That's the conclusion of a new study, which found that the flu shot is temporarily slowed if administered in people suffering from chronic loss of sleep. The inoculation does bounce back after several weeks. But during that window, people who got the shot while in sleep debt may be more vulnerable to infection.
The study, appearing as a research letter in tomorrow's issue of the Journal of the American Medical Association, might help explain why the flu vaccine doesn't take as well in older people, said Eve Van Cauter, a sleep expert at the University of Chicago and a co-author of the letter.
"There's very little known about the sleep needs of older adults, whether they need less or achieve less," Van Cauter said. "Certainly the data would suggest that the response to flu vaccine is less robust in the elderly."
In a previous study, John Sheridan, an immunologist at Ohio State University and a co-author of the letter, found that the combination of aging and stress greatly suppressed the immune system's response to inoculation. "Sleep deprivation is one of the most stressful things you can do to a mammal," Sheridan said.
Since the 1960s, the number of hours the average American sleeps each night has fallen from nine to seven. An estimated 70 million people in this country suffer from some form of sleeping problem, such as insomnia or apnea, according to the National Center on Sleep Disorders Research, a division of the National Institutes of Health. For 40 million of those people, the trouble is chronic. The vast majority of these nighttime woes go undiagnosed and untreated.
Previous research has shown that immune function wanes as the body amasses a sleep gap. In the new research, Van Cauter's group compared immune response to the flu vaccine in 25 young men. Eleven were allowed only four hours of sleep for six consecutive nights -- followed by a week of 12-hour spells to recover -- while the others got between 7.5 and 8.5 hours of rest after "paying back" a similar sleep debt. All the men received a flu shot on the morning after the fourth night.
Flu shots trigger a surge of blood proteins, or antibodies, that help the immune system recognize and fight the virus. But 10 days after the injections, the men who got the shot while sleep-deprived had less than half the level of antibodies (called a titer) against the pathogen than did those who were better rested when vaccinated, the researchers found.
Both groups had similar antibody titers within three to four weeks of being immunized. Still, Van Cauter said, the findings illustrate the importance of getting vaccinated while well rested. That applies to the elderly, as well as to shift workers and other people with strained sleeping habits.
Dr. Meir Kryger, a sleep researcher at the University of Manitoba, in Winnipeg, said certain body functions, like the secretion of growth hormone, are known to depend on sleep cycles and phases. So scientists have long wondered if the immune system may be vulnerable to sleep deprivation. As the latest findings suggest, "it looks like that may indeed be the case."
Although some evidence indicates that people in chronic sleep debt are more vulnerable to infections, not enough research is available on the subject, he added.
Flu vaccines have been bedeviled by delays the last two years, though last year saw only a moderate setback. The Centers for Disease Control and Prevention projects that 92 million to 97 million doses of the shot will be available this season -- or about 10 million more than in the 2001-2002 season.
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