- A new study suggests that snacking on walnuts may improve sleep and melatonin levels.
- Participants in the study ate around 1/2 cup of walnuts each day for eight weeks.
- Add walnuts to snack mixes, salads and breakfast dishes, or snack on them solo.
Poor sleep can affect just about anyone, and research has linked it to health conditions like obesity and heart disease. Interestingly, research shows that poor sleep is also connected to unhealthy eating habits. On the flip side, studies suggest that eating a healthier diet, especially one rich in plant-based foods like nuts, may improve sleep quality.
Many nuts are a natural source of tryptophan, an essential amino acid that helps produce melatonin, the hormone responsible for regulating our sleep-wake cycle. Nuts, particularly walnuts, also contain plant-based melatonin, which has been shown to increase melatonin levels in the body after consumption. This makes them a promising natural option for improving sleep—but there has been a knowledge gap regarding whether walnut consumption truly impacts sleep parameters.
To explore the potential sleep benefits of walnuts, researchers designed a study to see if eating them regularly is linked to improved sleep patterns and increased levels of 6-SMT, a marker of melatonin, in young adults. These results were published in Food & Function.
How Was This Study Conducted?
This study was designed as an 18-week randomized crossover trial to explore whether regular walnut consumption could improve sleep quality. Young adults between the ages of 20 and 35 were recruited, and after screening, 76 participants completed the study.
Participants were randomly assigned to one of two groups. In the intervention phase, participants consumed 40 grams of walnuts daily with dinner for eight weeks. Walnuts were provided in pre-portioned packages, and participants were instructed to avoid other nuts or nut-based products during this time. In the control phase, participants refrained from consuming any nuts or nut-based products for eight weeks. After completing one phase, participants underwent a 2-week washout period before switching to the other phase.
Throughout the study, all participants followed a Mediterranean-style diet and received sleep hygiene recommendations, such as avoiding caffeine and alcohol in the evening, limiting screen time before bed and maintaining consistent sleep and meal schedules.
To assess sleep quality, participants wore wrist-worn actigraphy monitors for seven consecutive days during each phase. These devices tracked sleep patterns, activity levels, skin temperature and light exposure. Participants also provided urine samples during the study to measure levels of 6-sulfatoxymelatonin (6-SMT), a marker of melatonin production. Researchers used the data collected to analyze potential associations between walnut intake and sleep outcomes.
Walnut samples were analyzed to quantify their tryptophan and melatonin content. Researchers also examined the ratio of tryptophan to other large neutral amino acids (CAAs), as a higher ratio may enhance tryptophan’s ability to cross the blood-brain barrier and promote sleep.
What Did The Study Find?
This study revealed that eating 40 grams of walnuts daily for eight weeks led to significant improvements in sleep quality and melatonin production. (For snacking purposes, 40 grams of walnuts would be just under ½ cup of walnut halves, or around 20 walnut halves.)
Walnuts were found to be a rich source of sleep-promoting nutrients, providing an average of 84.6 mg of tryptophan and 118.0 ng of melatonin per serving. The tryptophan-to-competing amino acid (CAA) ratio in walnuts was 0.058. That ratio is important, as a higher ratio helps tryptophan cross the blood-brain barrier, where it can be converted into melatonin, according to the authors.
The study participants, who were mostly young women with an average age of 24, began the trial with a baseline global sleep quality score of 2.8 out of 4, meaning their sleep quality was moderate but had room for improvement. After eight weeks of walnut consumption, participants experienced several notable improvements in their sleep patterns:
- Sleep latency, or the time it takes to fall asleep, decreased significantly.
- Sleep efficiency, which measures the percentage of time in bed spent actually sleeping, increased by 0.7% after eight weeks of walnut consumption.
While this may seem like a small change, even slight improvements in sleep efficiency can have meaningful effects on overall sleep quality. Through analysis of urine samples, the study also found that walnut consumption was linked to a significantly increased melatonin production. And in addition to improving sleep latency and efficiency, walnut consumption was also linked to reduced daytime sleepiness. The researchers suggest that walnuts may have a cumulative effect on overall sleep quality, even if some individual parameters remained unchanged.
While this study provides valuable insights, there are a few limitations to consider. First, because the intervention involved eating walnuts, it was difficult to blind participants—meaning they knew whether they were in the walnut or control phase. This could have influenced their behavior or perceptions. Additionally, the study did not standardize participants’ overall diets, which means variations in what they ate outside of the intervention could have affected the results. Another limitation is that the study did not track how much tryptophan or melatonin participants consumed from other foods, which might have influenced the findings.
It is also important to note that this project was financed by the California Walnut Commission and by the Institute for Research in Nutrition and Food Safety of the University of Barcelona. However, neither the California Walnut Commission nor the Institute had any role in the study design, analysis or interpretation of the data.
How Does This Apply To Real Life?
If you’re someone who struggles with falling asleep or staying asleep, this study offers a simple and natural strategy to consider: adding walnuts to your diet. The findings from this study suggest that walnuts, which are a source of tryptophan and melatonin, may help improve sleep quality by supporting the body’s natural sleep-wake cycle. Eating just 40 grams of walnuts daily, or about a handful, may help you fall asleep faster, sleep more efficiently and even feel less groggy during the day.
And you don’t have to eat the walnuts on their own—incorporate them into a nice salad, a simple trail mix, a cozy breakfast of oatmeal or a yogurt parfait with fruit. We also love preparing them with a little sugar and spice, like in our Spiced Roasted Walnuts recipe, if you enjoy snacking on seasoned nuts.
That said, it’s important to remember that sleep challenges can stem from a variety of factors, such as stress, medical conditions or lifestyle habits. While walnuts may not be a magic solution for everyone, they can be a simple, nutritious option that could complement other healthy sleep practices, like maintaining a consistent bedtime and limiting screen time before bed. What makes walnuts especially practical is how easy they are to incorporate into your daily routine, whether as a snack, in a salad, or alongside dinner. While they may not address every sleep issue, they could be a helpful addition to your toolkit for better rest.
Our Expert Take
This study published in Food & Function highlights the potential of walnuts as a natural way to support better sleep. When eating 40 grams of walnuts daily for eight weeks, participants experienced improvements in how quickly they fell asleep, how efficiently they slept and even how alert they felt during the day. The study also showed that walnuts increased melatonin production, particularly in the evening, which is key for initiating sleep. These findings suggest that walnuts could be a simple and accessible addition to a healthy lifestyle for those looking to improve their sleep quality.
