Lack of sleep raises the risk of diabetes in the elderly

By FIONA MACRAE

Poor quality sleep could raise the risk of diabetes in the elderly, a study suggests.

Research shows that interruption of deep sleep has a dramatic effect on the body's metabolism and the conversion of sugar into energy, heightening the risk of diabetes.

Just three nights of disrupted sleep can have the same effect on the body's ability to control sugar levels as putting on more than two stone in weight, the study found.

The finding is likely to be particularly relevant to the elderly, whose sleep is usually shorter and of poorer quality than that of younger people.

In addition, the risk of type-2 diabetes, the most common form of the disease, rises with age.

The U.S. researchers said it would be wise for older people to take measures to improve their sleep quality.

The University of Chicago study looked at the effect of sleep quality on the body's ability to produce insulin, the hormone needed to control blood glucose or sugar levels.

Nine healthy young men and women were monitored during five nights of sleep.

During the first two nights, they were allowed to sleep normally. After that, their sleep was regularly disrupted by noises calculated to be loud enough to draw them out of deep sleep without fully waking them.

The disruption to deep sleep was equivalent to that seen during the ageing process, with the young volunteers experiencing a quality of sleep more usually seen in people in their 60s.

After normal sleep and interrupted sleep the volunteers were given injections of glucose and their blood was sampled to measure how well the sudden influx of sugar was being controlled.

Analysis showed that sleep quality had a big effect on the body's ability to use insulin to control blood sugar levels, with levels rising by an alarming 23 per cent after just three nights of interrupted sleep.

Such an inability to use insulin - or insulin resistance - is thought to be the main cause of type-2 diabetes, which is linked to obesity and affects more than one million Britons.

The researchers, who report their results in the journal Proceedings of the National Academy of Sciences, said that while previous studies have linked quantity of sleep with diabetes, this was the first to make the association with quality of sleep.

They added: "Since reduced amounts of deep sleep are typical of ageing and of common obesity-related sleep disorders such as obstructive sleep apnea, these results suggest that strategies to improve sleep quality, as well as quantity, may help to prevent or delay the onset of type-2 diabetes in populations at risk."

Obstructive sleep apnea is a common disorder in which breathing regularly stops or becomes very shallow during sleep.

Previous studies have linked lack of sleep to a host of health problems, including high blood pressure, obesity and memory loss.

Lack of sleep raises the risk of diabetes in the elderly

Circadian Rhythm Sleep Disorders

Circadian rhythms are regular changes in mental and physical characteristics that occur in the course of a day (circadian is Latin for "around a day"). Most circadian rhythms are controlled by the body's biological "clock." This clock, called the suprachiasmatic nucleus or SCN (see figure 2 ), is actually a pair of pinhead-sized brain structures that together contain about 20,000 neurons. The SCN rests in a part of the brain called the hypothalamus, just above the point where the optic nerves cross. Light that reaches photoreceptors in the retina (a tissue at the back of the eye) creates signals that travel along the optic nerve to the SCN. 

Signals from the SCN travel to several brain regions, including the pineal gland, which responds to light-induced signals by switching off production of the hormone melatonin. The body's level of melatonin normally increases after darkness falls, making people feel drowsy. The SCN also governs functions that are synchronized with the sleep/wake cycle, including body temperature, hormone secretion, urine production, and changes in blood pressure. 

By depriving people of light and other external time cues, scientists have learned that most people's biological clocks work on a 25-hour cycle rather than a 24-hour one. But because sunlight or other bright lights can reset the SCN, our biological cycles normally follow the 24-hour cycle of the sun, rather than our innate cycle. Circadian rhythms can be affected to some degree by almost any kind of external time cue, such as the beeping of your alarm clock, the clatter of a garbage truck, or the timing of your meals. Scientists call external time cues zeitgebers (German for "time givers"). 

When travelers pass from one time zone to another, they suffer from disrupted circadian rhythms, an uncomfortable feeling known as jet lag. For instance, if you travel from California to New York, you "lose" 3 hours according to your body's clock. You will feel tired when the alarm rings at 8 a.m. the next morning because, according to your body's clock, it is still 5 a.m. It usually takes several days for your body's cycles to adjust to the new time. 

To reduce the effects of jet lag, some doctors try to manipulate the biological clock with a technique called light therapy. They expose people to special lights, many times brighter than ordinary household light, for several hours near the time the subjects want to wake up. This helps them reset their biological clocks and adjust to a new time zone. 

Symptoms much like jet lag are common in people who work nights or who perform shift work. Because these people's work schedules are at odds with powerful sleep-regulating cues like sunlight, they often become uncontrollably drowsy during work, and they may suffer insomnia or other problems when they try to sleep. Shift workers have an increased risk of heart problems, digestive disturbances, and emotional and mental problems, all of which may be related to their sleeping problems. 

The number and severity of workplace accidents also tend to increase during the night shift. Major industrial accidents attributed partly to errors made by fatigued night-shift workers include the Exxon Valdez oil spill and the Three Mile Island and Chernobyl nuclear power plant accidents. One study also found that medical interns working on the night shift are twice as likely as others to misinterpret hospital test records, which could endanger their patients. It may be possible to reduce shift-related fatigue by using bright lights in the workplace, minimizing shift changes, and taking scheduled naps. 

Many people with total blindness experience life-long sleeping problems because their retinas are unable to detect light. These people have a kind of permanent jet lag and periodic insomnia because their circadian rhythms follow their innate cycle rather than a 24-hour one. Daily supplements of melatonin may improve night-time sleep for such patients. However, since the high doses of melatonin found in most supplements can build up in the body, long-term use of this substance may create new problems. Because the potential side effects of melatonin supplements are still largely unknown, most experts discourage melatonin use by the general public. 

Circadian Rhythm Disorder Symptoms

Symptoms commonly found in persons with a circadian rhythm disorder related to the sleep-wake cycle can include the following:

• Difficulty initiating sleep
  
• Difficulty maintaining sleep
  
• Nonrestorative sleep
  
• Daytime sleepiness
  
• Poor concentration
  
• Impaired performance, including a decrease in cognitive skills
  
• Poor psychomotor coordination
  
• Headaches
  
• Gastrointestinal distress

Circadian Rhythm Sleep Disorders