Friday, July 1, 2016

Sleep restriction and athletic performance

I used to run long distance back in my salad (younger) days. I read books and magazines about running and running performance. I remember reading something back in the 1980's about how sleep deprivation did not affect running performance.

However, here is an article about recent research showing small reductions in performance of elite cyclists with voluntary sleep restriction to 4 hours per night for 3 days. The researchers measured energy expenditure, maximal aerobic power, and time to exhaustion. However, I don't see any data about actual cycling performance such as time to complete a course, etc. Therefore, I am not sure if sleep restriction really impacts elite cyclists. I know that not getting enough sleep lowered my motivation to run the next day!

Wednesday, May 4, 2016

High blood pressure and insomnia

Insomnia refers to an inability to sleep the desired amount despite adequate allotted time in bed. People with insomnia often misperceive their sleep duration. Research studies have linked chronic insomnia with increased risk of high blood pressure (HTN). Sleeping less than 6 hours is considered being a "short sleeper" and is also associated with HTN.

This study looked at the association between short sleepers with insomnia and HTN. Participants underwent two consecutive in-lab sleep studies to objectively monitor sleep duration. They also had the participants record their subjective sleep duration with a sleep diary. Results showed that insomnia with objectively-measured sleep duration less than 6 hours was associated with increased risk (Odds Ratio 3.59) for HTN. This finding was independent of the following confounders: age, gender, race, body-mass index, frequency of sleep aid use, sleep apnea severity, daytime sleepiness, diabetes, high cholesterol, depression, alcohol use, tobacco use, or caffeine consumption.

The authors concluded that the results provide further support for measuring sleep duration objectively, rather than subjectively for those patients with chronic insomnia. This means the authors are advocating for sleep studies in the evaluation of chronic insomnia to help determine morbidity risks associated with the insomnia.

Wednesday, April 20, 2016

Sleep duration and sleep hygiene differences in homeschooled vs public / private school students

Adolescents tend to be a sleep-deprived bunch. I know I was when I was in high school. Adolescents tend to stay up late, in part because of a biological shift in circadian rhythm. Plus, high school starts earliest, which deprives adolescents of sleep as well. On the weekends, some adolescents try to make up for lost sleep by sleeping in, but this does not erase 5 days of partial sleep deprivation. Advocates have requested later school start times to help, but this is not done in most schools.

This study is about kids that are homeschooled. In this population, these kids can sleep in later, offsetting the daytime sleepiness from sleep deprivation as seen in public / private school kids. Also, kids that are homeschooled have a parent with them more often and thus may have better sleep hygiene than public / private school kids - meaning less TV / screen time in bed, less caffeine in evening, etc.

Study participants were surveyed about their sleep patterns and sleep hygiene via internet. Mean age of the sample was 13.6 years old. The results showed that kids in public / private school went to bed somewhat earlier on weekdays, but got up much earlier, resulting in 49 less minutes of sleep than homeschooled kids. Also, public/private school kids tended to sleep in more on weekends than homeschooled children. Using the National Sleep Foundation’s categories of “optimal sleep” (>9 hours) 28.2% of public/private school students obtained optimal sleep on weekday nights compared to 58.0% of homeschooled students. Public/private school kids tended to have "poorer" sleep hygiene than homeschooled kids.

The authors concluded that later school start times would allow private / public school kids to get more sleep.

Wednesday, March 23, 2016

Nap duration and sleep inertia

Napping can help shift workers maintain alertness, but a nap that is too long can result in what's called 'sleep inertia'-the brief period of time of reduced alertness and impaired cognitive performance experienced immediately after waking from the nap. Minimizing sleep inertia may improve a worker's performance on the job. Some studies have shown that a 10 minute nap results in less sleep inertia than a 30 minute nap, possibly because the napper wakes from a lighter stage of sleep during the 10 minute nap. With a 30 minute nap, the napper is more likely to wake from slow wave sleep, which is the deepest level of sleep.

Relatively few studies on sleep inertia have been done where the night shift worker takes a nap during their work shift. This study examined the cognitive performance and subjective sleepiness immediately following either a 10-minute or 30-minute nap at 4 am. The researchers studied young, healthy volunteers in a research lab. Participants slept normally for the first night. The second night they were kept awake the entire night. One third were allowed no nap, another third were allowed the 10 minute nap, and the remaining third allowed the 30 minute nap. The participants did a battery of cognitive performance tests and subjective rating scales prior to the nap and 4 times during the first hour after the nap.

Remembering this is a small study, the results showed that 8/10 participants woke up in a lighter stage of sleep after a 10 minute nap. Also, 8/10 participants woke from slow wave sleep after the 30 minute nap. 3/10 participants entered into slow wave sleep in the 10 minute nap compared to 10/10 participants in the 30 minute nap. In other words, the longer nap allowed enough time for the participants to progress to the deepest level of sleep.

Regarding the post-nap testing, the 10 minute nap was associated with minimal sleep inertia and was helpful in slowing the performance decline seen in the group that took no nap at all. The 30 minute nap was associated with substantial sleep inertia. In addition, even though there was objective proof of reduced cognitive performance following the 30 minute nap, those participants rated their sleepiness as better after the longer nap. This means that the participant who napped 30 minutes overstated their ability to perform cognitive tasks during the hour following that nap. The study authors suggest that if night shift workers have to perform immediately post-nap, that the worker take only a 10 minute nap rather than a longer nap.

Wednesday, March 9, 2016

Sleep deprivation and false convictions

Here is a study that attempted to link sleep deprivation to "false confessions." I don't have access to the entire study, only the summary article referenced above. Researchers studied 88 participants in a research lab, where some were sleep deprived for 24 hours and others slept 8 hours. The researchers had the participants take a series of computerized tests and were told not to press the 'Esc' key as that would delete data. At the end of the study, the participants were asked to sign a statement stating they had pressed the 'Esc' key. Results showed that 50% of the sleep-deprived people vs only 18% of the well-rested people signed the 'false confession.'

I'm not sure this demonstrates that sleep-deprivation leads to more false confessions. It may be that sleep-deprivation causes individuals to pay less attention to what they are reading. Signing something at the end of a research study has far less implications than signing a confession statement where you are being accused of a crime you didn't commit. In the latter instances, adrenaline may offset the affects of any sleep deprivation.

Wednesday, February 24, 2016

Bedtime and metabolic health

Research has shown an association between shift work and metabolic health. Specifically, shift workers are prone to obesity and type 2 diabetes. However, there is less research data about a variable sleep schedule that is not related to shift work. I'm referring to individuals who have one bedtime during the work week but a later bedtime on the weekends. This study researched the effects of going to bed later on weekends and obesity as well as metabolic health. They studied all women with a mean age of 52 years. The researchers collected information annually on sleep times and duration with a sleep diary for about 5 years. They recorded the patient's weight and drew blood to check for insulin resistance (a marker for pre-diabetes). The results showed that a greater variability in bedtime and going to bed early was associated with an elevated body mass index. Interestingly, the mean bedtime and going to bed later were not related to body mass index. However, variability in bedtime and going to bed later on the weekends was associated with an increased rate of insulin resistance, even after adjusting for factors including sleep duration.

The authors speculate on the reason why later weekend bedtimes could contribute to insulin resistance. One possibility is that there is more exposure to light at night which could alter melatonin and possibly increased consumption of food. However there was no significant increase in weight over time despite later bedtime. It may be that people who go to bed later on weekends are eating more simple carbs but don't necessarily gain weight. Increased carb intake could be contributing to the insulin resistance. More studies will need to be done to see how clinically important these effects are, as the statistical differences were real, but small.

Wednesday, February 17, 2016

UNM hospital room lighting

Light affects sleep - especially our circadian rhythm, or the timing of our sleep. The University of New Mexico has built a hospital room with special lighting equipment that researchers will be able use to study the circadian rhythm of humans. The researchers will also be able to study how light effects certain neurological and psychiatric disorders such as delirium after surgery, depression, dementia, and psychosis that develops in ICU patients. Apparently, the lighting is "smart" in that it can alert a nurse that a patient has fallen, but the lighting uses no cameras! Not sure how that works, but it sounds pretty cool to me.