Altered circadian rhythm of blood pressure in shift workers.

The effect of shift work on the circadian rhythm of blood pressure (BP) was studied in male bakery workers. The study group consisted of 28 men, blue collar non-rotating shift workers, 20-60 years of age, and the control group comprised 30 men, blue collar, day workers in the same age group. BP was evaluated in all subjects by 24h BP monitoring. Day workers showed typical circadian rhythm with a drop in both systolic and diastolic BP at night. This pattern was reversed in night workers. The peak SBP for night workers was at 11 pm and among day workers at 4 pm. Peak DBP was recorded among night workers at 10 pm and among day workers at 3 pm. All subjects showed a highly significant cyclic variation in BP. Whereas the range for SBP was similar in these two age groups (P > 0.05), the amplitude of DBP tended to be smaller in young workers. Therapeutic decisions for night shift workers with hypertension should take into account their altered BP cycle.