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.

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.

Sleep problems common on simulated space mission

Here is an article about an experiment done to simulate space travel. Astronauts were confined to a pressurized spacecraft in Moscow for 520 days straight. Their sleep was monitored with an actigraph, a type of accelerometer. After a month, some of the crew members began to have sleep problems. It seems that one of the issues is that the low light levels on the spacecraft are not strong enough to simulate the day-night cycle we experience daily. Since our brain's clock depends on light to keep our rhythms regular, exposure to stronger light sources on the spaceship may help in actual space flight.

Neuroscientist advises NASA about importance of proper lighting to sleep

This article features a neuroscientist who is advising NASA about replacing its outdated lighting on spacecraft with high tech adjustable lights. This may improve astronauts sleep quality, since light affects sleep and other aspects of our daily functioning.

New Findings About Our Biological Clock

This article describes some interesting findings about how our biological clock may control how when we wake and when we sleep.

Circadian Rhythm, Gender, and Insomnia

There was a study done last month published in the Proceedings of the National Academy of Sciences about the differences in circadian rhythm between men and women. Our circadian rhythm is the 24 hour cycle that controls many of our bodily functions, including when we sleep.

For this study, the researchers observed the natural circadian cycles of men and women in a controlled sleep lab over 2 to 6 weeks. The results showed individuals circadian rhythms ranged from about 23.5 to 24.5 hours, and was unaffected by age. The circadian clock of women averaged about 6 minutes less than the men, and the women were 2.5 times more likely than the men to have cycles shorter than 24 hours.

The researchers do not know why women's circadian rhythm would be shorter than men's, but it could be related to female estrogen levels.

A circadian rhythm that is short could explain in part why some women may have difficulty maintaining sleep and early morning awakening. It also could mean that women might get sleepy earlier than men. Unfortunately, there isn't anything that can be done to change the length of your circadian rhythm. Practicing good sleep hygiene and listening to your body will help you sleep better.

Sleep-Wake Behavior and Chronic Fatigue Syndrome

In the journal Sleep, K Rahman et al published a study that assessed the relationship of sleep-wake behavior and chronic fatigue syndrome (CFS). Patients with CFS usually report unrefreshing and restless sleep. To date, scientists have not been able to figure out what makes CFS patients experience the subjective sleep disturbances. In addition, sleep studies have not confirmed objective sleep disturbances in patients with CFS, meaning that there is no evidence that CFS results from a sleep disorder. Researchers do feel that changes in sleep patterns and activity levels can maintain the symptoms of CFS.

This study attempted to determine if circadian rhythm disturbances could be responsible for the fatigue and unrefreshing sleep reported in CFS patients. The results, though, showed no differences in recordings of sleep pattern, sleep duration, daytime activity, or cortisol secretion (a marker of circadian rhythm) between CFS patients and control subjects. The authors concluded that a disruption in circadian rhythm is not associated with CFS.

Interestingly, despite no differences in objective sleep measures, all of the CFS patients in this study reported poor sleep quality. One finding that was different between CFS patients and the control subjects was a loss of vagal modulation of heart rate in CFS patients, which indicates a state of increased sympathetic arousal. Think of vagal modulation (or parasympathetic system) as the brakes of a car and the sympathetic system as the accelerator - thus, in CFS patients, the brakes do not work and the accelerator is going unchecked. There are studies that suggest that normal vagal modulation is needed to make sleep restorative. Therefore, the decrease in vagal modulation could be a biological explanation for the poor sleep quality reported by CFS patients.

It would be interesting to see if medications that increase vagal tone have been reported to make sleep more refreshing. If anyone knows of such reports, put it in a comment here.