle-aged group and five years for the older participants. Weekly Nightmares At the beginning of the study (2002-2012), participants completed a series of questionnaires, including one that asked about how often they experienced bad dreams and nightmares. I analyzed the data to find out if participants with higher frequency of nightmares at the beginning of the study were more likely to experience cognitive decline (a rapid decline in memory and thinking skills over time) and be diagnosed with dementia. I found that middle-aged participants who experienced nightmares every week were four times more likely to experience cognitive decline (a precursor to dementia) over the next decade. For their part, older participants were twice as likely to be diagnosed with dementia. Interestingly, the connection between nightmares and future dementia was much stronger for men than for women. For example, older men who had nightmares every week were five times more likely to develop dementia compared to older men who did not have nightmares. In women, however, the increased risk was only 41%. A very similar pattern was found in the middle-aged group. Symptom or cause of dementia? Overall, these results suggest that frequent nightmares may be one of the first signs of dementia, which may precede the development of problems with memory and thinking skills by several years or even decades, especially in men. On the other hand, it is not unreasonable to suspect that having bad dreams and nightmares on a regular basis is even a cause of dementia. Given the nature of this study, it is not possible to be sure which of these theories is correct (although I suspect it is the former). Regardless of which theory turns out to be true, however, the main implication of the study remains the same, namely that having regular bad dreams and nightmares during middle and late life may be somehow associated with an increased risk of develop dementia as you age. Recurring nightmares can be treated The good news is that recurring nightmares are treatable. And first-line medical treatment for nightmares has already been shown to decrease the buildup of abnormal proteins associated with Alzheimer’s disease. There have also been case reports showing improvements in memory and thinking skills after treating nightmares. These findings suggest that treating nightmares could help slow cognitive decline and prevent the development of dementia in some people. This will be an important avenue to explore in future research. The next steps in my research will include studying whether nightmares in young people may also be linked to an increased risk of dementia. This could help determine if the nightmares are the cause of dementia or if they are simply an early sign in some people. I also plan to investigate whether other characteristics of dreams, such as the frequency with which we remember them and their intensity, can help determine the likelihood that people will develop dementia in the future. This research could not only help clarify the relationship between dementia and sleep, and provide new opportunities for earlier diagnoses – and possibly earlier interventions. It could also shed new light on the nature and function of the mysterious phenomenon we call sleep.