California Walnut Commission: 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. With these findings, the researchers suggest that walnut consumption could potentially be a simple, food-based approach to supporting healthy sleep.
“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. “With over one in three American adults not meeting the recommended amount of sleep per night,2 our results open the door to future research in other age groups and in people with sleep disorders.” Insufficient sleep is seen as a global health concern, with multi-faceted public health implications, ranging from chronic illness to cognitive and economic impacts.3
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. These findings suggest walnuts may help naturally support sleep quality, though more research is needed to understand the mechanism.
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. While further research is warranted to examine these effects, these initial findings add to the growing body of evidence supporting the role of diet and specific nutrient-dense foods, such as walnuts, in promoting sleep health.
Here are some easy ways to add a handful of walnuts to your evening meal:
- Enjoy a dinnertime staple like meatballs, and serve them with a flavorful, satisfying twist with these Greek Walnut Meatballs with Tzatziki Sauce.
- California Walnut Chili made with beans, veggies, and walnuts contains a combination of fiber, plant-based protein and good fats – a trio that can help keep blood sugar steady through the night, preventing 2 AM hunger wake-ups.
- Sprinkle chopped walnuts over oatmeal, salads, or roasted vegetables for a boost of texture, flavor, and nutrition.
- Blend walnuts into smoothies, stir them into yogurt, or use them as a crust for chicken or fish for an easy upgrade to everyday meals.
