Snooze Your Way to Heart Health
Studies find heart disease is linked to lack of sleep
There's nothing like a good night's sleep to help you feel refreshed, lift your spirits and make you productive. But sleep is also important to health: studies have consistently found that lack of sleep is associated with an increased risk of obesity and heart disease.
Now, new research finds that it's not just the quantity of sleep but also the quality of sleep that impacts health. In a recent issue of the journal Hypertension, Susan Redline, MD, a sleep investigator at Beth Israel Deaconess Medical Center, and Peter C. Farrell, Professor of Sleep Medicine at Harvard Medical School, describe findings from a new study that show that men who get the least amount of "deep sleep" each night have a higher risk of developing high blood pressure.
Your research looked at how sleep - or lack of sleep - affects men's blood pressure. Can you tell us more about this?
We've actually had ample evidence that chronic sleep disorders and lack of sleep are linked to a greater risk of heart disease. In this latest study, we were looking specifically at a person's quality of sleep and quantified the amount of deep sleep to determine how that might influence blood pressure.
What is deep sleep?
What we refer to as deep sleep is technically called slow-wave sleep or delta sleep. It's the period of about 90 minutes to two hours when the brain's electrical activity shows greater synchronization - the brain's electrical waves are deeper and slower. Heart rate, blood pressure and adrenaline levels also drop in this stage of sleep.
How was your study conducted?
We followed 784 healthy men (average age of 75) recruited from six sites across the U.S. for three and a half years. A standardized, in-home sleep study was conducted at the beginning of the study. Our research center received and analyzed all of the sleep data and assessed the amount and type of sleep each man experienced and also determined whether there was evidence of sleep apnea or periodic limb movements. The participants had no signs of hypertension at the start of the study. Over time, we assessed the health of the men in the study and measured the change in their blood pressure.
What were the results?
Of the 784 men initially free of high blood pressure, we found that 243 developed high blood pressure (measuring greater than 120/80 or needing blood-pressure medication) after 3.4 years of follow-up. Further analysis showed that these same men were distinguished by the very low levels of deep sleep they had when first studied - specifically, those who were at highest risk for developing high blood pressure were those who had not spent more than four percent of their total sleep time in deep sleep. This is significantly less than the 25 percent of slow-wave sleep that the average middle-aged adult should expect. In addition, this finding was seen even after considering other variables that may influence the development of high blood pressure, such as weight and age, and also was seen after considering other sleep problems.
Why do you think this might be happening?
For one thing, normally blood pressure drops during deep sleep. So, men with less deep sleep may not have experienced a normal "dip" in blood pressure, which may over time cause damage to blood vessels and increase risk of hypertension occurring during the day. We also know that the areas of the brain that regulate sleep patterns engage in a lot of "cross-talk" with areas of the brain that release hormones and other signals that help influence blood pressure. If these parts of the brain aren't entering slow-wave sleep, then various brain signals that impact blood pressure may be disrupted.
How do you know if you're experiencing slow-wave sleep at night?
The only definitive way to know this is by undergoing an overnight sleep study. However, a general rule of thumb is that you should wake up feeling well rested after seven to eight hours of sleep; if you still feel tired or sluggish or if you have trouble sleeping, you may not be getting adequate slow-wave sleep and should talk with your doctor.
Posted October 2011