If you are an older man and are not getting enough slow wave sleep, a state of dreamless deep sleep, your risk of developing hypertension (high blood pressure) is considerably greater, researchers from Harvard Medical School in Boston, Mass., USA reported in Hypertension: Journal of the American Heart Association. The authors emphasized that quality sleep is as vital to health as exercise and diet.
Slow wave sleep, also referred to as SWS, is Stage 3 and 4 non-REM (non-rapid eye movement) sleep. It is characterized by brain wave patterns with a frequency of less than 4 Hz and peak-to-peak amplitude of 75 microV. It is one of the deeper stages of sleep. Individuals in this stage of sleep are more difficult to wake up.
Reduced SWS is a strong predictor for developing hypertension in older men, the authors wrote. Older men with the lowest SWS levels had an 80% higher risk of developing hypertension compared to men of the same age without reduced SWS.
Susan Redline, M.D. and Professor Peter C. Farrell said:
"Our study shows for the first time that poor quality sleep, reflected by reduced slow wave sleep, puts individuals at significantly increased risk of developing high blood pressure, and that this effect appears to be independent of the influence of breathing pauses during sleep."
Over the 3.4 years of the study, the researchers found that the men who spent less than 4% of their sleep time in SWS had a considerably greater chance of developing hypertension.
Reduced SWS among men generally occurred in those who slept for shorter times and woke up more often during the night, or had severe sleep apnea, compared to those with higher SWS levels.
However, of all the sleep quality measures the investigators examined, reduced SWS had the strongest link to hypertension risk. This association persisted even after other aspects of sleep quality were taken into account. The impact of SWS was independent of obesity, and continued to be observed even after considering the effects of obesity.
The scientists evaluated sleep characteristics associated to hypertension in 784 older males with an average age of 75, they were all Caucasian and none of them had high blood pressure. They were monitored at home using polysomnography. Their brain wave activity was measured so that their periods of REM and non-REM sleep could be registered.
The investigators assessed a wide range of measurements of sleep disturbances using a central Sleep Reading Center directed by Redline. Participants' time in each sleep state, frequency of breathing disturbances, how often they woke up and night, and their sleep duration were all measured.
The participants were all healthy and lived in one of six communities - what the authors described as a nationally representative sample of men.
High blood pressure is more common among older people than younger ones. Older individuals also tend to have more sleep disorders and sleep quality problems compared to younger people. Obesity is also linked to hypertension, the authors wrote.
"Although women were not included in this study, it's quite likely that those who have lower levels of slow wave sleep for any number of reasons may also have an increased risk of developing high blood pressure."
The researchers explained that SWS has been found to have an impact on memory and learning, as well as metabolism and diabetes.
"People should recognize that sleep, diet and physical activity are critical to health, including heart health and optimal blood pressure control. Although the elderly often have poor sleep, our study shows that such a finding is not benign. Poor sleep may be a powerful predictor for adverse health outcomes. Initiatives to improve sleep may provide novel approaches for reducing hypertension burden."
Written by Christian Nordqvist