Growing evidence shows that common dietary patterns can affect sleep quality and contribute to insomnia.
I am a nutritional epidemiologist and am trained to look at population-level diets and how they affect health.
In the US, a large percentage of the population suffers from poor sleep quality and sleep disorders such as insomnia and obstructive sleep apnea, a condition in which the upper airways become blocked and breathing stops during sleep. At the same time, most Americans eat far too many fatty and processed foods, too little fiber and too few fruits and vegetables.
While it is difficult to determine whether these two trends are causally linked, more and more research points to links between sleep and diet and provides hints about the biological underpinnings of these relationships.
How nutrition and sleep quality can be intertwined
My colleagues and I wanted to gain a deeper understanding of the possible link between sleep and diet in Americans aged 18 and older. That's why we analyzed whether people who follow the government's dietary guidelines for Americans get more hours of sleep.
Using a nationally representative data set of studies collected between 2011 and 2016, we found that people who did not adhere to dietary recommendations, such as consuming adequate servings of fruits, vegetables, legumes and whole grains, had shorter sleep duration.
In a separate study, we followed more than 1,000 young adults ages 21 to 30 who participated in a web-based dietary intervention study designed to help them increase their daily servings of fruits and vegetables. We found that those who increased their fruit and vegetable consumption over a three-month period reported better sleep quality and a reduction in insomnia symptoms.
Research conducted by my group and others outside the US also shows that healthier overall diets are associated with better sleep quality and fewer insomnia symptoms. These include the Mediterranean diet - a diet rich in plant foods, olive oil and seafood, and low in red meat and added sugars - and anti-inflammatory diets. These are similar to the Mediterranean diet, but place extra emphasis on certain components in the diet, such as flavonoids, a group of compounds found in plants that have been shown to lower inflammatory biomarkers in the blood.
Decomposing the foods and nutrients
Within overall healthy diets, there are numerous individual foods and nutrients that may be linked to sleep quality, with varying evidence.
For example, studies have linked consumption of oily fish, dairy, kiwis, tart cherries and other berries such as strawberries and blueberries with better sleep. One of the most common ways these foods can affect sleep is by providing melatonin, an important modulator of the brain's sleep-wake cycles.
High-fiber foods such as beans and oatmeal and certain protein sources - especially those high in the amino acid tryptophan, such as poultry - have also been linked to better sleep quality. Individual nutrients that may be helpful include magnesium, vitamin D, iron, omega-3 fatty acids and manganese. Some foods, such as salmon, are sources of multiple nutrients.
Untangling the complexity
An important caveat to much research on individual foods, as well as dietary patterns, is that most studies cannot easily disentangle the direction of the relationships.
In other words, it's difficult to know whether the association is due to diet affecting sleep, or from an effect of diet affecting sleep. The reality is that it's likely a cyclical relationship, with a healthy diet promoting good sleep quality, which in turn helps reinforce good nutritional habits.
In observational studies, there are also potential confounding factors, such as age and economic status, which may have important correlations with both sleep and diet.
Foods to avoid for healthy sleep
Aiming for a higher intake of sleep-promoting foods is not necessarily sufficient for better sleep. It is also important to avoid certain foods that can be bad for sleep. Here are some of the main culprits:
- Saturated fats, such as those found in burgers, fries and processed foods, can lead to less restorative sleep, which is considered the most restorative sleep.
- Refined carbohydrates, such as those in white bread and pasta, are metabolized quickly. If you eat these foods for dinner, they can cause you to wake up hungry.
- Alcohol disrupts sleep quality. Although the sedative effects of alcohol may make it easier to fall asleep initially, it disrupts sleep patterns by shortening the amount of REM, or rapid eye movement, sleep in the first part of the night and leading to more nighttime awakenings.
- Caffeine consumed even six hours before bedtime can make it difficult to fall asleep because it blocks the hormone adenosine, which promotes drowsiness.
- The consistent overconsumption of calories can lead to weight gain, one of the strongest predictors of obstructive sleep apnea. Being overweight is a factor because it can put extra pressure on the diaphragm and lungs, and can also lead to a narrower airway as fat builds up around the neck and throat.
Interestingly, our group recently showed that toxins in food or food packaging, such as pesticides, mercury and phthalates - chemicals used to manufacture plastics - can affect sleep. Because toxins are found in both healthy and unhealthy foods, this research suggests that some foods may contain a mix of components that are both beneficial and harmful to sleep.
Meal timing and gender considerations
The timing and consistency of eating, known in sleep research as 'chrononutrition', also likely helps explain the associations between healthy eating and good sleep.
In the US, eating conventional meals, as opposed to random snacks, has been linked to better sleep. Additionally, eating late at night is typically associated with unhealthier food intake - such as processed snacks - and can cause more fragmented sleep.
A final and very interesting piece of this puzzle is that the associations between diet and sleep often differ by gender. For example, it appears that the associations between healthy diets and insomnia symptoms might be stronger in women. One reason for this may be gender differences in sleep. Women in particular suffer from insomnia more often than men.
Keys to a good night's sleep
In general, there is no one magical food or drink that will improve your sleep. It's better to focus on overall healthy eating patterns throughout the day, consuming a greater portion of calories earlier in the day.
And in addition to avoiding caffeine, alcohol, and heavy meals in the two to three hours before bed, the last few hours of the day should also include other good sleep hygiene practices.
These include disconnecting from technology, reducing light exposure and creating a comfortable and relaxing sleep environment. Additionally, it is essential that you allow enough time for sleep and that you maintain a consistent bedtime and wake-up time.
