A new study is putting walnuts in the sleep conversation. Researchers found that young adults who ate 40 grams of walnuts daily with dinner for eight weeks had better sleep quality scores and lower daytime sleepiness than during a control phase, though the study does not prove walnuts are a treatment for sleep issues.
What the study found
The paper, published online on August 12, 2025, and later appearing in the September 15, 2025 issue of Food & Function, examined whether daily walnut intake could affect sleep-related measures in healthy young adults. The trial included a final analytical sample of 76 participants, with a mean age of 24.1 years, and 85.5% of the group were women.
Researchers used an open-label randomized crossover design. Participants either ate 40 grams of walnuts each day with dinner or avoided walnuts and other nuts for eight weeks, then switched after a two-week washout period. That matters because each participant served as their own comparison, which can help reduce some types of variation.
During the walnut phase, the study found a statistically significant increase in evening urinary 6-sulfatoxymelatonin, or 6-SMT, a metabolite used as a marker related to melatonin production. The walnut phase was also linked to significantly better global sleep quality, improved sleep latency, and reduced daytime sleepiness, according to the paper.
What that means for home cooks
For shoppers, the practical takeaway is simple: the amount used in the study was 40 grams a day, roughly a generous handful of walnuts. The study specifically tested walnuts eaten with dinner, not at breakfast or as a general add-on at any time of day.
That said, this is still early evidence. The researchers reported an association between higher evening 6-SMT levels and better sleep efficiency, but the study did not establish the exact biological mechanism behind the change. It also focused on healthy young adults, so the findings may not apply the same way to older adults, children, or people with diagnosed sleep disorders.
Walnuts already have an easy place in many kitchens. They can be sprinkled over oatmeal, folded into yogurt, tossed into salads, or eaten plain as a snack. If someone wants to mirror the study more closely, using them at dinner would be the closest match to the research design.
Why the findings need some caution
Even with encouraging results, the study has limits. It was relatively small, it was open-label rather than blinded, and most participants were women. Those details do not erase the findings, but they do mean the results should be interpreted carefully.
The paper describes walnuts as having potential as a sleep-promoting food among young adults under free-living conditions. That is a measured conclusion, and it is the right one. A food study like this can show a promising link, but it cannot turn a single snack into a proven fix for poor sleep.
For readers deciding what to do with this information, the most grounded answer is also the most practical. Walnuts are an easy pantry staple, and this study suggests they may be worth considering as part of an evening routine, especially for people already looking for simple food-based habits. It is not a medical claim, and more research is still needed before anyone should treat walnuts as a sleep solution.