Sweet dreams soured by dairy, researchers say

Credit: Dina Nasyrova, Pexels

A new Canadian study suggests that consuming dairy may increase the likelihood of nightmares and poor-quality sleep.

The research, published in Frontiers in Psychology Tuesday, examined self-reported links between eating habits, gastrointestinal discomfort, and dreaming in more than 1,000 students at MacEwan University in Edmonton.

About a third of respondents said they experienced regular nightmares. Among them, those with food sensitivities, and particularly lactose intolerance, were significantly more likely to report both disturbed sleep and emotionally intense or negative dreams.

“The severity of lactose intolerance symptoms was associated with the severity of nightmare disorders,” said Dr. Tore Nielsen, lead author and director of the Dream and Nightmare Laboratory at Université de Montréal, in a video interview with CTVNews.ca. “So, the more severe the symptoms, the more severe the nightmare problem.”

Participants filled out extensive questionnaires that asked about food sensitivities, sleep habits, dream recall, emotional tone of dreams, and general health. Researchers also gathered data on eating patterns and diet quality, categorizing participants as having healthier or less healthy eating habits.

Unhealthy eaters, defined as those who frequently consumed fast food, skipped meals or ate late in the evening, were more likely to experience negative dreams, even if they weren’t classified as full nightmares.

“Unhealthy eating was in fact associated with more nightmares and with more negative dreams in general,” Nielsen said.

While only a small proportion of respondents said they believed food directly influenced their dreams, many of those who did blamed dairy, spicy foods or sweets. Nielsen noted that desserts were the most frequently cited culprits, followed by dairy, though the two categories may overlap.

“Desserts are often made with dairy,” he said. “So, it’s very likely that dairy is even part of that dessert group (blamed by the respondents).”

Self-reported lactose intolerance stood out as the strongest dietary factor associated with nightmares, followed by food allergies more broadly.

While the study found “a significant association between food allergies and nightmares,” Nielsen said the sample size for that group was too small to draw robust conclusions.

The study also included questions about late-night and evening eating.

“We were quite interested in a phenomenon known as night eating,” Nielsen said. “So, people get out of bed and go and get a snack out of the fridge and eat it and then go back to bed without any awareness of having done it.”

Though only a small number of participants reported night eating behaviours, evening eating was common and contributed to the “unhealthy eating” classification used in the study.

“There is evidence that eating certain foods before bed can affect your sleep,” Nielsen said. “But the evidence for dreaming is not as strong.”

He cautioned that self-reported data, particularly around what foods participants consumed and when, is inherently limited. While many people may suspect that what they eat affects their dreams, establishing a clear cause-and-effect relationship requires controlled experiments.

“The only way we can really do that is with experimental studies where we have different groups eating different kinds of food before bed or not before bed, and then comparing the groups to see how their dreams change.”