This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Most systems in the body have a rhythm, a daily cycle. Interrupting that rhythm can have detrimental consequences. Shifting sleep cycles can alter mental status and increase errors that result in accidents. Other more subtle changes in rhythm can also kill you through less obvious mechanisms.
Blood pressure (Bp) normally falls by 10 mmHg during sleep (green lines in figure), a phenomenon called dipping. Many patients with hypertension lose this dip (red lines in figure), and these patients have greater risk of heart disease and death over time. Loss of the dip increases the risk of heart disease above that of hypertension in which the dip is preserved. Clinical studies suggest that restoring this dipping profile may reduce protein in the urine, heart attacks, and death over the short term.
How can we demonstrate the dip? Continuous ambulatory blood pressure monitoring provides the answer. Patients wear an automatic Bp cuff that inflates every few minutes throughout the day and night. This important clinical tool shows the overall level of Bp control as well as its pattern.
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Restoring the dip is really pretty easy. The patient takes at least one Bp medication at bedtime. Recent work from Spain shows that long-term restoration of normal circadian Bp patterns is beneficial in patients with chronic kidney disease (CKD).
CKD patients often have hypertension that requires multiple medications to control; almost half of the patients in the study required 3 or more drugs for high blood pressure. The researchers first performed ambulatory monitoring in CKD patients, then randomly assigned them to take all of their Bp medications in the morning, or to take at least one drug at night. Approximately two-thirds of patients assigned to each group did not dip at night before the study began. Continuous ambulatory Bp monitoring was performed at least annually on every one of the 661 patients included in the final analysis. A number of events were analyzed over 5 years, including death from all causes and a variety of heart and vascular disease issues, including heart attack and stroke.
Giving at least one drug at bedtime restored the dip; 71% of the morning medication patients did not dip at study’s end, while bedtime dosing dropped nondippers to 41%. Bedtime dosing also produced more patients with controlled 24-hr Bp levels (56.5 vs. 45.2%). So bedtime dosing reduces overnight Bp for many years. Does it do anything to risk? Yes – bedtime dosing patients suffered all outcome events at 31% of the rate of patients taking all medications in the morning. The rate of major cardiovascular disease events, including heart attacks and strokes, dropped to 28% of the Morning group. In other words, something as simple as moving at least one Bp med to bedtime could reduce the risk of death and cardiovascular disease by more than two-thirds in CKD patients.
Of course, this study only examined 661 patients. They all had some degree of CKD, and the results may not apply to the vast majority of patients with high blood pressure. DO NOT change your own medications around without talking to your doctor, but DO talk to your doctor about bedtime dosing. It could save your life.
The real question, of course, is why dipping is so important. For that matter, why does Bp dip at night? Of course, science has yet to figure out why sleep happens!
We can try to figure out what makes Bp dip overnight. When Bp drops below a certain level, the sympathetic nervous system (an involuntary part of the brain and nerves that regulates basic body functions) increases activity to the heart and blood vessels to increase Bp and keep circulation going to vital organs. This phenomenon is called the baroreflex. During sleep the threshold Bp at which this activation occurs shifts down. In other words, Bp can drop lower and stay there longer without activating the baroreflex. While inactivity of muscles during sleep may contribute to this phenomenon, at least one study suggests that dipping is a more deliberate physiological process.
We may not yet know why, but people are clearly meant to sleep at night for their health and welfare, including heart health.
References:
Hermida, Ayala, Mojon, and Fernandez: Bedtime dosing of antihypertensive medications reduces cardiovascular risk in CKD. J American Society of Nephrol 22:2313-21, 2011. doi: 10.1681/ASN.2011040361