If you find that eating certain foods causes you to sleep poorly, you are not alone—and there may be a physical cause for your bad dreams. Scientists who studied the link between diet, sleep problems, and cultural beliefs about food and sleep found that healthier evening eating habits lead to better sleep and better dream recall, while consuming dairy products is associated with nightmares. This is thought to be due to lactose intolerance causing nighttime digestive issues, which in turn affect people’s dreams.

Bad Dreams due to Lactose Intolerance

In fact, researchers have found that consuming too many dairy products can disrupt sleep. The researchers surveyed more than 1,000 students about the quality of their sleep, their eating habits, and any perceived connection between the two, and found a strong link between nightmares and lactose intolerance — possibly because bloating or stomach pain during the night affects people’s dreams.

“The severity of nightmares is closely related to lactose intolerance and other food allergies,” said Dr. Tore Nielsen of the Université de Montréal, lead author of the article in Frontiers in Psychology. “These new findings suggest that changing dietary habits in people with certain food intolerances could alleviate nightmares. They could also explain why people so often blame dairy products for bad dreams!”

Although there has long been a popular belief that diet affects sleep, there is very little evidence to confirm or refute this. To investigate this, the researchers surveyed 1,082 students at MacEwan University. They asked them about their sleep duration and quality, their dreams and nightmares, and any possible connection between different types of dreams and different foods. They also inquired about the participants’ mental and physical health and their relationship with food.

About one-third of respondents reported having nightmares on a regular basis. Women remembered their dreams more often and reported poor sleep and nightmares more frequently. They also reported food intolerances or allergies almost twice as often as men. About 40% of participants said they believed that eating late or certain foods affected their sleep. About 25% believed that certain foods could worsen their sleep. People who ate less healthily had more negative dreams and remembered their dreams less often. “We are regularly asked whether food affects dreaming – especially by journalists on holidays when food is the focus,” said Nielsen. “Now we have some answers.”

Consuming Dairy Products can Trigger Gastrointestinal Disorders, Which Disrupt Sleep

Most participants who attributed their sleep disturbances to food cited sweets, spicy foods, or dairy products as the cause. Only a relatively small proportion—5.5% of respondents—believed that their diet influenced the tone of their dreams, but many of these individuals reported that sweets or dairy products made their dreams more disturbing or bizarre.

When the authors compared reports of food intolerances with reports of bad dreams and poor sleep, they found that lactose intolerance was associated with gastrointestinal symptoms, nightmares, and poor sleep quality. It is possible that consuming dairy products triggers gastrointestinal disturbances, and the resulting discomfort affects people’s dreams and sleep quality.

“Nightmares are worse for people with lactose intolerance who experience severe gastrointestinal symptoms and have disturbed sleep,” Nielsen said. “This makes sense, because we know that other physical sensations can influence dreaming.” Nightmares can be very disturbing, especially when they occur frequently, as they wake people from sleep in a dysphoric state. They can also lead to sleep avoidance behavior. Both symptoms can prevent restful sleep.

How Diet and Sleep are Related

This could also explain why fewer participants reported a link between their diet and their dreams than in an earlier study by Nielsen and his colleague Dr. Russell Powell of MacEwan University, conducted eleven years earlier with a similar population. Greater awareness of food intolerances could mean that the students in the current study ate fewer foods that trigger their intolerances and could impair their sleep. If this is the case, simple dietary measures could potentially help improve people’s sleep and overall health.

However, aside from the clear link between lactose intolerance and nightmares, it is unclear how the relationship between sleep and diet works. It is possible that people sleep worse because they eat less well, but it is also possible that people do not eat well because they do not sleep well, or that another factor influences both sleep and diet. Further research is needed to confirm these links and identify the underlying mechanisms.

“We need to study more people of different ages, from different walks of life, and with different dietary habits to determine whether our findings are truly transferable to the broader population,” Nielsen said. According to the researchers, experimental studies are also needed to determine whether people can actually perceive the effects of certain foods on their dreams. The experts would like to conduct a study in which they ask people to consume cheese products compared to control foods before going to bed to see if this changes their sleep or dreams.