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(Chest. 2006;129:933-941.)
© 2006 American College of Chest Physicians

Risk Factors Associated With Snoring in Women With Special Emphasis on Body Mass Index*

A Population-Based Study

Malin Svensson, MD; Eva Lindberg, MD, PhD; Tord Naessen, MD, PhD and Christer Janson, MD, PhD

* From the Department of Surgical Sciences (Dr. Svensson), Section of Otorhinolaryngology and Head and Neck Surgery, and the Department of Medical Sciences (Drs. Lindberg and Janson), Section of Respiratory Medicine and Allergology, and the Department of Women’s and Children’s Health (Dr. Naessen), Section for Obstetrics and Gynecology, Uppsala University, Sweden.

Correspondence to: Malin Svensson, MD, Otorhinolaryngology and Head and Neck Surgery, Akademiska sjukhuset, SE-751 85 Uppsala, Sweden; e-mail: malin.l.svensson{at}akademiska.se

Abstract

Study objectives: Habitual snoring may be regarded as an indicator of sleep-disordered breathing, and the health consequences of sleep-disordered breathing are well-known. The aim of this study was to analyze the risk factors associated with habitual snoring in a large sample of women, with special emphasis on the determinants of snoring in women with different body mass index (BMI) levels.

Design and setting: A cross-sectional, epidemiologic, population-based study was performed by using a postal questionnaire that was sent to a randomly selected sample of 6,817 women ≥ 20 years of age in Uppsala, Sweden.

Results: The total prevalence of self-reported habitual snoring was 7.6%. There was a clear age dependence, with the highest prevalence of habitual snoring (14%) occurring between the ages of 50 and 59 years. Self-reported habitual snoring was related to BMI, neck circumference, and smoking ≥ 10 cigarettes a day, after adjusting for possible confounders. When analyzing the influence of different risk factors in separate BMI groups, the results varied among the groups. The influence of alcohol dependence on snoring frequency was only significant in women with a BMI of < 20 kg/m2, while physical inactivity was only associated with habitual snoring in women with a BMI of ≥ 30 kg/m2.

Conclusions: The prevalence of self-reported habitual snoring in women was strongly dependent on age and BMI. The importance of other risk factors differed depending on BMI, with alcohol dependence being associated with self-reported snoring in lean women, whereas physical inactivity was a risk factor for self-reported snoring in women with a high BMI.

Key Words: body mass index • population based • risk factors • snoring

Snoring may be regarded as an indicator of sleep-disordered breathing, as the pathophysiology behind the snoring (ie, the vibration of tissues in the oropharynx-pharynx) and obstructive events in the airway are often the same. Habitual snoring has been said to be the best predictor of sleep apnea in both men and women,1 and it is indicated as a risk factor for developing obstructive sleep apnea.2 The health consequences of sleep-disordered breathing have been described in a very large number of articles relating to both cross-sectional studies and prospective studies.3456 Furthermore, snoring has implications for daytime performance and well-being.78910 Snoring alone has also been indicated as an independent risk factor for developing hypertension,511 stroke, and myocardial infarction.12

Risk factors associated with snoring have been analyzed in previous epidemiologic studies. The association between snoring and obesity is fairly well-established.13 Since previous data relating to the impact of other risk factors associated with snoring such as smoking, alcohol consumption, and so forth, are not conclusive11131415161718 we hypothesized that the discrepancy is not only methodological and that the risk factors may covary with the presence of overweight and obesity. Studies in which the risk factors are analyzed separately for different body mass index (BMI) groups have not previously been published. The aim of this study was to analyze the risk factors associated with snoring in a large population-based sample of women, with special emphasis on factors associated with snoring in women with different BMI levels.

Materials and Methods

Population
In this study, "Sleep and Health in Women," 10,000 women ≥ 20 years of age were randomly selected from the population registry of the Municipality of Uppsala, Sweden. They were all sent a postal questionnaire in April 2000. All of the women were sent a postcard after 1 week as a reminder, and the nonresponders received two more questionnaires at the very most. The informed consent of all participants was obtained, and the study was approved by the Ethics Committee at the Medical Faculty at Uppsala University.

Questionnaire
The questionnaire comprised 109 questions, including questions on snoring and potential risk factors for snoring. The subjects were asked about their weight and height, and their BMI (expressed in kilograms per square meter) was calculated. In multivariate analyses, BMI was categorized into the following four groups: underweight (BMI < 20 kg/m2); normal weight (20 to <25 kg/m2); overweight (25 to <30 kg/m2); and obese (≥ 30 kg/m2). Responders were also asked to measure their neck and waist circumferences according to specific instructions using a tape measure enclosed with the questionnaire. Four hundred of the women were reexamined, and height, weight, and neck and waist circumferences were measured. There was a fairly good correlation between the BMI calculated from self-reported data and that calculated with measured data (r = 0.86; p < 0.0001). There was also a reasonably close correlation between self-measured and true neck and waist circumferences (neck circumference, r = 0.86 and p < 0.0001; waist circumference, r = 0.80 and p < 0.0001).

Snoring habits were evaluated according to a 5-point scale. Habitual snoring was said to occur in patients reporting loud and disturbing snoring "often" or "very often," whereas subjects reporting loud and disturbing snoring "never," "seldom," or "sometimes" were characterized as being nonhabitual snorers.17 The subjects were also asked whether or not they usually shared a bedroom with another person.

Smoking habits were assessed using six questions; the subjects were asked whether they had ever smoked regularly for at least 6 months, and whether they were current smokers and, if so, how many cigarettes a day they smoked. Those subjects who had smoked at some time were asked about the ages at which they started and at which they quit. The subjects were categorized into the following groups: nonsmoker (ie, never smoked); previous smoker (quit smoking at least 6 months prior to answering the questionnaire); current smoker of < 10 cigarettes a day; and current smoker of ≥ 10 cigarettes a day.

Alcohol dependence was classified according to the cut down, annoyed by criticism, guilty about drinking, eye-opener drinks (CAGE) alcohol screening questionnaire.1920 The confirmation of two or more of the four questions classified the subject as alcohol-dependent. Moreover, the subjects were asked about current, regular medication.

Physical activity was classified into the following two categories: low physical activity; and normal-to-high physical activity. The women in the low-activity group confirmed spending most of their leisure time on sedentary activities, while the other women spent at least 4 h a week on activities such as gardening, cycling, or more intensive physical activities. The categorization was adopted from a large population-based, prospective study21 of the correlation of physical activity to mortality in women.

The questionnaire contained 15 questions relating to menopausal and hormonal status. The subjects were asked whether they had passed into menopause, and, if they had not, the date of their last menstrual period and whether their menstrual periods were regular. Information on current contraceptive methods, pregnancy, or breast-feeding was obtained. The subjects were asked whether they were receiving current hormone replacement therapy (HRT) with estrogen. On the basis of this information, we adopted a probabilistic approach with weighting factors to assign the women to different groups.22 Women who stated that they had regular menstrual periods, were not receiving HRT, and had not passed into menopause were regarded as being premenopausal. Women who answered that they had passed into menopause, had had their last menstrual period at least 12 months ago, and were not receiving HRT were assigned to the postmenopausal group. With these strict criteria for menopausal status, 40% of the population could be classified. Of the women who were ≤ 46 years of age, at least 94% were classified as being premenopausal, while at least 93% of the women ≥ 53 years of age were considered to be postmenopausal. We therefore thought it reasonable to divide the subjects into the following groups when performing our statistical analyses: women ≤ 46 years of age were categorized as premenopausal; women ≥ 53 years of age were assigned to the postmenopausal group; and women 47 to 52 years of age comprised a group with uncertain menopausal status.

Statistical Analysis
Statistical analyses were performed using a statistical software package (Statview, version 5.0; SAS Institute; Cary, NC). The results are presented as the mean ± SD. Associations are expressed as odds ratios (ORs) with 95% confidence intervals (CIs). In all of the statistical tests, the null hypothesis was rejected at the 5% level (p ≤ 0.05). Multiple logistic regression analysis was used to adjust for possible confounders. The correlation between neck and waist circumference was analyzed using simple linear regression. Due to the strong correlation between neck and waist circumference (r = 0.62; p < 0.0001), only neck circumference was included in most of the multivariate analyses. In order to be able to analyze the influence of waist circumference on the prevalence of self-reported snoring at different BMI levels, the multivariate analyses were repeated with waist circumference instead of neck circumference, whereas all of the other confounders were identical.

Results

Of the 10,000 questionnaires, 158 were returned unopened due to an incorrect address. The response rate was 71.6%, leaving a total of 7,051 questionnaires to be analyzed. The final study population comprised the 6,817 women who answered the question about snoring (96.7%). When analyzing the response rate for each 10-year stratum, there were no significant differences within the 20 to 69 year-old age group, while the response rate at higher ages was lower. For each age group < 70 years of age, 9.2 to 10.0% of the total female population in the actual geographic area participated in the present study. In the groups of subjects 70 to 79 years of age and ≥ 80 years of age, the corresponding participation rates were 7.8% and 4.4%, respectively.

Risk Factors Associated With Snoring
In the whole group, the total prevalence of self-reported habitual snoring was 7.6%. The snorers were significantly older, had a higher mean BMI, and had higher neck and waist circumferences compared with the nonsnorers. Habitually snoring women were more often smokers and were less physically active compared with the nonsnorers. The difference in the prevalence of alcohol dependence was not significant between the groups, but more women in the snoring group stated that they used benzodiazepine medications regularly (Table 1 ).


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  		Table 1. Characterization of a Random Sample of Women ≥ 20 Years of Age

 
Age
The mean age of the respondents was 44.8 ± 17.5 years. In the following analyses, age was categorized into groups with 10-year increments. The prevalence of self-reported habitual snoring was highly age-dependent. The prevalence was 2.5% in the group 20 to 29 years of age, with a prevalence increasing with age to 14.0% in the group 50 to 59 years of age, followed by a decline at higher ages (Fig 1 ).


Figure 1
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  		Figure 1. Prevalence of self-reported habitual snoring by age in a random sample of women (n = 6,817).

 
Anthropometric Variables
Both neck and waist circumferences were correlated to the prevalence of self-reported habitual snoring. We found a strong correlation between the prevalence of self-reported habitual snoring and BMI (Table 1, Figs 234 ).


Figure 2
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  		Figure 2. Prevalence of self-reported habitual snoring by BMI (n = 6,765).

 

Figure 3
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  		Figure 3. Prevalence of self-reported habitual snoring by neck circumference.

 

Figure 4
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  		Figure 4. Prevalence of self-reported habitual snoring by waist circumference.

 
Multivariate Analyses
Since both age and anthropometric variables had a strong influence on the risk of self-reported habitual snoring, multivariate analyses were performed to study other risk factors. To analyze whether risk factors for self-reported habitual snoring differ with BMI, multiple logistic regressions were performed for each BMI group separately (Table 2 ). The influence of neck circumference and physical activity on the risk of being a habitual snorer increased with increasing BMI. Neck circumference was only significantly associated with self-reported habitual snoring in women with a BMI of ≥ 25 kg/m2, while physical inactivity was associated with self-reported habitual snoring in women with a BMI of ≥ 30 kg/m2. In contrast, the influence of alcohol dependence on the prevalence of self-reported habitual snoring decreased with increasing BMI and was significant only in women who were regarded as being underweight (ie, BMI < 20 kg/m2). Among the women of normal weight, there was a dose-response relationship between smoking and self-reported habitual snoring, while no significant association between smoking and snoring was found in any of the other BMI groups.


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  		Table 2. Risk Factors Associated With Self-Reported Habitual Snoring in a Random Sample of Women in Different BMI Groups*

 
We analyzed the subgroups of subjects who were < 55 years and ≥ 55 years of age separately, due to the fact that the prevalence of habitual snoring increased until the age of 55 years, only to decline at older ages. In a logistic regression model adjusting for potential confounders, we found that, in both younger and older age groups, an increase in neck circumference, obesity, and smoking of ≥ 10 cigarettes a day were independently associated with self-reported habitual snoring. In the younger age group, overweight (ie, BMI 25 to 30 kg/m2) also correlated to self-reported habitual snoring (Table 3 ).


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  		Table 3. Risk Factors Associated With Self-Reported Habitual Snoring in a Random Sample of Women by Age*

 
Menopausal Status and HRT
When applying the age-based menopausal classification used above in the logistic regression analysis, no significant correlation was found between menopausal status and the prevalence of self-reported habitual snoring. Adding the use of estrogens did not affect the results, even in the postmenopausal group. To exclude the risk of data misinterpretation due to a misclassification of the menopausal groups, we performed the same logistic regression analysis applying the strict criteria for menopausal status mentioned above for premenopausal and postmenopausal subjects, but not even in these calculations did we find any significant correlation between menopausal status and the prevalence of self-reported habitual snoring.

Discussion

Our main findings were that the prevalence of self-reported habitual snoring in a randomly selected sample of women was strongly age-dependent and peaked within the age range of 50 to 59 years. The prevalence also increases with increasing BMI. The relative independent ORs for other risk factors such as smoking, alcohol use, and physical activity differ among the subject categories of BMI.

In this study, the peak prevalence rate of self-reported habitual snoring was found to occur between 50 and 59 years of age. In a population-based, prospective survey of men17 using the identical definition of habitual snoring, we found a similar age dependence in the prevalence of self-reported snoring. In a previous epidemiologic survey11 of middle-aged women, the prevalence of habitual snoring increased until the age range of 55 to 59 years, but older women were not investigated, whereas, in another population-based study,23 a peak prevalence rate of habitual snoring was reported at 60 to 64 years of age in women. In a prospective study,24 an age of ≥ 65 years was associated with a remission in reported snoring.

The finding that the prevalence of self-reported habitual snoring increases with increasing BMI is in accordance with other studies.11131425 The importance of BMI as a risk factor that is associated with habitual snoring in our sample varied according to age; in the younger women, both overweight and obese women (ie, BMI ≥ 25 kg/m2) ran an increased risk of being habitual snorers, while among the older women only obesity (BMI ≥ 30 kg/m2) was linked to self-reported habitual snoring. The correlation between obesity and snoring was stronger in subjects in the younger age group compared with the older one.

Several studies have reported a positive correlation between neck circumference and both snoring26 and sleep-disordered breathing.27282930 A gender-specific correlation between the anthropometric variables has been previously demonstrated; in 250 patients undergoing polysomnography, neck circumference correlated more closely with AHI than waist circumference in women, while the opposite was true among men.31 However, the associations among different BMI groups have not previously been analyzed. Our data indicate that, at least in women, the association between waist circumference and the prevalence of self-reported habitual snoring is of a similar magnitude, regardless of BMI, while neck circumference becomes more important the more overweight the subject is. It is possible to speculate that these differences might be due to that fact that increasing neck circumference is a better surrogate measure for increasing central obesity than waist circumference in women.

We found a dose-response relationship between smoking and self-reported habitual snoring only in women of normal weight. A correlation between smoking and an increased risk of snoring has been demonstrated in previous studies,1113 and a dose-response relationship1415 has also been detected. The effect of smoking on the patency of the upper airway might be twofold. An irritant effect of the smoke on the mucosa in the nose and pharynx may produce edema, resulting in the narrowing of the upper airway.14 Moreover, a positive effect of nicotine on the upper airway musculature in animals has been shown,32 as well as a decrease in the number of apneas occurring 2 h after the administration of nicotine to eight patients with sleep apnea syndrome.33 This may suggest that the withdrawal of nicotine during the night could increase the resistance in the upper airway.

In our material, alcohol dependence, as defined by the CAGE alcohol-screening questionnaire, was only independently correlated to self-reported habitual snoring in the women who were regarded as being underweight. In previous epidemiologic studies in which the relationship between alcohol and snoring or sleep-disordered breathing has been analyzed, a positive relationship has been found by some1416 but not by others.131718 Experimental studies have shown that alcohol ingestion increases the duration and frequency of occlusive episodes in the upper airway.3435 The authors suggested that this was due to induced oropharyngeal muscle hypotonia and the depression of arousal mechanisms. To our knowledge, no analyzes relating to alcohol and snoring have previously been conducted separately in different BMI categories, whereas a stronger effect by smoking on the prevalence of snoring was found in nonobese subjects compared with obese subjects in one study.14 It is possible to speculate that the mechanisms described above are more important in women who are underweight or of normal weight, who are less likely to have anatomic abnormalities in the upper airway in the form of fat deposits as an explanation for their snoring, compared with overweight women.

The use of sedatives is implicated as a risk factor for habitual snoring.14 Our results revealed a significant difference in the use of benzodiazepines between nonsnorers and snorers. However, after adjustments had been made for other risk factors, the use of benzodiazepines did not appear to significantly influence the prevalence of self-reported habitual snoring. Since the number of respondents using benzodiazepines was relatively low, it is difficult to draw any conclusions from this material.

A low level of physical activity was associated with a higher risk of self-reported habitual snoring in obese women in our population. An association between a low level of physical activity and snoring in men has been indicated in one study,36 in which men who reported a low level of physical activity had a higher prevalence of snoring, even when adjusting for age and obesity. An association between nasal obstruction and sleep-disordered breathing has been reported,37 and physical activity, in turn, has been shown to reduce nasal congestion by sympathetic activity.3839 The clinical implication of this connection is, however, still unexplored. Whether physical inactivity truly is a risk factor that is associated with snoring or is instead a consequence of daytime sleepiness and fatigue remains unclear.

In the present study, no correlations were found between self-reported habitual snoring and menopausal or HRT status. A significant increase in obstructive sleep apnea after menopause has been found in previous population-based female population samples investigated by polysomnography.4041 One of these studies41 also reported an increase in snoring in postmenopausal women who were not receiving HRT but not in those who were receiving HRT, whereas the prevalence of symptomatic OSAS was unrelated to menopausal status. One possible explanation for the diverging results relating to changes in reported snoring and the measured number of apneas at menopause may be that snoring is a less useful marker of sleep apnea in elderly women than in younger women. The strength of this study is that we included a large cohort of women who were randomly selected from the general population with a fairly even representation from each age group.

There are also some important limitations to the study. As in all questionnaire-based studies, there is always a risk of respondents being healthier than the population in total. The study was based on self-reported data, and the validity of self-reported snoring data has been discussed.42 When analyzing the validity of the question used to evaluate snoring, no significant differences were found between subjects in younger and older age groups when it came to the validity of self-reported snoring compared with snoring measured during 1 night.43 This investigation was, however, performed on men, and it is possible that the discrepancy between self-reported and actual snoring in women may differ from that in men. In our questionnaire, the answer to the question about snoring was formulated without the option "do not know." It is possible to speculate that there might be a tendency toward the answer "never" or "seldom" among those who are oblivious of whether they snore. Furthermore, since 2,240 women (32.9%) answered that they did not share a bedroom with another person, there is a risk of underestimating the prevalence of self-reported habitual snoring. However, there was no significant difference in the prevalence of self-reported habitual snoring (7.5% vs 7.8%, respectively; p = 0.85) or mean BMI (23.2 vs 24.2 kg/m2, respectively; p = 0.22) between those subjects who shared a bedroom and those who did not.

The number of subjects who reported habitual snoring in the subgroups of subjects with BMIs of < 20 and 20 to <25 kg/m2 was relatively small. Conclusions relating to differences between BMI subgroups must therefore be drawn with caution. However, there was a clear tendency toward an increase in low physical activity and a reduction in the influence of alcohol dependence with increasing BMI (Table 2). This is a strong indicator that the relative importance of different risk factors for self-reported habitual snoring changes across categories of BMI. We have investigated a surrogate measure (self-reported snoring) for sleep-disordered breathing (sleep apnea); the question of whether risk factors for sleep apnea differ with age and BMI in a similar manner remains to be investigated. We conclude that the importance of risk factors, other than age and BMI, associated with self-reported habitual snoring in women may change across categories of BMI.

Footnotes

Abbreviations: BMI = body mass index; CAGE = cut down, annoyed by criticism, guilty of drinking, eye opener drinks; CI = confidence interval; HRT = hormone replacement therapy; OR = odds ratio

The work was supported by grants from the Swedish Heart and Lung Foundation.

Received for publication July 30, 2005. Accepted for publication January 24, 2006.

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