Sleeping less than six hours a night may increase cardiovascular risk

People who sleep less than six hours a night may be at increased risk of cardiovascular disease compared with those who sleep between seven and eight hours, suggests a new study published in the Journal of the American College of Cardiology. Poor quality sleep increases the risk of atherosclerosis -- plaque buildup in the arteries throughout the body -- according to the study.

"Cardiovascular disease is a major global problem, and we are preventing and treating it using several approaches, including pharmaceuticals, physical activity and diet. But this study emphasizes we have to include sleep as one of the weapons we use to fight heart disease -- a factor we are compromising every day," said senior study author José M. Ordovás, PhD, researcher at the Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC) in Madrid and director of nutrition and genomics at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University. "This is the first study to show that objectively measured sleep is independently associated with atherosclerosis throughout the body, not just in the heart."

Previous studies have shown that lack of sleep raises the risk of cardiovascular disease by increasing heart disease risk factors such as glucose levels, blood pressure, inflammation and obesity, he said.

The new study included 3,974 bank employees in Spain from the PESA CNIC- Santander Study, led by JACC editor-in-chief Valentin Fuster, MD, PhD, which uses imaging techniques to detect the prevalence and rate of progression of subclinical vascular lesions in a population with an average age of 46 years. All participants were without known heart disease and two-thirds were men. All participants wore an actigraph, a small device that continuously measures activity or movement, for seven days to measure their sleep. They were divided into four groups: those who slept less than six hours, those who slept six to seven hours, those who slept seven to eight hours and those who slept more than eight hours. The participants underwent 3D heart ultrasound and cardiac CT scans to look for heart disease.

The study found that when traditional risk factors for heart disease were considered, participants who slept less than six hours were 27 percent more likely to have atherosclerosis throughout the body compared with those who slept seven to eight hours. Similarly, those who had a poor quality of sleep were 34 percent more likely to have atherosclerosis compared with those who had a good quality of sleep. Quality of sleep was defined by how often a person woke during the night, and the frequency of movements during the sleep which reflect the sleep phases.

"It is important to realize that shorter sleep duration that is of good quality can overcome the detrimental effects of the shorter length," Fuster said.

The study also suggested sleeping more than eight hours a night may be associated with an increase in atherosclerosis. While the number of participants who slept more than eight hours was small, the study found women who slept more than eight hours a night had an increased risk of atherosclerosis.

Alcohol and caffeine consumption were higher in participants with short and disrupted sleep, the study found. "Many people think alcohol is a good inducer of sleep, but there's a rebound effect," Ordovás said. "If you drink alcohol, you may wake up after a short period of sleep and have a hard time getting back to sleep. And if you do get back to sleep, it's often a poor-quality sleep."

While some studies show drinking coffee can have positive effects on the heart, Ordovás said it can depend on how quickly a person metabolizes the coffee. "Depending on your genetics, if you metabolize coffee faster, it won't affect your sleep, but if you metabolize it slowly, caffeine can affect your sleep and increase the odds of cardiovascular disease," he said.

The new study is different from previous studies on sleep and heart health in several ways, Ordovás said. It is larger than many earlier studies and focused on a healthy population. Many previous studies have included people with sleep apnea or other health problems. While other studies have relied on questionnaires to determine how much sleep participants got, this study used actigraphs to obtain objective measures of sleep.

"What people report and what they do are often different," he said.

The study also used state-of-the-art 3D ultrasound to measure atherosclerosis throughout the body, not just in the heart.

In an editorial, Daniel J. Gottlieb, MD, MPH, and Deepak L. Bhatt, MD, MPH, from the VA Boston Healthcare System and Brigham and Women's Hospital Division of Sleep Medicine at Harvard Medical School and Brigham and Women's Hospital Heart and Vascular Center said further studies are needed to determine whether changing sleep behaviors will improve heart health.

"The potentially enormous impact of sleep deprivation and disruption on population health, reinforced by the present study, is ample justification for such trials, which are needed to place sleep with confidence alongside diet and exercise as a key pillar of a healthy lifestyle," they wrote.

Yoga, exercise fail to improve sleep in midlife women, study suggests

A new study indicates that yoga and aerobic exercise interventions did not significantly reduce objectively measured sleep disturbances among midlife women who were experiencing hot flashes.

Secondary analyses of a randomized controlled trial show that neither 12 weeks of yoga nor 12 weeks of aerobic exercise had a statistically significant effect on objective measures of sleep duration or sleep quality recorded by actigraphy. Although the women had no difficulty falling asleep, disturbed sleep was common at baseline and remained after each intervention, with women in all groups waking during the night for an average of more than 50 minutes.

According to the authors, previously published analyses of the same trial had found that the yoga and aerobic exercise interventions were associated with small but statistically significant improvements in subjective, self-reported sleep quality and insomnia severity.

"Our primary findings were that the two study interventions had no significant effects on objective sleep outcomes in midlife women with hot flashes. The main implication of this finding is that other behavior treatments with the potential for effectively improving sleep in this population should be examined," said lead author Diana Taibi Buchanan, associate professor of Bio-Behavioral Nursing and Health Informatics at the University of Washington in Seattle.

Study results are published in the Jan. 15 issue of the Journal of Clinical Sleep Medicine.

The authors analyzed data from the Menopause Strategies: Finding Lasting Answers for Symptoms and Health (MsFLASH) network. The study involved 186 late transition and postmenopausal women with hot flashes who were between 40 and 62 years of age. Study subjects had an average of 7.3 to 8 hot flashes per day. Participants were randomized to 12 weeks of yoga, supervised aerobic exercise, or usual activity.

Sleep measures were evaluated using wrist actigraphy, and bedtimes and rise times were determined primarily from the participants' sleep diaries. Mean sleep duration at baseline and after each intervention was less than the 7 or more hours of nightly sleep that is recommended by the American Academy of Sleep Medicine for optimal health in adults.

According to the authors, future research should explore other approaches for improving sleep quality in midlife women, such as cognitive behavioral therapy for insomnia.

Mystery of what sleep does to our brains may finally be solved

It is one of life’s great enigmas: why do we sleep? Now we have the best evidence yet of what sleep is for – allowing housekeeping processes to take place that stop our brains becoming overloaded with new memories.

All animals studied so far have been found to sleep, but the reason for their slumber has eluded us. When lab rats are deprived of sleep, they die within a month, and when people go for a few days without sleeping, they start to hallucinate and may have epileptic seizures.

One idea is that sleep helps us consolidate new memories, as people do better in tests if they get a chance to sleep after learning. We know that, while awake, fresh memories are recorded by reinforcing connections between brain cells, but the memory processes that take place while we sleep have remained unclear.

Support is growing for a theory that sleep evolved so that  connections in the brain can be pruned down during slumber, making room for fresh memories to form the next day. “Sleep is the price we pay for learning,” says Giulio Tononi of the University of Wisconsin-Madison, who developed the idea.

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Now we have the most direct evidence yet that he’s right. Tononi’s team measured the size of these connections or synapses in brain slices taken from mice. The synapses in samples taken at the end of a period of sleep were 18 per cent smaller than those in samples taken from before sleep, showing that the synapses between neurons are weakened during slumber.

A good night’s sleep

Tononi announced these findings at the Federation of European Neuroscience Societies meeting in Copenhagen, Denmark, last week. “The data was very solid and well documented,” says Maiken Nedergaard of the University of Rochester, who attended the conference.

“It’s an extremely elegant idea,” says Vladyslav Vyazovskiy of the University of Oxford

If the housekeeping theory is right, it would explain why, when we miss a night’s sleep, the next day we find it harder to concentrate and learn new information – we may have less capacity to encode new experiences. The finding suggests that, as well as it being important to get a good night’s sleep after learning something, we should also try to sleep well the night before.

 

It could also explain why, if our sleep is interrupted, we feel less refreshed the next day. There is some indirect evidence that deep, slow-wave sleep is best for pruning back synapses, and it takes time for our brains to reach this level of unconsciousness.

Waking refreshed

Previous evidence has also supported the housekeeping theory. For instance, EEG recordings show that the human brain is less electrically responsive at the start of the day – after a good night’s sleep – than at the end, suggesting that the connections may be weaker. And in rats, the levels of a molecule called the AMPA receptor – which is involved in the functioning of synapses – are lower at the start of their wake periods.

The latest brain-slice findings that synapses get smaller is the most direct evidence yet that the housekeeping theory is right, says Vyazovskiy. “Structural evidence is very important,” he says. “That’s much less affected by other confounding factors.”

Protecting what matters

Getting this data was a Herculean task, says Tononi. They collected tiny chunks of brain tissue, sliced it into ultrathin sections and used these to create 3D models of the brain tissue to identify the synapses. As there were nearly 7000 synapses, it took seven researchers four years.

The team did not know which mouse was which until last month, says Tononi, when they broke the identification code, and found their theory stood up.

“People had been working for years to count these things. You start having stress about whether it’s really possible for all these synapses to start getting fatter and then thin again,” says Tononi.

The team also discovered that some synapses seem to be protected – the biggest fifth stayed the same size. It’s as if the brain is preserving its most important memories, says Tononi. “You keep what matters.”

Read more: What does a memory in my brain look like?

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