Harvard Study Finds Melatonin May Improve Daytime Sleep in Shift Workers and Travelers Interview with:

Jeanne Duffy, MBA, PhD Associate Professor of Medicine Division of Sleep and Circadian Disorders Harvard Medical School

Dr. Duffy

Jeanne Duffy, MBA, PhD
Associate Professor of Medicine
Division of Sleep and Circadian Disorders
Harvard Medical School  What is the background for this study? 

Response: Aging is associated with changes in sleep timing, quality and duration, and even older adults without chronic medical problems have shorter and more disrupted sleep than young adults. Many prescription sleep aids increase the risk of nighttime falls, have

adverse effects on next‐day cognition, and are associated with increased mortality, and so are not recommended for long-term use in older adults. In previous studies, we and others have shown that melatonin, a hormone secreted at night, increases sleep duration in young adults but only when administered during the day when endogenous melatonin levels are low. We wanted to explore whether melatonin could improve the sleep of healthy adults and whether, like young adults, its impact depends on when during the day the person is trying to sleep.  How is melatonin obtained? 

Response: In this study we had the Investigational Drug Service of our hospital’s Pharmacy prepare the melatonin and matching placebo capsules for the study.  What are the main findings?

Response: We found that both doses of melatonin we tested were able to improve sleep when it occurred during the biological daytime (when endogenous melatonin is not present). The 5mg dose of melatonin was also able to improve sleep when it was scheduled during the biological nighttime (when endogenous melatonin was present), mainly by increasing the duration of stage 2 nonREM sleep and slightly shortening awakenings.

These findings contrast with a similar study we carried out previously in healthy young adults, where we did not find any improvements in sleep at night, even with a 5mg dose of melatonin. They also contrast with some prior studies in older adults that did not find any improvements in sleep at night, although those prior studies typically used smaller doses of melatonin. What should readers take away from your report?

Response: That melatonin may improve the sleep of older adults who are trying to sleep during the biological daytime (shift workers, travelers) and it may also improve sleep at night. What recommendations do you have for future research as a result of this work?

Response: We hope to test nighttime effects of melatonin in older adults with and without sleep complaints, and also to test different doses to find the lowest dose that can still improve sleep. 

Disclosures: Czeisler is/was a paid consultant to Physician’s Seal, Tencent Holdings, and Teva Pharma, and is a paid consultant and holds an equity interest in With Deep and Vanda Pharmaceuticals Inc., is/was an expert witness in legal cases, including those involving Vanda Pharmaceuticals; serves as the incumbent of an endowed professorship provided to Harvard University by Cephalon, Inc., which was acquired by Teva Pharma; and receives royalties from Philips Respironics for the Actiwatch-2 and Actiwatch Spectrum devices.


Duffy JF et al. “High dose melatonin increases sleep duration during nighttime and daytime sleep episodes in older adults” Journal of Pineal Research. DOI: 10.1111/jpi.12801 

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Last Updated on May 24, 2022 by Marie Benz MD FAAD