Unraveling sleep disorders of the aged.

Unraveling sleep disorders of the aged

An overactive sympathetic nervous system may prevent elderly people from getting a good night's sleep, according to Seattle researchers who suggest that the sympathetic nervous system, which is responsible for arousal, increases its activity with age. The scientists hope their work will eventually spawn new treatments for an age-old problem.

Michael V. Vitiello of the University of Washignton and his colleagues studied nine healthy men aged 22 to 25 who were good sleepers. Participants checked into a sleep laboratory for three 96-hour periods, receiving one of three exeperimental diets designed to manipulate the sympathetic nervous system. Diets consisted of hospital food altered to contain 500 milligrams of sodium per day (low), 2,000 mg of sodium per day (moderate) or 5,000 mg of sodium per day (high).

The researchers used the low-sodium diet to boost activity of the sympathetic nervous system, hoping to mimic sleep disturbances seen in the elderly. A low-sodium diet triggers water loss from the body, which results in a blood pressure decline, Vitiello explains. The sympathetic nervous system senses the body's water loss and releases norepinephrine, a neurotransmitter that constricts blood vessels, thereby maintaining blood pressure. Vitiello and his collegues speculated that the increased activity would keep their young subjects tossing and turning at night--a time when the sympathetic nervous system typically slows down.

In studying the sleep patterns of the three groups, the team found that men on the low-sodium diet awoke an average of nine times during the night, while men in the moderate-and high-sodium groups awoke five times. The low-sodium group spent about 53 minutes awake per night, whereas men in the other groups were awake for about 22 minutes. Moderate- or high-sodium subjects spent about 95 percent of their time in bed asleep; low-sodium subjects had a sleep efficiency of only 88 percent.

"Perhaps it is the sympathetic nervous system that is contributing to the disturbed sleep of the elderly," Vitiello reported last week at the annual meeting of the Association of Professional Sleep Societies in Washington, D.C. "But the conclusions aren't that one should go out and eat a lot of salt in order to sleep better. That would be the last thing I would want people to do."

Vitiello points out that the sodium manipulation in his study was for experimental purposes only. There is no evidence showing that a high-salt diet would help elderly people sleep better over the long run, and very salty diets can contribute to other problems such as high blood pressure, he notes.

Vitiello's group has carried the research one step farther by giving elderly men diets with varying sodium contents. The researchers have not yet analyzed the data, but they postulate that elderly men on a low-sodium diet will experience a detrioration of their sleep. Exercise may be one possible remedy, says Vitiello, noting that physical activity is thought to subdue the sympathetic nervous system.