The Doctor Weighs In

By Pat Salber, MD

We have known about the association between snoring and obesity for a long time. But we now know that sleep-disordered breathing (SBD) -- a sleep disturbance characterized by snoring and episodes of apnea or not breathing for periods of time -- is linked, independent of obesity, to insulin resistance, abnormal glucose metabolism, and Type 2 diabetes.

Sinziana Seicean, MD, MPH and colleagues published results of the Sleep Heart Health Study in the May 2008 issue of Diabetes Care. They studied 209 normal weight and 1,036 overweight/obese individuals who had a diagnosis of SDB, but did not have a diagnosis of diabetes. They found that SDB was associated with all of the manifestations of impaired glucose metabolism, including impaired fasting glucose, impaired glucose tolerance, and occult diabetes. The magnitude of the association between SDB and abnormal glucose metabolism was the same regardless of whether the individual was normal or overweight/obese.

This suggests that obesity is not the common cause of both insulin resistance and sleep-disordered breathing. Rather there appears to be an independent association between SDB and impaired glucose metabolism that is not explained by adiposity.

The authors suggest that the association of SDB with glucometabolic disturbances may relate to the “often-profound physiological stresses that occur overnight with sleep apnea.” They suggest that these stresses may transiently increase autonomic sympathetic activity, increase outpouring of the stress hormone, cortisol, and a decrease insulin sensitivity. Indeed, they point out that a human study of people with sleep apnea demonstrated improved insulin sensitivity after treatment of the SDB with continuous positive airway pressure (CPAP)

Why is this study important? Because it means that individuals with SDB who are normal weight may be at risk of impaired glucose metabolism. It also suggests that therapy aimed specifically at SDB and not just at obesity may be indicated to reverse that risk.

To learn if you are at risk of having SDB, answer the following questions based on the Berlin Questionnaire:

By Dov Michaeli MD, Ph.D

Our first in the series of debunking medical myths dealt with the maxim that you must drink 8 glasses of water a day. I hope you stopped drowning yourself in H 2 O. And if you survived this personal drought, here is another food related myth.

The turkey made me sleepy

Remember this truism? It is false. It’s not the turkey—it’s more likely the company!

· The main “evidence” repeated ad nauseam with great conviction is that turkey contains the amino acid tryptophan. This amino acid serves as the metabolic precursor of the familiar serotonin. And serotonin makes you feel happy and drowsy. Q.E.D.

Not so fast. Does pork make you drowsy? How about Swiss cheese? Both of these contain significantly more tryptophan that turkey does. In fact, all meat, including chicken and hamburgers, contain large amounts of tryptophan. Have you avoided driving after a stop at McDonald’s because you suddenly became sleepy. Besides, in order to provide enough tryptophan to enter the brain and form there enough serotonin to make you drowsy, you’d need to finish a couple of whole turkeys. Care to try it?

· What is true is that a large meal would tend to make you drowsy. But it has nothing to do with tryptophan or turkeys. What happens is that when a meal makes its way to the small intestine, where digestion takes place, blood is diverted to the GI tract, to better absorb the digested food in the form of sugars, triglycerides and amino acids, and deliver it to the appropriate organs. Since our total blood volume is constant, this diversion comes at the expense of blood flow to the brain and muscles. If the blood supply to the cardiac muscle is pretty low to begin with, additional reduction due to a heavy meal could be quite catastrophic. But in normal circumstances, the worst that can happen is that you will feel sleepy because of reduced blood flow to your brain.

So next time you sit down to a Thanksgiving, or Christmas, or a Seder meal—don’t fret. Eat to your heart’s content, and let the turkeys who worry about drowsiness leave their portions for you to have seconds and thirds.

Bon appetit!

My son Gil recently took a final exam in nursing  school after cramming the whole night. He did well, thank you. But when he told me about this feat of studiousness, I was wondering: how much is he going to retain one day after the test? I seem to recall from my college days that taking a test after an all-nighter was actually fraught with a lot of fuzzy thinking and faulty memory. Have you ever taken a test, and later asked yourself “how could I make such a stupid mistake”? Or “how could I forget that”?

Perchance to sleep

Sleep is an essential activity in our daily life. Since time immemorial sleep was associated with healing and healthfulness. Lack of sleep was associated with hallucinations and psychic torment. Just ask Lady Macbeth, walking all night, tormented by visions of blood and murder, longing for some blissful rest. Or the captives of state organs, subjected to sleep deprivation in order to wring some information or an admission out of them.

So why is sleep necessary? It has been the subject of lively debate among psychologists and neuroscientists for many years. Still, there is no answer. Some scientists even claimed that it actually is not necessary. One of my colleagues claimed that he never went to sleep for longer than an hour or two a night. But every time I visited him in his office at the university, I found him dozing at his desk. In fact, if sleep were not necessary, it would have been a colossal evolutionary waste; Evolution just doesn’t work that way.

Indeed, recent experiments convincingly demonstrated at least one function.

Brain waves

Human sleep is divided into REM, or rapid eye movement, and NREM, or non-REM, sleep. NREM is further divided into 4 stages, each characterized by typical electrical oscillations seen on an encephalogram, or EEG.

· REM sleep is characterized by theta waves, having oscillations of 4-8 Hz (Herz is a measure of frequency).

· Stage 1 is transitional between wakefulness and sleep, and is therefore characterized by a mixture of wave frequencies.

· Stage 2 is typified by spindle-shaped waves, of 12-14 Hz.

· Stage 3 and 4 are characterized by delta waves , of 1-4 Hz.

· Interwoven in the spindle waves and the delta waves pattern one can discern another oscillatory pattern : extremely slow, less than 1 Hz, wave pattern, called cortical slow oscillations, or slow-wave sleep.

Get smart

Marshall et al. did an ingenious experiment (Marshall et al. Nature, vol.444, pp.610-613, 2006). They wanted to know if any of these sleep phases were associated with consolidation of memory. So they let 13 volunteers memorize 46 word-pairs before going to sleep. Electrodes were then attached to their scalp, and fluctuating electrical potentials were then applied to half the group to induce cortical slow oscillations. The other half received sham stimulation.

The next morning the two groups were tested on the word-pairs they had memorized the night before. Results were quite remarkable. The group that had received the slow-wave stimulation performed better than the sham stimulation group. And they also performed better than they themselves had performed the night before. The effect was absolutely specific to slow-wave stimulation. No effect was shown when the subjects were stimulated with theta waves frequency of REM sleep. Timing of the stimulation was also important: the first 45 minutes of sleep enhanced recall, the last 45 minutes had no effect.

What did we learn?

· First, we now know for certain that sleep is important in consolidating memory.

· We also know that only certain brain waves (slow oscillating) are associated with memory consolidation.

· Finally, we know that if we want to do well on the test the next day, we’ve got to get a minimum of an hour’s sleep. This is when memories are getting embedded in our brain.

Can we enhance memory by artificial means?

Commercial claims notwithstanding (“learn a language while you sleep”), sleep-learning is a pipe dream; it doesn’t work. If you are willing to go to sleep with electrodes attached to your skull, you might be able to recall your Spanish lesson from the day before somewhat better. But those pesky electrodes will probably wake you up throughout the night, and you’ll feel like… (fill in your favorite expression) the next day.

Can this experiment point the way to a ‘memory drug’?

Unfortunately, not. Drugs work on chemicals in the body, not on electrical waves. We don’t know from this experiment which neurotransmitters are associated with the slow-wave oscillations. Acetylcholine, a known neurotransmitter associated with memory retention, has not been tested. Astonishing; they could have nailed it. Maybe they wanted to get another paper out of it. We’ll just have to wait.

Take home lesson

Gil, next time get some sleep; even an hour will ensure a better grade.

Dov Michaeli MD, Ph.D.