Researchers from the Sleep Heart Health Study (SHHS) report that the risk of stroke appears in men with mild sleep apnea and rises with the severity of sleep apnea. Men with moderate to severe sleep apnea were nearly three times more likely to have a stroke than men without sleep apnea or with mild sleep apnea. The risk from sleep apnea is independent of other risk factors such as weight, high blood pressure, race, smoking, and diabetes.

They also report for the first time a link between sleep apnea and increased risk of stroke in women. Obstructive Sleep Apnea Hypopnea and Incident Stroke: The Sleep Heart Health Study, was published online March 25 ahead of print in the American Journal of Respiratory and Critical Care Medicine.

Stroke is the second leading cause of death worldwide. “Although scientists have uncovered several risk factors for stroke — such as age, high blood pressure and atrial fibrillation, and diabetes — there are still many cases in which the cause or contributing factors are unknown, ” noted NHLBI Acting Director Susan B. Shurin, M.D. “This is the largest study to date to link sleep apnea with an increased risk of stroke. The time is right for researchers to study whether treating sleep apnea could prevent or delay stroke in some individuals.”

Conducted in nine medical centers across the United States, the SHHS is the largest and most comprehensive prospective, multi-center study on the risk of cardiovascular disease and other conditions related to sleep apnea. In the latest report, researchers studied stroke risk in 5,422 participants aged 40 years and older without a history of stroke. At the start of the study, participants performed a standard at-home sleep test, which determined whether they had sleep apnea and, if so, the severity of the sleep apnea.

Researchers followed the participants for an average of about nine years. They report that during the study, 193 participants had a stroke — 85 men (of 2,462 men enrolled) and 108 women (out of 2,960 enrolled).

After adjusting for several cardiovascular risk factors, the researchers found that the effect of sleep apnea on stroke risk was stronger in men than in women. In men, a progressive increase in stroke risk was observed as sleep apnea severity increased from mild levels to moderate to severe levels. In women, however, the increased risk of stroke was significant only with severe levels of sleep apnea.

The researchers suggest that the differences between men and women might be because men are more likely to develop sleep apnea at younger ages. Therefore, they tend to have untreated sleep apnea for longer periods of time than women. “It’s possible that the stroke risk is related to cumulative effects of sleep apnea adversely influencing health over many years,” said Susan Redline, M.D., MPH, professor of medicine, pediatrics, and epidemiology and biostatistics, at Case Western Reserve University in Cleveland and lead author of the paper.

“Our findings provide compelling evidence that obstructive sleep apnea is a risk factor for stroke, especially in men,” noted Redline. “Overall, the increased risk of stroke in men with sleep apnea is comparable to adding 10 years to a man’s age. Importantly, we found that increased stroke risk in men occurs even with relatively mild levels of sleep apnea.”

“Research on the effects of sleep apnea not only increases our understanding of how lapses of breathing during sleep affects our health and well being, but it can also provide important insight into how cardiovascular problems such as stroke and high blood pressure develop,” noted Michael J. Twery, Ph.D., director of the NIH National Center on Sleep Disorders Research, an office administered by the NHLBI.

The new results support earlier findings that have linked sleep apnea to stroke risk. SHHS researchers have also reported that untreated sleep apnea is associated with an increased risk of high blood pressure, heart attack, irregular heartbeats, heart failure, and death from any cause. Other studies have also linked untreated sleep apnea with overweight and obesity and diabetes. It is also linked to excessive daytime sleepiness, which lowers performance in the workplace and at school, and increases the risk of injuries and death from drowsy driving and other accidents.

More than 12 million American adults are believed to have sleep apnea, and most are not diagnosed or treated. Treatments to restore regular breathing during sleep include mouthpieces, surgery, and breathing devices, such as continuous positive airway pressure, or CPAP. In people who are overweight or obese, weight loss can also help.

These treatments can help improve breathing and reduce the severity of symptoms such as loud snoring and excessive daytime sleepiness, thereby improving sleep-related quality of life and performance at work or in school. Randomized clinical trials to test whether treating sleep apnea lowers the risk of stroke, other cardiovascular diseases, or death are needed.

“We now have abundant evidence that sleep apnea is associated with cardiovascular risk factors and diseases. The next logical step is to determine if treating sleep apnea can lower a person’s risk of these leading killers,” said Redline. “With stimulus funds, our research group is now developing the additional research and resources to begin answering this important question.”

Source: NIH News

Researchers at the University of California, San Francisco, have discovered the first gene involved in regulating the length of human sleep. The study, published recently in the journal Science, identified a genetic mutation that is associated with a short human sleep phenotype [1]. The finding may help scientists better understand the regulatory mechanisms of sleep and lead to treatments for a variety of sleep disorders.

Researchers identified a small extended family with two individuals who had lifelong shorter daily sleep times than normal individuals (self-reported average of 6.25 hours vs. 8.06 hours). DNA sequencing identified a point mutation in the gene DEC2 (Differentially expressed in chondrocytes protein 2) (chondrocytes are the only cells found in cartilage, the connective tissue within joints). In mice, DEC2 has been previously identified as a component of the mammalian circadian clock (the ~24-hour wake-sleep cycle), repressing the expression of other circadian clock genes [2]. In vitro tests showed that the human mutation reduced the repressive activity of DEC2.

To examine the effect of the mutation, scientists generated DEC2 transgenic mice (meaning a mouse with a segment of DNA that originated in a different species, in this case two copies of the human DEC2 gene, one containing the point mutation and one normal copy). Studies showed that these mice slept less compared to controls. To study sleep directly, electroencephalography (EEG) and electromyography (EMG) tests were performed. The results suggest that the DEC2 point mutation does not affect the depth of sleep. Rather, the sleep structure of mice containing the DEC2 point mutation appeared more fragmented than that of normal mice, particularly non-rapid eye movement (NREM) sleep (about 80% of sleep is spent in dreamless NREM sleep). Further studies found that mice with the mutation also recovered quicker from periods of sleep deprivation compared to normal mice.

Studies were then done in fruit-flies expressing either the normal mouse Dec2 gene or the mouse Dec2 gene containing the point mutation. Flies expressing the mouse Dec2 gene containing the point mutation showed significantly lower daytime sleeplike behavior compared with flies expressing the normal mouse Dec2 gene. Thus, the shortened sleep effect of the DEC2 point mutation was replicated in both mouse and fruit-flies.

What’s interesting about this study is that a genetic mutation can lead to a behavioral trait, not just an observable characteristic.

Seven in ten adults report not getting enough rest or sleep at least once in the past month. Over time, the body suffers from short term sleep deprivation. Not only does the lack of sleep increase your susceptibility to the common cold, chronic sleep disruptions can have serious consequences on cognition, mood and physical health.

How much is too little or too much sleep? There is no magic number. Different age groups need different amounts of sleep, but sleep needs are also individual. Generally speaking, research shows that most adults need 7-9 hours of sleep, while younger children need as much as 10-14 hours [3]. For more information on the importance of sleep as well as sleep-related problems, visit the National Sleep Foundation (NSF).

References

1. He et al. The transcriptional repressor DEC2 regulates sleep length in mammals. Science. 2009 Aug 14;325(5942):866-70. DOI: 10.1126/science.1174443
   View abstract
2. Honma et al. Dec1 and Dec2 are regulators of the mammalian molecular clock. Nature. 2002 Oct 24;419(6909):841-4.
   View abstract
3. How Much Sleep Do We Really Need? National Sleep Foundation. Accessed 2009 Sept 1.