Twenty-four hours light exposure experiences in postpartum women and their 2–10-week-old infants: An intensive within-subject design pilot study

Abstract

Background Adequate light exposure is critical for entraining circadian rhythms, regulating sleep–wake cycles, and maintaining optimal mood. Yet, few studies have reported normative data on light exposure experiences in postpartum women and young infants; none has examined the two simultaneously. Objectives The objective of this pilot study was to document the 24-h light exposure experiences in postpartum women and their infants. Design An intensive within-subject design was employed. Settings The participant’s natural home environment. Participants Twenty-four healthy mother–infant pairs were recruited from the general community in Seattle, USA. Two mother–infant pairs did not have complete data, resulting in a final sample size of 22 (12 female infants). Methods Mothers and infants wore a monitor to continuously record illumination levels for 7 days. Data were aggregated within subject to calculate summary measures of illumination exposure. Circadian patterns of light were examined using cosinor analysis. Pearson correlation was used to examine the relation between maternal and infant light exposure. Results Mothers spent 71.13 ± 11.58% and infants spent 80.07 ± 8.27% of their daytime hours (defined as 06:00–21:59) in an illumination level <50 lux. Mean minutes >1000 lux per day was 54 ± 39 for mothers and 23 ± 18 for infants. Maternal and infant light exposure exhibited a modest circadian pattern and a strong correlation, both in the timing of peak illumination exposure ( r = 0.93, p < 0.01) and in the level of light exposure ( r = 0.70 ± 0.07). Conclusions Postpartum women and infants experience low ambient light levels with short periods of bright light during the day. Whether this level of light is sufficient for optimal postpartum mood and infant circadian entrainment warrants further investigation. If higher levels of light were indeed necessary for postpartum women and young infants, increasing ambient light levels through the use of natural sunlight (i.e., walking outdoors) could be a simple and economic nursing intervention. The strong pattern synchrony between maternal and infant light exposure suggests that mothers play the primary role in providing a lighting environment suitable for infants to synchronize their circadian rhythms to a 24-h day.