Rapid changes in overnight blood pressure after transitioning to early-morning shiftwork

Risk for adverse cardiovascular events increases when blood pressure does not decrease at night ("non-dipping,"<10% decrease from daytime blood pressure). Shiftwork alters relationships between behaviors and endogenous circadian rhythms (i.e., circadian disruption along with variable sleep timing), and chronic shiftwork increases cardiovascular disease risk. To determine whether transitioning into shiftwork changes the overnight blood pressure dipping pattern, we leveraged a natural experiment that occurs when newly-hired bus operators transition from a daytime training schedule into an early-morning shiftwork or daywork schedule. Twenty participants were studied in a 90-day protocol upon new employment and underwent cardio-metabolic health assessments, including ambulatory blood pressure monitoring, and weekly sleep-wake diaries. Measurements were repeated after ~30 and 90 days after transitioning to a day or an early-morning shiftwork schedule. Newly-hired shiftworkers displayed dramatic changes in overnight blood pressure, with 62% converting from a healthy dipping blood pressure to the nondipping pattern, resulting in 93% of shiftworkers displaying a nondipping phenotype at 90-days. In contrast, 50% of dayworkers had a nondipping profile at baseline and this decreased to 0% at 90-days, a significant difference from shiftworkers (p =. 001). At 90-days, overnight blood pressure dipping was ~7% less in shiftworkers than dayworkers (-6.3% [95%CI -3.7 to -8.8%] vs -13.1% [-10.3 to -15.9%]: p <. 01), with changes in dipping associated with changes in sleep timing variability (r2 =. 28, p =. 03). The observed changes in overnight blood pressure dipping in newly-hired early-morning shiftworkers, which were associated with sleep timing variability, may be an early warning sign of increased cardiovascular risk among shiftworkers. Statement of Significance Shiftworkers have a much higher risk for cardiovascular disease than dayworkers, but it is unknown why this occurs. Using a natural experiment that occurs when newly-hired bus operators transition to either working day or early-morning shiftwork schedules, we show that commonly performed shiftwork results in drastic changes to overnight blood pressure dipping patterns. These changes in blood pressure occur simultaneously with changes in the variability of sleep timing, which may be a potentially modifiable behavior. As the overnight blood pressure pattern is a strong indicator for future cardiovascular disease, these robust changes when starting shiftwork may help to explain the increased risk for cardiovascular disease observed in shiftworkers.