Daily walnut intake, melatonin levels and sleep in young adults
What it found
Eating 40 g of walnuts each day raised a melatonin marker in urine and improved sleep quality in young adults.
It also reduced daytime sleepiness.
What they found
Studies in people
Melatonin marker in urine
Evening urine levels of a melatonin breakdown product rose after 8 weeks of eating walnuts. Levels did not change during the nut-free period.
Falling asleep faster
People fell asleep more quickly when they ate walnuts daily. No change was seen during the control period without nuts.
Overall sleep quality
Global sleep quality scores improved during the walnut period. Daytime sleepiness scores also dropped.
Melatonin linked to sleep
Higher evening levels of the melatonin marker were tied to better sleep efficiency and better overall sleep quality during the walnut period.
Other findings
Walnut nutrient content
Researchers measured tryptophan and melatonin in the walnuts used for the trial using lab equipment.
What the authors conclude
- They suggest walnuts may help promote better sleep in young adults.
- They found that a daily 40 g serving raised melatonin markers in urine, shortened the time needed to fall asleep and improved overall sleep quality.
- They say more research is needed to understand how diet and sleep are connected.
How it was done
The authors wanted to see if eating walnuts every day could change levels of a melatonin breakdown product in urine and affect how well people sleep.
Seventy-six young adults with an average age of 24.1 years took part, and 85.5% were women. They either ate 40 g of walnuts with dinner or avoided all nuts for 8 weeks, then switched after a 2-week break. Researchers measured melatonin markers in urine, tracked sleep details and checked daytime sleepiness.
What it can’t tell you
- We summarised it from the abstract only.
- This trial only included young adults, so it cannot show whether older people would see the same sleep changes.
- The study lasted 8 weeks per phase, so longer-term effects of eating walnuts on sleep remain unknown.
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
- Abstract only
- 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/d5fo00971ePubMed 40791136DOI
Summary written 1 Oct 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error