Natural Killer Cells Need A Good Night's Sleep

Researchers at the UPMC Health Systems (UPMC) Western Psychiatric Institute and Clinic in Pittsburgh studied 29 patients aged 40 to 78 who were seeking treatment for bereavement-related depression.

Each patient spent three nights in a sleep lab as part of a double-blind, placebo-controlled study of the treatment of bereavement-related depression between 1995 and 1996. None of the subjects had any infectious illnesses at the time and all were experiencing their first lifetime episode of major depression.

Analysis of their blood samples showed that those whose sleep had been disrupted had decreased levels of natural killer cells (NKCs), which take their name from the way they help destroy illness-causing cells. A decreased NKC count indicates a weakened immune system and a body more vulnerable to illness.

The study, published in the January-February issue of Psychosomatic Medicine, "provides the first direct evidence that...sleep disruptions are associated with the stress-immune relationship in humans," the researchers write. "Stress-related intrusive thoughts and avoidance behaviors were associated with greater time spent awake during the first sleep cycle which, in turn, was associated with lower numbers of circulating NKCs."

The findings prove that maintaining good sleep is important for the elderly to maintain health, according to the primary author, Martica Hall, PhD, of the University of Pittsburgh Medical College's Department of Psychiatry. She said the findings show the importance of developing interventions that reduce illnesses caused by stress-related sleep disruptions.

Although sleep disruptions associated with bereavement or other stressful life events may play an important role in illness susceptibility, Hall said, it is not yet known whether doctors can improve patients' health by improving their sleep.

"We know that it is better to treat the underlying problem, bereavement-related depression, than to simply treat the symptom, disturbed sleep, with a sleeping pill," Hall said. "The potential health benefits of treating bereavement-related depression, including its sleep disruptions, is one of the research avenues we are now following."