• Giovanni Cizza, Paolo Piaggi, Kristina I Rother, Gyorgy Csako, and Sleep Extension Study Group.
• Section on Endocrinology & Genetics, Program on Developmental Endocrinology & Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland, United States of America.
• Plos One. 2014 Jan 1;9(8):e104176.

ObjectiveTo evaluate the effects of study participation per se at the beginning of a sleep extension trial between screening, randomization, and the run-in visit.DesignSubjects were screened, returned for randomization (Comparison vs. Intervention) after 81 days (median), and attended run-in visit 121 days later.SettingOutpatient.PatientsObese (N = 125; M/F, 30/95; Blacks/Whites/Other, N = 73/44/8), mean weight 107.6±19.7 kg, <6.5 h sleep/night.InterventionNon-pharmacological sleep extension.MeasurementsSleep duration (diaries and actigraphy watch), sleep quality (Pittsburgh Sleep Quality Index), daily sleepiness (Epworth Sleepiness Scale), fasting glucose, insulin and lipids.ResultsPrior to any intervention, marked improvements occurred between screening and randomization. Sleep duration increased (diaries: 357.4 ±51.2 vs. 388.1±48.6 min/night; mean±SD; P<0.001 screening vs. randomization; actigraphy: 344.3 ±41.9 vs. 358.6±48.2 min/night; P<0.001) sleep quality improved (9.1±3.2 vs. 8.2±3.0 PSQI score; P<0.001), sleepiness tended to improve (8.9±4.6 vs. 8.3±4.5 ESS score; P = 0.06), insulin resistance decreased (0.327±0.038 vs. 0.351±0.045; Quicki index; P<0.001), and lipids improved, except for HDL-C. Abnormal fasting glucose (25% vs. 11%; P = 0.007), and metabolic syndrome (42% vs. 29%; P = 0.007) both decreased. In absence of intervention, the earlier metabolic improvements disappeared at the run-in visit.LimitationsRelatively small sample size.ConclusionsImprovements in biochemical and behavioral parameters between screening and randomization changed the "true" study baseline, thereby potentially affecting outcome. While regression to the mean and placebo effect were considered, these findings are most consistent with the "Hawthorne effect", according to which behavior measured in the setting of an experimental study changes in response to the attention received from study investigators. This is the first time that biochemical changes were documented with respect to the Hawthorne effect. The findings have implications for the design and conduct of clinical research.Trial RegistrationClinicalTrials.gov NCT00261898.

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