Later circadian timing and increased sleep timing variability are associated with attenuations in overnight blood pressure dipping among chronic nightshift workers.

OBJECTIVE: Determine relationships between overnight blood pressure, circadian phase, and sleep variability among dayshift and chronic nightshift nurses. METHODS: Twenty participants working dayshift (n = 10) or nightshift (n = 10) schedules participated in a 7-day cross-sectional study. Participants underwent an evening in-laboratory melatonin assessment and wore ambulatory blood pressure devices to assess 24-hour blood pressure patterns. Overnight blood pressure dipping was calculated from sleeping/waking systolic blood pressure ratio and salivary dim-light melatonin onset determined circadian phase. Sleep variability was assessed using the standard deviation of 7-day sleep onset. RESULTS: Nightshift workers had later circadian phase, greater sleep onset variability, and an attenuated overnight blood pressure dipping pattern. Later circadian phase was associated with attenuated dipping patterns and sleep onset variability was negatively correlated with blood pressure dipping magnitude in nightshift, but not dayshift workers. CONCLUSIONS: Chronic circadian disruption via higher sleep onset variability among nightshift workers may contribute to attenuated blood pressure dipping and cardiovascular risk in this population.