Mechanistic Effect of Walnut Consumption on Sleep Quality

Walnuts are a nutrient-rich food which provides melatonin and polyphenols. While there is evidence that dietary intakes of foods high in melatonin and polyphenols positively influence sleep quality, the effect of walnuts has not been investigated. The investigators propose to fill this knowledge gap by testing the effects of walnut consumption on serum melatonin and resulting sleep and circadian biology. The study hypotheses are that walnut consumption for 4 days will increase melatonin levels, suggestive of more robust circadian rhythms, and lead to better sleep quality compared to a high-carbohydrate high-sugar (HCHS) equivalent. Using a randomized controlled crossover trial, the study aims to: 1) determine the effect of walnut vs HCHS consumption on melatonin levels; and 2) determine the effect of walnut vs HCHS consumption on sleep and circadian physiology. Adult males and females with poor sleep quality will consume three servings/day of walnuts or an equicaloric HCHS food for 4 days. Sleep quality will be measured nightly using the Karolinska Sleep Diary and wrist actigraphy; sleep architecture from polysomnography will be measured on night 3. Circadian physiology will be assessed on day 4 using body temperature and hourly serum melatonin and on the morning of day 5 from overnight urinary 6-sulfatoxymelatonin. Given the extent of poor sleep, our findings may open new avenues to improve sleep health from increased walnut consumption.

Inclusion criteria

• Equal numbers of men and women (12 male and 12 post-menopausal female)
• Equal number of individuals with normal weight (18.5-24.9 kg/m2) and overweight (25-29.9 kg/m2)
• Participants will self-report poor sleep quality, reflected by a global score >5 on Pittsburgh Sleep Quality Index

Exclusion criteria

• Diagnosed sleep disorder
• Participants with conditions that could affect sleep will be excluded:

• smoking, excessive caffeine intake (>300 mg/day)
• shift work
• chronic pain
• diagnosis of a chronic disease (e.g., uncontrolled hypertension, pre-diabetes, type 2 diabetes, chronic kidney disease, chronic obstructive pulmonary disease),
• autoimmune diseases
• cardiovascular event or cancer in the past 24 months
• psychiatric/neurologic disease or disorder, or sleep disorder (diagnosed or high risk for sleep apnea, chronic insomnia, restless leg syndrome, narcolepsy)
• use of medications that influence CYP1A2 enzymes
• Allergy/intolerance to nuts, tree nuts, or unwilling to eat study foods