Some problems are so ponderous they hang about the neck dragging down one's energy and vitality like an anchor. When answers to such problems are
evasive, one of the best pieces of advice to "sleep on it." For the majority of Americans, one of the most burdensome problems is weight, as two -
thirds of the U.S. population is either overweight or obese.
The science of fat loss is growing as quickly as waistlines, and rather than clarifying the issue, new discoveries are actually revealing a complex
interplay between and among a myriad of seemingly unrelated factors. Recently published research illustrates one such example - the relationship
between sleep and obesity.
COMMON SENSE vs. REALITY
Common sense dictates that energetic, active people, those who burn the candle at both ends, are destined to be slender. It's easy to picture night
owls snacking on cheese, crackers and Mountain Dew late at night in the desperate attempt to "put some meat on them bones" as they surf furiously
across the Web, chuckle with Jay Leno and blast through bandwidth in Halo 2 parties.
Ironically, evidence is building that the exact opposite is closer to the truth. It appears counting sheep may be as important as cardio and cutting
calories in the quest to reduce body- weight and fat.
The first hints that sleeping more may be an important aspect of weight management came from sleep surveys following the sleep habits of Americans.
Comparing data from the 1960's to today, it's clear that people are sleeping significantly less now than they were four decades ago. In fact, the average
number of hours of sleep dropped from nearly nine hours to less than seven hours a night for survey respondents.
Sleep researchers noted this trend in sleep deficit occurred during a period when bodyweight (measured as body mass index; BMI) was steadily rising.
This trend was confirmed in large population studies, but such studies can only describe associations, not causes. A famous example is given in
statistics and law classes: It has been shown that as sales of ice cream increase, deaths by drowning also go up. Eating ice cream does not cause
people to drown, so does that mean the figures are wrong? No, it means eating ice cream and drowning are associated, they tend to happen at the same
time, but one does not cause the other. The reason drowning deaths increase as more ice cream is eaten is that both occur during the summer.
Warm weather increases both ice cream consumption and swimming coincidentally, so the two activities are associated in a weather-related fashion, not
by one causing the other.
Conclusions from the population studies are limited in the same manner. During the last 40 years, people have tended to sleep less and gain weight.
It's impossible from this set of data to say one causes the other, as factors common to both could be linking weight gain to sleep loss. It could be
argued that people have a lower requirement for sleep as they are trending away from physically demanding jobs to sedentary positions; entertainment
choices have expanded keeping people glued to television screens and video monitors late at night; or eating habits have changed with late night meals
and snacking occurring later. These are just a few examples of possible associations between sleep loss and weight gain that cannot be explained by a
simple population study.
The greatest value of associations is to lead investigators to explore new areas of research. Given the growing demand obesity and weight related
problems place on society, financial and health resources, understanding the influence of sleep loss on weight gain could translate to correcting
two of the most prevalent health problems and quality of life issues. Researchers have answered the call and recently published a number of studies
that offer some insight regarding the relationship between sleep loss and weight gain, including suggestions as to how one affects the other.
SLEEP PATTERNS and HORMONE RELEASE
Sleep is not just a matter of being unconscious; at least five distinct phases of sleep have been identified. It has been shown that during sleep,
certain hormones increase and others decrease. These fluctuations in hormone levels occur as part of a natural wave-like pattern called the circadian
rhythm. When sleep patterns are disrupted, or if sleep is denied or restricted, the hormone release pattern is also disrupted.
Changes in hormone levels or patterns affect body physiology and behavior. This is particularly true in animals, which have been subjected to forced
sleep deprivation. When rats are denied sleep, they eat more and gain weight; in part, due to an increase in an appetite-stimulating neurotransmitters
called orexins. Conversely, if rats are deprived of food, they tend to sleep less, as the same orexins are involved in wakeful. So, the same neurotransmitter
family is involved in both wakefulness and stimulating appetite in the rat. Whenever either condition is present (sleep denial or starvation), both
behaviors are stimulated by the orexins eating and staying awake.
Humans are more complicated than rats, as many different factors influence behavior Not only are there hormones that affect sleep or appetite; social
conditions, artificial environments (24-hour lights, audio- visual stimulation), prescription and illicit drug use, and psychological emotional disorders
also affect these states, to name several. However, researchers are limited in that they must restrict experiments to focus on one relationship.
There are certain hormones that strongly influence appetite, such as leptin and ghrelin. Leptin is a hormone produced primarily by fat cells that signal
the energy state; when there is plenty of energy (food) available, leptin levels are high and sup- press the appetite. Ghrelin is a hormone produced by
the stomach that stimulates hunger and appetite; ghrelin is reduced by meals. When the stomach is empty, ghrelin is released in high levels and since the
body senses the energy (food) levels are low, leptin levels drop. This condition increases hunger. Eating a meal suppresses ghrelin and leptin is released
in response to the rise in available energy, thereby suppressing hunger.
Researchers have investigated the effect of sleep restriction on hunger and appetite, as compared to sleep extension (sleeping less versus sleeping longer),
attempting to explain any differences by looking at certain hormones known to have an effect on hunger. Two interesting studies were recently published by a
team led by Dr Eve van Cauter that offer some insight into the sleep-hunger relation- ship. In the first study, healthy, adult males were studied under
controlled conditions with regulated carb intake and activity. The subjects were studied under two different conditions- six days of sleeping only four
hours (total sleep time three hours, 49 minutes) a day versus sleeping 12 hours (total sleep time nine hours, three minutes) per day.
Leptin was significantly affected by the changes in sleep duration. Six days of being allowed only four hours of sleep caused a 19 percent reduction in mean
leptin levels, consistent with earlier studies. This degree of leptin decrease is similar to that noted when subjects are placed on a 900-calorie-per-day
deficit diet. Thus, relative to the leptin levels, sleeping four hours per day, as compared to nine hours of actual sleep, may cause one to be as hungry as
if he were consuming 900 calories fewer than maintenance.
Leptin is not the only hormone affected by a six-day period of sleep loss. Cortisol levels rose during the sleep restriction phase. Cortisol is known to
stimulate appetite and also break down muscle, two effects that would be very detrimental to a bodybuilder). TSH (thyroid stimulating hormone) a hormone
released by the pituitary gland to control thyroid hormone output and metabolism is reduced during sleep deprivation. A reduction in TSH may decrease the
metabolic rate, meaning that subjects would burn fewer calories.
Glucose tolerance, which is a measure of how well the body handles sugar, is based upon the actions of the hormone insulin. When the body is sensitive to
insulin, it only takes a small amount to shuffle sugar into the working muscles and tissues. If the body becomes resistant to insulin, it requires more of
the hormones to handle sugar, and fat storage may be promoted. Glucose tolerance is also affected by sleep duration, as the subjects demonstrated impaired
glucose tolerance during the sleep deprivation phase. Insulin is also capable of stimulating hunger.
Sympathovagal balance is a term that refers to the ratio of activity of the two major branches of the nervous system, excitatory versus relaxation. Sympathetic
or excitatory activity is determined primarily by the neunorepinephrine and the hormone adrenalin; vagal activity refers to the relaxation effect of the vagus
nerve (via the neurotransmitter acetylcholine) on heart rate and other vital signs. Whon sympathovagal balance is increased, it indicates the body is stimulated
similar to being in a minor adrenalin rush. Sleep deprivation increases sympathovagal balance, which indicates the nervous system is more excited, less relaxed,
or both. This was an interesting finding, as changes in sympathovagal balance can affect hunger-related hormones independent of sleep loss.
A second study was published using data from the same group of subjects. In this study, the relationship between sleep duration and the leptin-ghrelin ratio
were examined, Once again, it was noted that leptin levels decreased 19 percent during sleep deprivation. In contrast, ghrelin levels increased during sleep
deprivation by 28 percent. The subjects were asked how hungry they were and what foods sounded most appealing to them during this time, Not surprisingly,
subjects were much hungrier under conditions of sleep loss, They also voiced a preference for high-calorie, high-carbohydrate foods. Simultaneously dropping
leptin and raising ghrelin caused hunger and appetite to increase 23 percent and 24 percent, respectively.
It was suggested that the fall in leptin may be due in part to the increased sympathovagal balance, as excitatory drugs which stimulate the sympathic nervous
system reduce leptin levels. The vagus nerve (which dictates vagal tone) has been shown to suppress ghrelin, the hunger hormone of the stomach. An increased
sympatho-vagal balance may indicate that the vagus nerve is less active, removing any inhibitory effect on ghrelin release. This would be consistent the increase
in ghrelin levels noted during the sleep loss phase.
SAY GOODNIGHT ALREADY!
Americans are part of a driven society that values activity and demands entertainment. Due to the many influences that have become part of everyday life, along
with the related demands on our time, we are steadily losing sleep. Since the 1960's, Americans have given up, on average, nearly two hours of sleep each night.
This schedule places a great percentage of the population at risk for a chronic sleep deficit, which may result in physiological changes that affect our health.
Sleep habits have been shown to affect hormones that directly impact levels of hunger. Studies have now shown a direct relationship between chronic sleep loss and
changes in leptin, ghrelin and other factors that control the appetite centers of the brain and the body's ability to use and store calories. Chronic sleep loss is
associated with changes that would promote increased calorie consumption and may lead to weight gain.
It's still premature at this point to prescribe eight or nine hours of sleep per day as part of a weight loss program, but the evidence presented to date is
convincing that some relation- ship exists between chronic sleep habits and weight problems for the general population. Considering sleep is simple, free and
safe, there's no reason to avoid improving sleep habits. Athletes have long been aware that insufficient sleep can adversely affect competitive performance, but
now there is good reason for all people to turn off Jay Leno, say goodnight to the kids and pets and get a little extra shut-eye.