Daytime midpoint as a digital biomarker for chronotype in bipolar disorder

J Affect Disord. 2018 Dec 1;241:586-591. doi: 10.1016/j.jad.2018.08.032. Epub 2018 Aug 10.


Background: Bipolar disorder (BD) is associated with later sleep and daily activity (evening rather than morning chronotype). Objective chronotype identification (e.g., based on actigraphs/smartphones) has potential utility, but to date, chronotype has mostly been assessed by questionnaires. Given the ubiquity of accelerometer-based devices (e.g. actigraphs/smartphones) worn/used during daytime and tendency to recharge rather than wear at night, we assessed chronotype using daytime (rather than sleep) interval midpoints.

Methods: Sixty-one participants with BD type I (BD-I) or II (BD-II) and 61 healthy controls completed 25-50 days of continuous actigraphy. The Composite Scale of Morningness (CSM) was completed by a subset of this group. Daytime activity midpoint was calculated for each daytime interval, excluding naps. Evening chronotype was defined as having a daytime interval midpoint at or after 16:15:00 (4:15:00 PM).

Results: BD versus controls had delayed daytime midpoint (mean ± standard deviation) (16:49:07 ± 01:26:19 versus 16:12:51 ± 01:02:14, p < 0.01), and greater midpoint variability (73.3 ± 33.9 min versus 58.1 ± 18.3 min, p < 0.01). Stratifying by gender and age, females and adolescents with BD had delayed and more variable daytime midpoints versus controls. Adults with BD had greater midpoint variability than controls. Within-person mean and standard deviations of daytime midpoints were highly correlated with sleep midpoints (r = 0.99, p < 0.01 and r = 0.86, p < 0.01, respectively). Daytime midpoint mean was also significantly correlated with the CSM (r = -0.56, p < 0.01).

Limitations: Small sample size; analyses not fully accounting for daytime napping.

Conclusions: Wrist actigraphy for determination of daytime midpoints is a potential tool to identify objective chronotype. Exploration of the use of consumer devices (wearables/smartphones) is needed.

Keywords: Actigraphy; Bipolar disorder; Chronotype; Daytime.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Actigraphy
  • Adolescent
  • Adult
  • Biomarkers*
  • Bipolar Disorder / psychology*
  • Chronobiology Disorders / psychology*
  • Circadian Rhythm*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Sleep
  • Surveys and Questionnaires
  • Young Adult


  • Biomarkers