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ABSTRACT
A diminished nocturnal decline in blood pressure (BP) represents a risk factor for cardiovascular disease. To define daytime and nighttime ambulatory BP, clock time-dependent methods are used when information on diary-based sleeping time is unavailable. We aimed to compare fixed-clock intervals with diary records to identify nocturnal BP declines as a predictor of long-term cardiovascular risk among the general population. Data were obtained from 1714 participants with no history of cardiovascular disease in Ohasama, Japan (mean age, 60.6 years; 64.9% women). We defined extreme dippers, dippers, non-dippers, and risers as nocturnal systolic BP decline ≥20%, 10–19%. 0–9%, and <0%, respectively. Over a mean follow-up period of 17.0 years, 206 cardiovascular deaths occurred. Based on diary records, multivariable-adjusted hazard ratios (HRs) for cardiovascular death compared with dippers were 1.24 (95% confidence interval [CI], 0.82–1.87) in extreme dippers, 1.21 (0.87–1.69) in non-dippers, and the highest HR of 2.31 (1.47–3.62) was observed in risers. Using a standard fixed-clock interval (daytime 09:00–21:00; nighttime 01:00–06:00), a nighttime 2 h-early shifted fixed-clock (daytime 09:00–21:00; nighttime 23:00–04:00), or a nighttime 2 h-late shifted fixed-clock (daytime 09:00–21:00; nighttime 03:00–08:00), the HR (95%CI) in risers compared with dippers was 1.57 (1.08–2.27), 2.02 (1.33–3.05), or 1.29 (0.86–1.92), respectively. Although use of diary records remains preferable, the standard and nighttime 2 h-early shifted fixed-clock intervals appear feasible for population-based studies.
Acknowledgments
We are grateful to the residents of Ohasama Town, all related investigators and study staff, and staff members of the Ohasama Town Government, Ohasama Hospital and Iwate Prefectural Stroke Registry for their valuable support of this project.
Funding
This study was supported by Grants for Scientific Research (23249036, 23390171, 24390084, 24591060, 24790654, 25253059, 25461083, 25461205, 25860156, 26282200, 26860093, 16H05243, 16K09472, 16K11850, 16K15359, and 17K15853) from the Ministry of Education, Culture, Sports, Science, and Technology, Japan; a Grant-in-Aid from the Japan Society for the Promotion of Science (JSPS) fellows (25*7756, 25*9328, 26*857, and 27*656); the Japan Arteriosclerosis Prevention Fund; an Intramural Research Fund (22-4-5) for Cardiovascular Diseases of National Cerebral and Cardiovascular Center; and a Health Labor Sciences Research Grant (H26-Junkankitou [Seisaku]-Ippan-001) from the Ministry of Health, Labor, and Welfare.
Declaration of interest
The authors have no conflicts of interest to declare.
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Notes on contributors
Michihiro Satoh
M. Satoh drafted the manuscript. All authors conducted the Ohasama study and commented on the manuscript.