A new randomized controlled trial conducted by researchers at the University of Barcelona suggests that eating a daily serving of walnuts may support improved sleep quality and reduce daytime sleepiness in healthy young adults. The study was published in Food & Function.
The trial involved 76 participants aged 20–28 (85% female) who consumed 40 grams of walnuts daily with dinner over eight weeks, in a crossover design with a control phase. Researchers measured urine biomarkers linked to melatonin, sleep quality parameters such as latency, awakenings, and efficiency, as well as self-reported daytime sleepiness.
The findings showed that walnut consumption boosted a key biomarker of melatonin, significantly increasing evening urine samples after four weeks compared to the control period. On average, participants fell asleep 1.3 minutes faster, reported better overall sleep quality scores, and experienced less daytime sleepiness. However, no significant changes were observed in circadian-related variables.
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"This is the first randomized controlled trial to show that daily walnut consumption measurably improved objective sleep quality and increased melatonin levels during evening hours after an intervention period," said Dr. Maria Izquierdo-Pulido, lead researcher. She noted that insufficient sleep remains a global health concern, with impacts ranging from chronic illness to cognitive and economic effects.
The researchers highlighted walnuts' nutrient profile as a possible explanation. Walnuts contain tryptophan (84.6 mg), a precursor to melatonin, as well as plant-based melatonin (118 ng), magnesium (45 mg), and B vitamins B5 and B6 (0.2 mg each). Dr. María Fernanda Zerón-Rugerio, co-leader of the study, added: "While the observed effects in this study came following walnut consumption at dinner, we believe that the daily intake, rather than the timing, led to the sleep-supportive benefits."
The authors cautioned that the study had limitations, including unmeasured dietary intake of tryptophan and melatonin, restricting the broader applicability of the results. Further research is needed to confirm the findings across different populations, including individuals with sleep disorders.
These initial results add to existing evidence on the role of diet and nutrient-dense foods in influencing sleep health.
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