Factors associated with night sweats
The only variable associated with pure night sweats after controlling for all other variables was panic attacks. Variables associated with night and day sweats were younger age, greater body mass index, hot flashes, chronic infection, sleep disturbances, selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants, “other” (non–SSRI, non-tricyclic) antidepressants, and xanthines.
For women, the only variable clearly associated with pure night sweats in the multivariate model was hot flashes. Panic attacks nearly reached significance (P =.026) and improved the regression model substantially (deviance reduced from 1446 to 87). Variables associated with night and day sweats were weight, sleep problems, hot flashes, antihistamines, SSRIs, and other (non–SSRI, nontricyclic) antidepressants.
For men, the only variable associated with pure night sweats after controlling for other variables was sleep problems. After exclusion of sleep problems and sedatives from the model on the assumption that they might be the result rather than the cause of night sweats, significant predictors were hot flashes (OR = 2.70; 95% confidence interval [CI], 1.35-5.40; P =.005) and regular use of multivitamins (OR = 1.87; 95% CI, 1.17-2.99; P =.009). Variables associated with night and day sweats included greater weight, hot flashes, and greater alcohol use. The ORs and CIs are shown in Table 1.
Interestingly, 32 men (5%) reported hot flashes, and those who did were more likely to report night sweats of both types. Men with hot flashes were evenly distributed across age categories. Their night sweats were more frequent, but not more severe, and they were more likely to bother others than those without hot flashes. Men with hot flashes were more likely to have told their physicians about their night sweats. After controlling for other variables, men with hot flashes were much more likely to have panic attacks (OR = 28.28; P < .001).
Patients 70 years and older made up 19.5% of our sample (N=429). The only factor associated with pure night sweats in the multivariate model was sleep disturbances (OR = 2.04; = 95% CI, 1.21-3.42; P =.007). Exclusion of sleep disturbances left no associated variables. Variables associated with night and day sweats were hot flashes (OR = 15.14; = 95% CI, 6.43-35.68; P < .001) and corticosteroids (OR = 5.45; 95% CI 1.58-18.86; P =.007).
Suspected causes
In cases where patients reported night sweats, only 19% of the patients and 18% of their physicians recorded opinions regarding causation. The suspected causes listed by patients and physicians were similar. Both groups listed menopause most frequently (48% and 44%, respectively). Other etiologies proposed were stress (12% and 8%) and medications (9% and 10%). Physicians listed diabetes as a possible cause in 11% of cases while only 4% of patients listed it. Other suspected causes included obesity, pregnancy, gastroesophageal reflux disease, sleep discomforts, and ambient temperature.
TABLE 2
Associations between independent variables and night sweats in men and women after using logistic regression modeling to control for all other variables
| Patient group | Pure night sweats | Night and day sweats | ||
|---|---|---|---|---|
| Variable | OR (95% CI) | Variable | OR (95% CI) | |
| All | Panic attacks | 4.80 (1.69-13.63) | Age* | 0.99 per yr (0.98-0.99) |
| BMI | 1.03 per unit (1.02-1.05) | |||
| Hot flashes | 7.23 (5.45-9.58) | |||
| Chronic infections | 2.05 (1.22-3.42) | |||
| Sleep problems | 1.54 (1.16-2.04) | |||
| SSRIs | 1.82 (1.22-2.70) | |||
| TCAs | 2.43 (1.25-4.74) | |||
| Other antidepressants | 2.85 (1.66-4.89) | |||
| Xanthines | 5.48 (1.60-18.81) | |||
| Men | Sleep problems | 2.54 (1.7-3.8) | Weight | per lb (1.00-1.02) |
| Hot flashes | 9.41 (4.50-19.8) | |||
| Alcohol | 3.87 (1.60-9.20) | |||
| Women | Hot flashes | 3.35 (1.13-9.95) | Weight | 1.01 per lb (1.00-1.01) |
| Panic attacks | 4.47 (1.20-16.69) | Sleep problems | 1.74 (1.30-240) | |
| Hot flashes | 6.75 (5.00-9.20) | |||
| SSRIs | 2.01 (1.30-3.10) | |||
| Other antidepressants | 2.85 (1.70-5.90) | |||
| Antihistamines | 1.88 (1.20-2.90) | |||
| *Younger age was associated with a greater likelihood of night and day sweats. Otherwise, presence of or increasing amount of each variable was associated with a greater likelihood of night sweats. | ||||
| OR denotes odds ratio; CI, confidence interval; BMI, body mass index; SSRIs, selective serotonin reuptake inhibitors; TCAs, tricyclic antidepressants. | ||||
Discussion
As far as we know, this is the first systematic study of night sweats in a primary care population. It is exploratory in nature, and, because of its cross-sectional design, no firm conclusions can be drawn about causation.
Both pure night sweats and night and day sweats are extremely common, with a peak prevalence in men and women 41 to 55 years of age. In contrast to pure night sweats, night and day sweats are experienced infrequently by patients 70 years and older. The factors associated with pure night sweats are somewhat different than those associated with night and day sweats, suggesting different, though probably overlapping, sets of causes. The different associations seen for men and women, and for older and younger patients, are also noteworthy. Patients often fail to report night sweats to their primary care physician, even when frequent and severe, associated with sleep disturbances, or bothersome to others.
Because of the sampling method (ie, consecutive patients rather than a random sample of active patients), the prevalence estimates reflect the frequency at which physicians can expect to encounter patients with this symptom, rather than the prevalence of night sweats among active patients. Since patients with more symptoms probably see physicians more often, we assume we have overestimated the true prevalence of night sweats in the larger population. Participating physicians were also not selected randomly. It is impossible to know how this may have affected our results.