Prevalence of nasal polyps and its risk factors: Korean National Health and Nutrition Examination Survey 2009 –2011 Jaewoon We, M.D.,1 Woo Hyun Lee, M.D.1 Keng Lu Tan, M.D.,1 Jee Hye Wee, M.D.,1 Chae-Seo Rhee, M.D.,1 Chul Hee Lee, M.D.,1 Soyeon Ahn, Ph.D.,2 Ju Hyun Lee, M.S.,2 and Jeong-Whun Kim, M.D., Ph.D.1

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ABSTRACT

Background: Although nasal polyps (NPs) are thought to be a common otorhinolaryngologic disease, there have been few population-based epidemiologic studies on the prevalence of NPs. The aim of this study is to evaluate the prevalence of NPs and the risk factors in the general Korean population. Methods: The data were obtained from the Korea National Health and Nutrition Examination Survey (KNHANES) (2009 –2011), which was a cross-sectional survey of noninstitutionalized populations all around the country (n ⫽ 28,009). Among them, 19,152 participants (age more than or equal to 20 years) completed medical interviews, physical examinations and endoscopic examination. Analyses were performed using a complex sample design to identify the prevalence and its risk factors. Results: The weighted prevalence of NPs was 2.5%. The increased prevalence was associated with increasing age. In the multivariate analyses, male sex [adjusted odds ratio (OR) ⫽ 1.68, 95% confidence interval (CI) ⫽ 1.25–2.26], low education level (adjusted OR ⫽ 1.57, CI ⫽ 1.16 –2.13), obesity (adjusted OR ⫽ 1.49, CI ⫽ 1.19 –1.87), asthma (adjusted OR ⫽ 1.80, CI ⫽ 1.24 –2.62), and thyroid cancer (adjusted OR ⫽ 2.98, CI ⫽ 1.26 –7.09) were associated with NPs. Among those with NPs, the proportion of symptomatic NPs was 34.4% and asthma was the only significant associated risk factor. Conclusion: The prevalence of NPs in the Korean general population was not low despite advances in medical and surgical treatment and two thirds of the subjects with NPs were asymptomatic. Further investigation is needed to exhibit the causal relationship between the associated risk factors identified and NPs. (Am J Rhinol Allergy 29, e24 –e28, 2015; doi: 10.2500/ajra.2015.29.4131)

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asal polyps (NPs) are paranasal sinus mucosal outgrowths caused by chronic inflammation.1 Some recent studies proposed that NPs are the end product of chronic rhinosinusitis,2 but their actual etiology and pathogenesis are poorly understood.3 Several studies showed that NPs reduce the quality of life more than asthma, coronary artery disease, and chronic obstructive pulmonary disease.4 NPs are one of the most common diseases among ear, nose, and throat (ENT) patients. However, to our best knowledge, there have been only three population-based studies on the prevalence until now. The previous studies have shown that the prevalence ranged from 2.1% to 4.3%,5–7 but the methods used were questionable. For example, only one study used endoscopic examination to diagnose NPs, whereas the other two studies used only questionnaires to determine the diagnosis without confirmation with nasal endoscopic examination. The studies were conducted within a sample group that did not represent population of the whole country. Besides that, all of the previous studies were performed in the Western countries, and no data are available with regards to a majority of Asian population. Using the data from Korean National Health and Nutrition Examination Survey (KNHANES), our investigation was conducted to estimate the weighted prevalence of NPs diagnosed by endoscopy in the general Korean population. This study also investigated the risk factors associated with NPs through analyses of systematic medical

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Department of Otorhinolaryngology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, and 2Medical Research Collaborating Center, Seoul National University Bundang Hospital, Seongnam, South Korea J We and W H Lee contributed equally to this work The authors have no conflicts of interest to declare pertaining to this article Address correspondence to Jeong-Whun Kim, M.D., Ph.D., Associate Professor, Department of Otorhinolaryngology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, 300 Gumi-dong, Bundang-gu, Seongnam, Gyeonggi-do, 464-707, South Korea E-mail address: [email protected] Copyright © 2015, OceanSide Publications, Inc., U.S.A.

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questionnaires, endoscopic ENT examination findings, and laboratory test results.

MATERIALS AND METHODS Population The KNHANES is a cross-sectional survey conducted by the Korean Centers for Disease Control and Prevention (KCDC) assessing the health and nutrition status of South Koreans. The sample in KNHANES was extracted by a multistage clustered and stratified random sampling method to represent the civilian noninstitutionalized South Korean population. The KNHANES IV was conducted from 2007 to 2009 based on the 2005 National Census data. The KNHANES V was carried out from 2010 to 2012 based on the 2009 National Resident Demographics data. In our study, the data used were extracted from KNHANES, 2009 to 2011. A total of 34,249 individuals were sampled as subjects and 28,009 individuals participated in the survey; the response rate was 81.8%. Among the respondents, data from 19,152 adults aged 20 years and above who have completed a questionnaire on independent risk factors and underwent an endoscopic nasal examination were analyzed in this study. The average age of the 19,152 participants was 50.4 ⫾ 16.4 years (range, 20–97 years), and the ratio of male to female was 1:1.32. Written informed consents were obtained from all the participants before survey, and this research study was approved by the Institutional Review Board of the Seoul National University Bundang Hospital.

ENT Evaluation, Medical History, and Clinical Examination Each set of KNHANES was taken by a mobile unit over a period of one year across the whole country. Specific ENT history and diagnostic examinations were conducted by trained ENT residents according to standardized protocols. The quality control during the survey was governed by the Epidemiology Committee of the Korean Society of Otorhinolaryngology-Head and Neck Surgery.

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p ⬍ 0.001). This trend was also statistically significant when age was divided into groups of a decade (Fig. 1). The lowest prevalence of 1.1% was noted in the second decade twenties and the highest prevalence of 4.0% in the sixth decade of life. The prevalence of NPs according to medical conditions is shown in Table 2. A univariate analysis from this data demonstrated that hypertension, asthma, hepatitis C, gastric cancer, and thyroid cancer were significantly associated with higher prevalence of NPs.

The presence of NPs was examined using a 4-mm, 0° nasal endoscope after decongestion of the nasal cavities. Deviated nasal septum was defined when asymmetric displacement to one or both sides of the nasal cavities was observed. Benign laryngeal disease was defined as presence of lesions such as a vocal cord polyp or a laryngeal cyst, which was visualized with a 4- or 5.5-mm, 70° laryngeal endoscope. Symptomatic NPs was defined when one or more of the following symptoms were present for more than three months: nasal obstruction, anterior/posterior nasal drip, facial pain/pressure, and olfactory dysfunction. Other medical history and sociodemographic data were collected by trained interviewers of the KCDC. The level of education was categorized into two levels: those who completed from middle or elementary school were considered to have a low level education, and those who completed high school or college were considered to have high level education. Household income was categorized into low (less than or equal to 50 percentile) and high (more than 50 percentile) groups using gross household income per month. Occupation was classified into white and blue collar according to the Korean Standard Classification of Occupations. Residency was categorized into urban and rural areas according to the official address of the subjects. Obesity was defined as body mass index greater than 25 kg/m2. Alcohol consumption was assessed by the average frequency of alcoholic consumption during the month before the interview. Presence of other diseases was determined by using the question, “Have you ever had this disease?” Laboratory tests were done in NeoDin Medical Institute, Seoul, Korea, which was certified by the Korean Society for Laboratory Medicine. Based on the results of laboratory tests, dichotomous variables were created according to the normal laboratory range: anemia, hypercholesterolemia, hypertriglyceridemia, and vitamin D deficiency were defined in this manner.

Statistical Analyses

The factors associated with NPs were determined by multivariate analyses for each variable after adjusting for all of the other variables (Table 3). Old age (adjusted OR, 1.02; 95% CI, 1.01–1.03), male gender (adjusted OR, 1.68; 95% CI, 1.25–2.26), lower education level (adjusted OR, 1.57; 95% CI, 1.16–2.13), obesity (adjusted OR, 1.49; 95% CI, 1.19–1.87), asthma (adjusted OR, 1.80; 95% CI, 1.24–2.62), and thyroid cancer (adjusted OR, 2.98; 95% CI, 1.26–7.09) were significantly associated with NPs.

RESULTS

Prevalence of NPs The overall prevalence of NPs in the Korean adult population was 2.5% (95% CI ⫽ 2.2–2.9). The prevalence of NPs according to the general characteristics of participants is shown in Table 1. The univariate analyses showed that male sex, low education level, blue collar occupation, rural residency, higher body mass index, smoking, and frequent alcohol consumption were independent risk factors for NPs. A logistic regression analysis using NPs as the outcome variable and age as a continuous variable showed a significant increasing trend of the prevalence of NPs with age (OR, 1.026; CI, 1.020–1.032;

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Comparison of the Characteristics of Symptomatic NPs and Asymptomatic NPs

When the subjects were divided into symptomatic NPs and asymptomatic NPs, 34.4% were symptomatic and 65.6% were asymptomatic. Among the risk factors identified above, only asthma (adjusted OR, 2.34; 95% CI, 1.08–5.08) was significantly associated with symptomatic NPs (Table 4). There were no statistically significant differences in other variables between the two groups.

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The data were analyzed with SPSS (version 18.0, SPSS, Inc., Chicago, IL), which is a software package that assimilates sample weights and adjusts analyses for the complex sampling design of the survey. We used the KNHANES sampling weight variables which were extracted by incorporating sampling rate and response rate, along with masked variance primary sampling unit and stratum variables. This adjustment enabled a more precise estimation of the entire noninstitutionalized Korean population from the sample. The ␹2 test and univariate logistic regression analyses were used to compare the characteristics between the population with and without NPs.8 Subsequently, multiple logistic regression analyses that included variables with p ⬍ 0.20 were performed to obtain adjusted odds ratios (ORs) and their 95% confidence interval (CI). Finally, after dividing the subjects with NPs into symptomatic and asymptomatic groups, we computed their prevalence and the relevant variables with p ⬍ 0.05 using the multiple logistic regression model. By using collinearity diagnostics, collinearity of the model was assessed; variance inflation factors showed no significant collinearity between each of our variables. A p-value of less than 0.05 was considered statistically significant. Missing data were considered to be missing completely at random.

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Multivariate Analyses of Risk Factors

DISCUSSION

To the best of our knowledge, this is the first population-based study to report the weighted prevalence of NPs that was confirmed with endoscopic nasal examination. The current study found that the weighted prevalence of NPs in the Korean general population was 2.5%. A search in the literature showed that three population-based studies on the prevalence of NPs were conducted in the past. One of the studies conducted in Finland reported a prevalence of 4.3% from a sample of 3102 adults.5 The study was done using mailed questionnaire, and NPs were not confirmed with nasal examination. In another study performed in France, computer-assisted interview was carried out in a sample of 10,033 subjects,6 but nasal examination was not performed. They reported a prevalence of 2.11% in the general adult population. In our study, it was shown that 65.6% of the subjects with NPs were asymptomatic. The high prevalence of subjects who are asymptomatic suggested that accurate diagnosis of NPs could only be achieved with endoscopic nasal examination. Hence, previous studies stated above might not represent the true prevalence. The only study which could more accurately represent the true prevalence was the one done in Sweden, in which a population-based study using nasal endoscopic examination was carried out.7 From a sample of 1387, they reported a prevalence of NPs of 2.7%. However, the sample size in this study was substantially smaller than our study, and complex sampling design was not used. Therefore, we assume that our study may be meaningful for three important reasons: the diagnosis of NPs was done with nasal endoscopic examination, which is the current gold standard10; a large sample (19,152 subjects) was studied; and a complex sampling design that enables us to deduce accurate statistical results. The present study showed that several factors were associated with NPs. Increasing age was one of the risk factors. The lowest prevalence of NP was observed during the second decade and the highest during the sixth decade of life. In the past population-based studies, similar results were reported. The Swedish study observed that the prevalence NPs was less than 1% up to 40 years old, whereas the prevalence approached 5% in those 60 years of age or older.7 In the French study, the lowest prevalence was observed among those in the 18- to 24year-old group and the highest in the oldest age group (65 years or

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Table 1. Prevalence of nasal polyps according to the general characteristics of KNHANES participants (weighted for the multistage sampling design of KNHANES 2009 –2011) Characteristics

Unweighted Total Number

NPs Weighted (%) (SE)

Overall Age Sex Male Female Education Low (less than or equal to middle school) High (more than or equal to high school) Missing Household income Low (less than or equal to 50 percentile) High (more than 50 percentile) Missing Occupation White collar Blue collar Missing Residency Rural Urban Body mass index Normal (less than 25 kg/m2) Obese (more than or equal to 25 kg/m2) Missing Smoking Never Former or current Missing Alcohol drinking Less than or equal to four times per month More than or equal to two times per week Missing Influenza vaccination No Yes Missing

19,152

2.5 (0.2)

NP ⫽ nasal polyp; SE ⫽ standard error.

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older).6 Because spontaneous regression of NPs is rare and recurrence after removal is common, this could explain the consistent findings of higher prevalence of NPs among older adults. With regard to gender, we observed that NPs were more prevalent in men than women. The male preponderance of NPs has been widely reported,7,10–12 consistent

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⬍0.001 ⬍0.001 8267 10,885

3.2 (0.2) 1.9 (0.2)

7223 11,658 271

4.0 (0.3) 1.9 (0.2)

8632 10,292 228

2.8 (0.2) 2.3 (0.2)

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0.094

13,835 5079 238 4427 14,725 12,960 6093 99

T

11,022 7904 226

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Figure 1. Weighted prevalence of NPs by age groups. Increasing trend of NPs prevalence with increasing age was statistically significant (p ⬍ 0.001).

p-Value

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⬍0.001

0.015

3.3 (0.4) 2.4 (0.2)

⬍0.001

2.2 (0.2) 3.3 (0.3)

⬍0.001

2.0 (0.2) 3.2 (0.2)

⬍0.001

14,818 4038 296

2.3 (0.2) 3.4 (0.3)

11,824 7063 265

2.5 (0.2) 2.7 (0.3)

0.312

with the Swedish and Finnish population-based studies.5,7 In the French study, however, no significant difference between men and women was observed.6 We were able to confirm a relationship between asthma and NPs, as shown in the previous population-based studies.5–7 We found that 4.9% of subjects with asthma had NPs and this was significantly higher than the prevalence of NPs in the total population, which was only 2.5%. Interestingly, our study showed that obesity was associated with NPs. There is no way to confirm this finding currently. However, recently, a study by Bhattacharyya.12 reported an increased prevalence of adult obesity associated with allergic rhinitis and chronic rhinosinusitis.13 Other studies showed that obesity was associated with asthma.14 Because obesity and NPs are independently associated with higher prevalence of allergic rhinitis, chronic rhinosinusitis, and asthma, it is possible that obesity might be related to the higher prevalence of NPs. There was a significant association between NPs and education. NPs were significantly more prevalent in those with lower level of education. Although it is difficult to fully explain these associations, those with lower educational status might have less regard for diseases such as NPs, allergic rhinitis, or chronic rhinosinusitis and do not readily seek medical advices for it. Contrary to the results from previous studies, our study did not exhibit associations between NP and smoking15,16 or vitamin D deficiency.17,18 Although our study

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Table 2. Prevalence of nasal polyps according to the medical conditions of KNHANES participants (weighted for the multistage sampling design of KNHANES 2009 –2011) Characteristics ENT disease Septal deviation Benign laryngeal disease Tinnitus Cardiovascular disease Hypertension Stroke Angina Myocardial infarction Anemia Metabolic disease Diabetes mellitus Thyroid disease Hyperlipidemia Hypercholesterolemia Hypertriglyceridemia Pulmonary disease Tuberculosis Asthma Gastrointestinal disease Hepatitis B Hepatitis C Liver cirrhosis Neuromuscular disease Osteoarthritis Rheumatoid arthritis Neoplastic disease Gastric cancer Hepatic cancer Colon cancer Lung cancer Thyroid cancer Others Atopic dermatitis Depression Renal failure Vitamin D deficiency

Unweighted Total Number

NPs Weighted, % (SE)

8924 354 4050

2.4 (0.2) 2.7 (1.0) 2.8 (0.3)

4321 398 378 158 1754

3.5 (0.4) 3.3 (1.0) 2.8 (1.3) 3.3 (0.2) 2.3 (0.4)

1609 762 1944 2344 2168

3.5 (0.7) 1.7 (0.6) 3.3 (0.5) 2.6 (0.4) 2.5 (0.4)

1129 849 279 30 49

T

2849 486 129 24 66 23 155

p-Value 0.241 0.830 0.322

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O N 764 2755 61 12,377

0.002 0.405 0.806 0.700 0.726 0.073 0.217 0.071 0.974 0.902

3.5 (0.7) 4.9 (0.9)

0.104 ⬍0.001

2.5 (1.0) 14.1 (12.6) NA

0.957 0.042 0.361

3.1 (0.4) 2.1 (0.8)

0.143 0.567

5.8 (2.4) NA 3.2 (2.3) NA 7.0 (2.7)

0.041 0.476 0.742 0.532 0.008

2.5 (0.6) 2.3 (0.3) 2.4 (2.4) 2.4 (0.2)

0.943 0.514 0.963 0.203

NP ⫽ nasal polyp; SE ⫽ standard error; ENT ⫽ ear, nose, and throat; NA ⫽ not applicable.

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revealed that thyroid cancer among neoplastic diseases was associated with NPs, this association should be studied further, because the prevalence of thyroid cancer was obtained by interview of medical history. The proportion of asymptomatic subjects among those with NPs was higher than expected at 65.6%. Previous studies reported that the severity of the symptoms was associated with degree of NPs.19 We were unable to confirm this in our study, because the degree of polyposis was not documented. Our study indicated that asthma was the only risk factor associated with symptomatic NPs. It has been shown that chronic rhinosinusitis may be more common in subjects with asthma.20–22 Our study suggests that asthma may play an important role in the manifestation of nasal symptoms. Our nationwide investigation had several limitations. Firstly, as the study was done in a cross-sectional manner, only association but not causal relationship could be established. Secondly, small polyps or hidden polyps in the nasal sinuses might be missed, even with endoscopic nasal examination. In addition, no data regarding previous sinus surgeries were collected. For these reasons, the prevalence could still be underestimated. Thirdly, the data on medical history were based on selfreports and thus may be influenced by a recall bias. In conclusion, to our best knowledge, this is the first nationwide study performed among Asians showing the epidemiology of NPs. Our study

was statistically well designed and conducted by the government organization, KCDC, as well as the official organization of ENT doctors, Korean Society of Otorhinolaryngology-Head and Neck Surgery. The prevalence of NPs diagnosed by endoscopic nasal examination was 2.5% in the South Korean population, indicating that the prevalence of NPs in the Korean general population was not low despite advances in medical and surgical treatment. Our study also demonstrated that several risk factors, such as old age, male gender, lower educational level, obesity, asthma, and thyroid cancer, were associated with a higher prevalence of NPs. Based upon the results obtained in this study, further prospective studies are needed in the future to identify the causal relationship between the risk factors and NPs.

ACKNOWLEDGMENTS We thank the residents of the Department of OtorhinolaryngologyHead and Neck Surgery from 45 training hospitals in South Korea and the members of the Korea Centers for Disease Control and Prevention who participated in this survey.

REFERENCES 1.

Georgy MS, and Peters AT. Chapter 7: nasal polyps. Allergy Asthma Proc 33(suppl. 1):S22–S23, 2012.

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Table 3. Adjusted OR for the association between NPs and the risk factors Risk Factors

Adjusted OR

CI

p-Value

Age* Sex (male)* Education (less than or equal to middle school)* Household income (more than or equal to 50 percentile) Occupation (blue collar) Residency (rural) Body mass index (more than or equal to 25 kg/m2)* Smoking Alcohol drinking (more than or equal to two times per week) Hypertension Diabetes mellitus Hyperlipidemia Tuberculosis Asthma* Hepatitis C Osteoarthritis Gastric cancer Thyroid cancer*

1.02 1.68 1.57 1.11 1.10 1.13 1.49 1.09 1.21 0.87 0.93 1.07 1.17 1.80 6.02 0.89 1.48 2.98

1.01–1.03 1.25–2.26 1.16–2.13 0.88–1.41 0.85–1.43 0.82–1.55 1.19–1.87 0.83–1.42 0.94–1.56 0.65–1.17 0.62–1.41 0.76–1.51 0.76–1.80 1.24–2.62 0.61–59.88 0.62–1.26 0.61–3.59 1.26–7.09

⬍0.001 0.001 0.004 0.379 0.472 0.470 0.001 0.535 0.133 0.365 0.741 0.708 0.480 0.002 0.125 0.500 0.389 0.013

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OR ⫽ odds ratio; CI ⫽ confidence interval; NP ⫽ nasal polyp; * denotes a statistical significance with p ⬍ 0.05.

Table 4. Adjusted OR for the association between symptomatic NPs and the risk factors

T

Exposure

Adjusted OR

Age Sex (male) Education (less than or equal to middle school) Body mass index (more than or equal to 25 kg/m2) Asthma* Thyroid cancer

0.99 0.81 1.03 1.15 2.34 1.32

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CI

p-Value

0.97–1.00 0.52–1.26 0.60–1.78 0.71–1.86 1.08–5.08 0.23–7.62

0.078 0.352 0.914 0.562 0.032 0.760

OR ⫽ odds ratio; CI ⫽ confidence interval, NP ⫽ nasal polyp; * denotes a statistical significance with p ⬍ 0.05.

2. 3. 4.

5.

6. 7.

8. 9. 10.

11.

12.

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DeMarcantonio MA, and Han JK. Nasal polyps: pathogenesis and treatment implications. Otolaryngol Clin North Am 44:685–695, ix, 2011. Hsu J, and Peters AT. Pathophysiology of chronic rhinosinusitis with nasal polyp. Am J Rhinol Allergy 25:285–290, 2011. Alobid I, Benítez P, Bernal-Sprekelsen M, et al. Nasal polyposis and its impact on quality of life: comparison between the effects of medical and surgical treatments. Allergy 60:452–458, 2005. Hedman J, Kaprio J, Poussa T, and Nieminen MM. Prevalence of asthma, aspirin intolerance, nasal polyposis and chronic obstructive pulmonary disease in a population-based study. Int J Epidemiol 28:717–722, 1999. Klossek JM, Neukirch F, Pribil C, et al. Prevalence of nasal polyposis in France: a cross-sectional, case-control study. Allergy 60:233–237, 2005. Johansson L, Akerlund A, Holmberg K, et al. Prevalence of nasal polyps in adults: the Sko¨vde population-based study. Ann Otol Rhinol Laryngol 112:625–629, 2003. Corey JP. Chronic rhinosinusitis with nasal polyps (CRSwNPs) and allergic rhinitis (AR). Am J Rhinol Allergy 27:441–443, 2013. Fokkens WJ, Lund VJ, Mullol J, et al. European Position Paper on Rhinosinusitis and Nasal Polyps 2012. Rhinol Suppl 23:1–298, 2012. Collins MM, Pang YT, Loughran S, and Wilson JA. Environmental risk factors and gender in nasal polyposis. Clin Otolaryngol Allied Sci 27:314–317, 2002. Rugina M, Serrano E, Klossek JM, et al. Epidemiological and clinical aspects of nasal polyposis in France; the ORLI group experience. Rhinology 40:75–79, 2002. Larsen K, and Tos M. The estimated incidence of symptomatic nasal polyps. Acta Otolaryngol 122:179–182, 2002.

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Bhattacharyya N. Associations between obesity and inflammatory sinonasal disorders. Laryngoscope 123:1840–1844, 2013. 14. Beuther DA, and Sutherland ER. Overweight, obesity, and incident asthma: a meta-analysis of prospective epidemiologic studies. Am J Respir Crit Care Med 175:661–666, 2007. 15. Go¨rgu¨lu¨ O, Ozdemir S, Canbolat EP, et al. Analysis of the roles of smoking and allergy in nasal polyposis. Ann Otol Rhinol Laryngol 121:615–619, 2012. 16. Houser SM, and Keen KJ. The role of allergy and smoking in chronic rhinosinusitis and polyposis. Laryngoscope 118:1521–1527, 2008. 17. Schlosser RJ, Soler ZM, Schmedes GW, et al. Impact of vitamin D deficiency upon clinical presentation in nasal polyposis. Int Forum Allergy Rhinol 4:196–199, 2014. 18. Mulligan JK, Bleier BS, O’Connell B, et al. Vitamin D3 correlates inversely with systemic dendritic cell numbers and bone erosion in chronic rhinosinusitis with nasal polyps and allergic fungal rhinosinusitis. Clin Exp Immunol 164:312–320, 2011. 19. Johansson L, Bra¨merson A, Holmberg K, et al. Clinical relevance of nasal polyps in individuals recruited from a general populationbased study. Acta Otolaryngol 124:77–81, 2004. 20. Jarvis D, Newson R, Lotvall J, et al. Asthma in adults and its association with chronic rhinosinusitis: the GA2LEN survey in Europe. Allergy 67:91–98, 2012. 21. Pilan RR, Pinna FR, Bezerra TF, et al. Prevalence of chronic rhinosinusitis in Sao Paulo. Rhinology 50:129–138, 2012. 22. Chaaban MR, Walsh EM, and Woodworth BA. Epidemiology and differential diagnosis of nasal polyps. Am J Rhinol Allergy 27:473–478, 2013. e

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Prevalence of nasal polyps and its risk factors: Korean National Health and Nutrition Examination Survey 2009-2011.

Although nasal polyps (NPs) are thought to be a common otorhinolaryngologic disease, there have been few population-based epidemiologic studies on the...
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