June 28, 2006  Severe hot flashes are associated with insomnia in middle-aged women, according to the results of a study from a random sample of a California population reported in the June 26 issue of the Archives of Internal Medicine.

"Because hot flashes can occur during the night, their presence has been frequently associated with insomnia in women with symptoms of menopause," write Maurice M. Ohayon, MD, DSc, PhD, from Stanford University School of Medicine in Palo Alto, Calif.

"However, many factors other than hot flashes or menopause can be responsible for insomnia, and several factors associated with insomnia in the general population are also commonly observed in perimenopausal and postmenopausal women who have hot flashes."

The investigators interviewed by telephone a random sample of 3243 subjects, aged 18 years or older, who were representative of the California population. Of the 3243 subjects, 982 were women aged 35 to 65 years; these were divided into 3 groups: premenopause (57.2%), perimenopause (22.3%), and postmenopause (20.5%). Hot flashes were counted if they occurred at least 3 days per week during the previous month, and they were classified as mild, moderate, or severe according to their effect on daily functioning. Chronic insomnia was defined as global sleep dissatisfaction, difficulty falling asleep or staying sleep, or nonrestorative sleep, for at least 6 months. Diagnoses of insomnia were classified according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition.

Hot flashes occurred in 12.5% of premenopausal women, 79.0% of perimenopausal women, and 39.3% of postmenopausal women. Chronic insomnia occurred in 36.5% of premenopausal women, 56.6% of perimenopausal women, and 50.7% of postmenopausal women (P < .001). Prevalence of symptoms of chronic insomnia increased with the severity of hot flashes. More than 80% of perimenopausal women and postmenopausal women who had severe hot flashes also had symptoms of chronic insomnia. In multivariate analyses, severe hot flashes were significantly associated with symptoms of sleep disturbance and a diagnosis of chronic insomnia. Other significant factors associated with chronic insomnia were poor health, chronic pain, and sleep apnea.

Study limitations include cross-sectional design, inability to determine causal relationship, and data based on self-reports.

"Severe hot flashes are strongly associated with chronic insomnia in midlife women," the authors write. "The presence of hot flashes should be systematically investigated in women with insomnia. Treating hot flashes could improve sleep quality and minimize the deleterious consequences of chronic insomnia."

The Arrillaga Foundation and NV Organon supported this study. The authors have disclosed no relevant financial relationships.

Arch Intern Med. 2006;166:1262-1268