UK: Those children experiencing bad dreams at 11 years of age are two times more likely to develop cognitive impairment and seven times more likely to develop Parkinson's disease by the age of 50 years. The role of genetics is also crucial here because one gene which increases the risk of nightmares is tied to the risk of Alzheimer's disease in old age. So the role of genetics is also implicated in this context.

Research says that those experiencing Distressing dreams in middle-aged and older adults have the risk of developing cognitive impairments like dementia and PD. There needs to be more data related to young people developing these conditions due to distressing dreams.
The study is published in The Lancet.
The research in this longitudinal analysis used data from the 1958 British Birth Cohort Study.
The children's mother gave information about distressing dreams at ages 7 (1965) and 11 (1969). The cognitive assessment, doctor-diagnosis, and multivariable Firth logistic regression determined cognitive impairment and PD at the age of 50.
The study's findings include the following points:
The follow-up was available for 6991 children constituting 50.6% female.
At age 50, 267 individuals, constituting 3.8%, developed cognitive impairment/PD.
Regular distressing dreams during childhood were significantly associated with a higher risk of cognitive impairment or PD by age 50.
Children who had persistent distressing dreams (2-time points) had an 85% increased risk of developing cognitive impairment or PD by age 50, with an adjusted odds ratio of 1.85 compared to children who never had distressing dreams.
Concluding, persistent distressing dreams increase the risk of developing cognitive impairment or PD in adulthood.
The study's strength was the prospective design, longer follow-up, assessing distressing dreams at two different time periods, etc.
Future studies are warranted for confirmation of these findings and to determine if treating distressing dreams (early life) reduces dementia and PD risk.
Further reading:
https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(23)00049-4/fulltext#%20