We were surprised that so few of our independent variables were associated with pure night sweats: only panic attacks (all patients), sleep disorders (men and older patients), and hot flashes (women). Factors not associated with pure night sweats included obesity; diabetes, insulin, or oral hypoglycemic agents; acute or chronic infections; gastroesophageal reflux disease; or thyroid medications. Pure night sweats were also not specifically associated with estrogen and progesterone, although they were associated with hot flashes. There was also no association of pure night sweats and alcohol consumption.
The fact that physicians and their patients could only speculate on a cause for night sweats in 1 out of 5 cases suggests a lack of familiarity with the multitude of suspected causes, a failure to detect certain common causes (eg, sleep disorders and panic attacks), or, most likely, that many common causes of night sweats have yet to be elucidated. If the last is correct, it may be an example of the bias in the primary and secondary clinical literature that occurs when clinical research is carried out primarily in the subspecialty clinics of academic medical centers.4-7 Our findings speak to the need for greater support for primary care practice-based research.8,9
In retrospect, the omission of the variable “panic attacks” from the Oklahoma cards was a mistake, since this variable was correlated with pure night sweats in women. It may have been more strongly associated with pure night sweats in men as well, if the number of respondents to this question had been larger. Also, some men complained of hot flashes, and when they did, they were more likely to have night sweats and panic attacks, suggesting that both hot flashes and night sweats in men should prompt physicians to ask additional questions about panic disorder. Although race was also omitted from the Oklahoma cards, this variable did not seem to be associated with differences in night sweats prevalence or association among those for whom this information was available.
The definition and description of night sweats used in this study were arbitrary and may have influenced the prevalence rates obtained. We attempted to exclude environmental temperature as a cause. Although the definitions provided clearly stated “within the last month,” the data collection cards did not specify a time interval. This may have resulted in some variation in interpretation.
The decisions that were made regarding logistic modeling strategies were conservative and may have excluded some important variables. However, with so many variables and no basis on which to judge a priori, we felt that a conservative approach was best. The decision to include in the models variables (eg, sleep problems and sedatives that might be considered consequences) rather than causes of night sweats, was also arbitrary and may have affected the results. An alternative explanation of the associations found between night sweats and sleep problems is that those who are unable to sleep for other reasons are more likely to notice excessive sweating than those who are asleep.
Future studies should more carefully examine factors found in this study to be associated with night sweats, such as panic attacks and sleep disorders, and other potential etiologic factors not considered, such as tobacco abuse, allergic diseases, migraines, congestive heart failure, and chronic lung disease. Given the high prevalence, future studies examining etiology should include appropriate control groups. Case-control and prospective studies should evaluate the natural history of both night sweats patterns and their association with quality and length of life. The potential value of night sweats as a clue to the early diagnosis of important under-recognized pathologies, such as sleep disorders and panic attacks, should be investigated. Finally, randomized trials of treatments to reduce the frequency, severity, and impact of night sweats should be undertaken once the potential causes have been better elucidated.
Acknowledgments
This research was made possible by a grant from the American Academy of Family Physicians Foundation. We would like to acknowledge the assistance of Lavonne Glover in preparing the manuscript and to the following practicing family physicians and their staff who made time in their busy schedules to collect the data: Nathan Boren, Jo Ann Carpenter, Stephen Cobb, Ed Farrow, Cary Fisher, Helen Franklin, Kurt Frantz, David Hadley, Terrill Hulson, Joe Jamison, Dee Legako, Migy Mathew, Tomas Owens, John Pittman, Mike Pontious, Paul Preslar, R. Scott Stewart, David Strickland, Clinton Strong, Terry Truong, Keith Underhill, Kyle Waugh, Dan Woiwode, Mike Woods, Rick Edwards, Bob C. Jones, Leah R. Mabry, Tom Mueller, Mike Ragsdale, Hugh Wilson, Frank D. Wright, and Samuel T. Coleridge.