Disturbing dreams and dementia risk across diverse populations

While the relationship between bad dreams, nightmares, and brain health is a relatively new area of research, the evidence to date has been remarkably consistent. Across a range of studies, including both cross-sectional and longitudinal designs, the emerging pattern is clear: more frequent disturbing dreams (bad dreams or nightmares) are linked with poorer cognitive performance and a higher risk of developing neurodegenerative diseases in later life, including all-cause dementia and Parkinson's disease.1, 2 However, despite the universality of disturbing dreams, most research thus far has been conducted in predominantly White, North American populations, leaving important questions about the generalizability of the disturbing dream-brain health relationship. In this context, the recent article by Lipnicki et al.3 in this issue, makes an important contribution. The authors examined the relationship between disturbing dreams and subsequent dementia risk using an impressive longitudinal, multi-cohort, population-based design, with 10,238 participants aged 60 to 89 from six countries, with a mean follow-up of 6.5 years. Participants were drawn from cohorts across three regions, including Asia (China, South Korea, and Taiwan), South America (Brazil), and Europe (Italy and France). This directly addresses previous concerns about generalizability. Another notable strength of the study is the inclusion of Alzheimer's disease (AD) as a specific outcome, alongside all-cause dementia. This enabled the authors to test whether the relationship between disturbing dreams and dementia risk extends to AD, rather than being limited to Lewy body dementia (LBD), a possibility that had previously been hypothesized but not formally examined.1 Lipnicki et al. found that frequent disturbing dreams, defined as occurring at least weekly, were associated with a higher risk of all-cause dementia during follow-up in the total sample. In sex-specific analyses, having any disturbing dreams was associated with an increased risk of AD in men, but not in women. Notably, this pattern, whereby disturbing dreams were more strongly associated with dementia risk in men than in women, is consistent with prior findings from North American cohorts.1 Why such a sex-difference might exist, however, is still unclear and warrants further investigation in future studies. The main novelty in these results, however, is the finding that disturbing dreams may be associated with incident AD. This is noteworthy given that many researchers are aware of a link between abnormal dream experience and LBD, but a relationship between dream phenomenology and AD has received relatively little attention. These initial findings suggest that characterizing the relationship between AD and dreaming may be a worthwhile area for future research. However, an important caveat in interpreting the findings of the study is the heterogeneity of the dataset. Some of the included cohorts used different items to measure disturbing dream frequency, different criteria for classifying incident dementia, and most notably, different cohorts contributed to the analyses of AD. As a result, it remains uncertain whether some of the sex- and disease-specific findings were influenced by imperfect harmonization across cohorts. Therefore, replication of these findings in cohorts with harmonized measures of disturbing dreams, and consistent methods for dementia classification and subtyping, will be essential to confirm the robustness of these sex- and disease-specific patterns. Overall, the report by Lipnicki et al. is an important contribution that extends our understanding of the link between disturbing dreams and dementia risk. Given that disturbing dreams are highly prevalent, easy to identify, and potentially modifiable, further confirmation of these results could have practical implications for global dementia screening and prevention, as well as for the broader promotion of brain health. A I Otaiku is funded by an Association of British Neurologists/Guarantors of Brain Clinical Research Fellowship. A I Otaiku is also supported by the UK Dementia Research Institute (UKDRI) Care Research and Technology Centre (CR&T). The author has no conflicts of interest to declare.