Extracts from article in New Scientist magazine, 'Keep Having Nightmares? You may be getting too much sleep', 28 July, by Helen Thompson:
"People often have nightmares following upsetting events, and research into nightmares has mostly focused on people with conditions like post-traumatic stress disorder (PTSD). But most people get nightmares at some point, prompting Stephanie Rek at the University of Oxford and her colleagues to perform one of the largest ever studies of nightmares in the general population.
The team recruited 846 people through media advertisements and databases of people interested in sleep studies, and asked them to complete an online survey. The participants were asked questions such as how many nightmares they had experienced over the past two weeks, and how bad they were. These answers contributed to an overall score on a “nightmare severity scale”.
Each volunteer was also assessed for PTSD and asked about other aspects of their life, such as recent divorces or legal trouble, their tendency to worry, how much sleep they get and how much alcohol they drink.
Perhaps unsurprisingly, the team found that worrying about the future, or about doing things wrong, was most strongly associated with the frequency and severity of nightmares. The team suggest that worrying before bedtime feeds negative dream content, increasing the chance of nightmares – in line with the idea that dreams reflect waking life experiences, capturing the daytime concerns of the dreamer.
But the team also found a link between the occurrence of nightmares and sleeping for longer: for example, if you have 9 hours of sleep a night rather than 6, you have more than doubled your chances of having a nightmare. Rek says that sleeping for longer might increase the amount of late-night rapid eye movement (REM) sleep – the time when nightmares most commonly occur. Essentially any 3 hour increase in sleep is associated with more than double the chance of having a nightmares.
Alternatively, worries may not cause nightmares. Instead, it may be that people who have nightmares for some other reason tend to have disrupted sleep, which exacerbates their worries the following day and makes them sleep longer the rest of the week.
Alcohol and exercise didn’t appear to have an association with nightmare occurrence. “This was a surprise,” Rek says. Previous studies have shown that alcohol boosts the amount of REM sleep in the second half of the night, increasing the chances of nightmares. “It warrants more attention,” says Rek.
Read the full story in New Scientist magazine.
Read the paper in Social Psychiatry and Psychiatric Epidemiology.