A first of its kind study uncovers the role walnuts may play as a sleep-supportive, whole food.
ISTANBUL, Türkiye – (ARAB NEWSWIRE) — Eating a daily serving of about one handful of walnuts (40 grams or about 1.5 ounces) with dinner may help improve measures of overall sleep quality and reduce daytime sleepiness in healthy young adults, according to a new randomized controlled trial published in Food & Function.1*
Researchers from the University of Barcelona aimed to study the potential impact that daily walnut consumption could have on specified urine biomarkers (6-SMT, a biproduct of melatonin), sleep quality parameters (sleep latency, wake after sleep onset, awakenings, and efficiency) and daytime sleepiness.
The study evaluated the effects of consuming 40 grams of walnuts daily with dinner over an eight-week period among 76 healthy young adults ages 20-28 (85% female), who completed both walnut and control phases in a crossover design. Researchers found that eating walnuts boosted a key biomarker of the sleep-regulating hormone, melatonin, which was significantly increased in evening urine samples after a four-week intervention period when participants consumed walnuts, as compared to the control period.
The walnut intervention also shortened the time it took participants to fall asleep by 1.3 minutes, improved overall sleep quality scores, and reduced self-reported daytime sleepiness compared to a control, nut-free period. While global sleep quality scores improved, there were no significant differences in measures of circadian-related variables between the intervention and control conditions.
“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 of the study out of the University of Barcelona.”
The researchers explain that walnuts’ unique combination of sleep-supportive nutrients such as tryptophan (84.6 mg) – a precursor to melatonin, plant-based melatonin (118 ng), magnesium (45 mg), and B vitamins (0.2 mg each vitamin B5 and vitamin B6) may help explain the positive outcomes seen in the study.
Dr. María Fernanda Zerón-Rugerio, co-leader of the study explains, “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.”
This study is among the first to demonstrate walnuts’ potential as a sleep-supporting food. As such, the study contained a number of limitations, including unmeasured dietary tryptophan and melatonin intake, that restrict the applicability of the study findings to the general population.
References:
*This research was funded by the California Walnut Commission. The funder made no contribution during the design or implementation of the study, nor in the interpretation of findings or the decision to publish.
- Zerón-Rugerio MF, Ibarra-Picón A, Diez-Hernández M et al. Daily Walnut Consumption Increases 6-Sulfatoxymelatonin Urinary Levels and Can Improve Sleep Quality: A Randomized Crossover Trial [published online ahead of print August 12, 2025]. Food & Function. DOI: 10.1039/d5fo00971e
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