Light is beneficial for infant circadian entrainment: an actigraphic study.

Aim: This article is a report of an exploratory study of the relation between light exposure and circadian rest-activity patterns in infants.

Background: Ambient light is a major environmental stimulus for regulation of circadian rhythm of sleep and wake in adults, but few studies have been conducted to examine environmental light exposure in relation to rest-activity circadian rhythm parameters of infants.

Methods: An intensive within-subject design was used with a convenience sample of 22 infants (mean postnatal age 49·8 days) who wore a combined light and activity monitoring device for seven consecutive days at home. For each infant, light data (lux) were aggregated over the 7 days into categories of illumination and expressed in mean minutes/day. Circadian light and activity parameters, including mesor, amplitude, acrophase and R(2) cosinor fit, were determined using cosinor analysis. Associations between light exposure and circadian rest-activity rhythm parameters were examined using correlation and regression analyses. Data were collected between 2006 and 2007.

Results: Infants spent only one-eighth of their daytime hours in an environment with >100 lux light level. There was a relatively large statistically significant relation between the acrophase of light exposure and the acrophase of activity. Increased duration of daily exposure to >100 lux of illumination, and increased amplitude of circadian rhythm of light were associated with stronger circadian patterns of infant activity.

Conclusion: Results suggest an association between light and activity patterns and that increasing duration of exposure to moderate light levels may be a simple and economical nursing intervention during the early postnatal weeks.