Normal blood pressure is anything under 120/80, and when readings creep higher, it’s usually a sign that lifestyle changes are needed. Otherwise, blood pressure will continue to increase and eventually produce harmful changes in the structure of the heart and blood vessels. Blood pressure that’s consistently elevated is a silent killer. It rarely produces symptoms unless it is severe, yet is a major risk factor for heart attack, stroke and kidney failure.
Poor Sleep Is Risk
The effect of sleep on blood pressure–or any aspect of health–has not been well studied, but that is changing. A 2006 study published in Hypertension found that, at least among middle-aged adults, lack of sleep increased the risk of hypertension (high blood pressure). Using data from 4,810 subjects in the National Health and Nutrition Examination Study (NHANES I), researchers found that persons who slept five hours or less a night tended to have higher heart rate and blood pressure than other subjects, setting them up for chronic health problems.
About 24 percent of sleep-deprived middle-aged subjects (between ages 32 and 59) developed hypertension over a 10-year period compared to 12 percent of subjects who got seven to eight hours of sleep. The same result was not found for older subjects. The researchers stressed that the results do not prove that the subjects’ sleep habits affected their blood pressure. But they do illustrate the need for more study.
These subjects exercised less and were more likely than other subjects to be overweight and to have diabetes or depression–all factors that can influence blood pressure. Other studies have indicated that lack of sleep tends to increase appetite and make cells less sensitive to insulin. Sleep is also a time when the heart has a chance to slow down. Under normal conditions, both heart rate and blood pressure drop for an extended period during sleep. As early as 1996, researchers found that subjects tended to have higher than usual blood pressure and heart rate the day after a night with insufficient sleep. The authors speculated that this might be a result of increased activity of the sympathetic nervous system related to lack of sleep.
One major reason that many Americans have inadequate sleep–often without their knowledge–is sleep disordered breathing or sleep apnea. The person with sleep apnea stops breathing for 10 seconds or longer hundreds of times a night, episodes that typically end with a choking, snorting sound.
A study of 140 children using ambulatory or portable blood pressure monitors worn 24 hours a day found that those with sleep-disordered breathing had significantly higher blood pressure and signs of thickening of the left ventricular wall of the heart–a structural change often associated with hypertension that can lead to serious heart problems including heart failure.
One reason heart attacks tend to occur during the morning hours may be that most individuals experience a steady increase of blood pressure at this time following a night of sleep. The children with sleep disordered breathing in this study also had higher than normal morning surges of blood pressure.
Treatment of sleep apnea ordinarily involves nighttime use of a mask that provides continuous positive airway pressure (CPAP). Another study found that use of CPAP not only improved sleep in subjects but lowered their blood pressure.
Dippers and Non-Dippers
The normal daily pattern is for blood pressure to “dip” or decline by 10 to 20 mmHg each night between 8 p.m. and 2 a.m. and then start rising throughout the early morning. The rise is in response to increased production of hormones that cause a tightening of blood vessels throughout the body.
Some individuals, for reasons that are not entirely understood, are “non-dippers.” Their blood pressure remains elevated, or may even rise, throughout the night. Non-dippers have an increased risk of blood-pressure-related damage to the heart, brain and kidneys. But persons who have an extreme dip (a decrease of 20 percent or more) during the night may also be at risk of problems related to the morning surge of blood pressure. An extreme surge of blood pressure in the morning hours is a strong predictor of stroke.
African Americans are more likely to be non-dippers, and they have a risk of stroke doubled that of white Americans. One study concluded that non-dipping was a greater factor than the early morning surge in the increased incidence of stroke. A majority of persons with hypertension are also salt sensitive, and these persons are also more likely to be non-dippers. A non-dipper who goes on a low sodium diet or starts medical treatment for hypertension usually reverses the pattern and becomes a dipper.
Most of us, of course, have no clue what our blood pressure is during sleeping hours, and the only way of finding out is through use of an ambulatory blood pressure monitor, which may not be needed. A more important strategy is focusing on what you can control: getting a good night’s sleep–seven to eight hours–every night, lowering your salt intake and taking medications your doctor prescribes for hypertension.
Michelle Herbert Thomas, PharmD, CDE
Clinical Director
Richmond Apothecaries, Inc.
