Walnuts, melatonin and sleep quality in young adults
What it found
In 76 young adults, eating 40 g of walnuts daily with dinner for 8 weeks raised evening levels of a melatonin by-product in urine and modestly improved some sleep measures.
The authors say walnuts may help promote sleep.
What they found
Studies in people
Evening melatonin by-product
After 8 weeks of eating walnuts, evening urinary 6-SMT rose by about 1.64 ng per mg creatinine compared with baseline. Nighttime 6-SMT did not change significantly.
Sleep latency
Sleep latency fell by about 1.29 minutes after 8 weeks of walnuts compared with baseline. The improvement was seen from week 4.
Global sleep quality
The global sleep quality score improved by 0.30 points after 8 weeks of walnuts compared with baseline. Daytime sleepiness dropped by 1.37 points.
Sleep efficiency
After 8 weeks, sleep efficiency was 0.70% higher during the walnut period than during the control period. The authors report this as a small increase.
Other sleep measures
No significant differences were seen in wake after sleep onset, number of awakenings, or total sleep time between conditions. Participants slept more than 7 hours per day on average throughout the trial.
Other findings
Walnut contents
A 40 g serving of the walnuts used provided an average of 84.6 mg of tryptophan and 118.0 ng of melatonin. The tryptophan to competing amino acid ratio was 0.058.
What the authors conclude
“Our findings highlight the potential of walnuts as sleep-promoting foods among young adults.”
Also in their conclusions
- They say their findings highlight the potential of walnuts as sleep-promoting foods among young adults.
- They state that daily walnut consumption during dinner significantly reduces sleep latency and increases evening urinary 6-SMT concentrations, and that the 8-week intervention positively influenced global sleep quality and reduced daytime sleepiness.
- They call for further research to understand the mechanisms behind the diet-sleep link and to see whether the benefits extend to older adults and people with sleep disorders.
How it was done
The authors wanted to test whether daily walnut consumption could improve sleep quality and affect melatonin production, since walnuts contain tryptophan and plant-based melatonin. They noted that little was known about nuts as sleep-promoting foods.
They ran an 18-week randomised crossover trial in 76 young adults (average age 24.1 years, 85.5% women). Participants ate 40 g of walnuts daily with dinner for 8 weeks or avoided walnuts and other nuts for 8 weeks, with a 2-week washout between. Sleep was tracked with wrist monitors and urine was collected for 6-SMT.
What it can’t tell you
- The participants were young, mostly women, and healthy, so the results may not apply to older adults or people with sleep problems.
- The study could not be blinded because people knew whether they were eating walnuts, which may have influenced how they reported sleepiness.
- The authors did not standardise overall diet or measure dietary tryptophan and melatonin intake, which could affect the interpretation.
Who paid
- Authors work at
- University of Barcelona, Spain
The paper
- Title
- Daily walnut consumption increases 6-sulfatoxymelatonin urinary levels and can improve sleep quality: a randomized crossover trial
- Type
- Randomised controlled trial
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Zerón-Rugerio MF, Ibarra-Picón A, Diez-Hernández M, et al (2025). Daily walnut consumption increases 6-sulfatoxymelatonin urinary levels and can improve sleep quality: a randomized crossover trial. Food & function. doi:10.1039/d5fo00971eFree full textPubMed 40791136DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error