Prevalence of xerostomia and its association with systemic diseases and medications in the elderly: a cross-sectional study

ABSTRACT BACKGROUND: Dry mouth syndrome or xerostomia is defined as decreased salivary flow or hypofunction of salivary glands. Its origins are multicausal and might be the result of a change in the salivary glands or a systemic imbalance. OBJECTIVE: To ascertain the prevalence of self-reported xerostomia and to identify associated factors. DESIGN AND SETTING: Cross-sectional study on the entire population of 293 elderly people over 60 years of age living in a Brazilian municipality. METHODS: Data were gathered from a questionnaire that asked about demographic data, chronic diseases and use of continuous medications, and which used the Xerostomia Inventory (XI) to evaluate dry mouth sensation. Our analysis consisted of multivariate regression and estimation of odds ratios (OR) and their respective 95% confidence intervals (CI) in binary logistic regression models. RESULTS: The prevalence of self-reported xerostomia was 19.1%. Elderly people with diabetes had higher odds of having self-reported xerostomia (OR: 3.59; 95% CI: 1.48-8.68; P < 0.001) as did those who had chronic diseases and used continuous medication (OR: 2.3; 95% CI: 1.19-4.67; P = 0.009). Elderly people who used continuous medication for the gastrointestinal tract were more likely to have xerostomia (OR: 2.14; 95% CI: 1.03-1.44; P = 0.030). CONCLUSIONS: Elderly people with diabetes and chronic diseases who were using continuous medication were more likely to have dry mouth. Use of continuous medications for the gastrointestinal tract led to a greater chance of having self-reported xerostomia.

of taste and a burning sensation in the mouth. 10 In addition, they reported that xerostomia may be a consequence of head and neck radiotherapy, depression, anxiety, stress and even malnutrition. It needs to be emphasized that some of the most common chronic conditions today are symptoms of depression and anxiety. 10 There is some evidence that certain chronic diseases might be determinants of xerostomia and/or hyposalivation. [11][12][13][14][15] One of the diseases most investigated today is diabetes mellitus (DM), a chronic disease characterized by hyperglycemia and insufficient insulin production by the pancreas. 8 The insulin that is produced has the function of regulating carbohydrate metabolism, and its absence causes glucose to remain in the bloodstream, thus characterizing a state of hyperglycemia. Hyposalivation in patients with uncontrolled diabetes might be caused by an increase in diuresis, which could affect saliva production, 16 but it might also be caused by a condition called neuropathy. [17][18][19][20] Therefore, there still seems to be much doubt concerning the cause-and-effect relationship between this pathological condition and xerostomia. 21 In addition to correlations with chronic diseases, a relationship between xerostomia and use of continuous medication has been highlighted. Wiener et al. 22 and Van der Putten et al. 23 added anticholinergic, diuretic and antipsychotic drugs to the list of associated factors. Freitas et al. 6 also included some types of analgesic and xerostomia-associated antibiotics.
Xerostomia is an important condition but is still little-known by the population and has been neglected by health professionals.
In addition, studies on this condition are scarce and unenlightening. The absence of explanations about the determining factors of this condition can be highlighted, especially in relation to the non-institutionalized elderly population. The prevalence of xerostomia in the population has been reported to range from 5.5% to 46%. 10 Gender and age-related differences have been observed, such that older individuals may have more symptoms of xerostomia. However, this could be due to the higher number of xerogenic drugs used to treat chronic diseases and might not only be related to age. 10,21 Nonetheless, these associations still seem unclear.

OBJECTIVE
Based on these scientific data, the objective of the present study was to ascertain the prevalence of self-reported xerostomia and to identify its association with chronic diseases, continuous medication use, age and gender, among elderly people in a municipality in southern Brazil.
The hypothesis for this study was that the presence of chronic systemic diseases and use of medications among the elderly people investigated would show associations with self-reported xerostomia.

This study was submitted to and approved by the Research Ethics
Committee of Faculdade Meridional (IMED), under the approval no. 2,711,544 and CAEE 90966718.0.0000.5319, on June 13, 2018, in accordance with the rules of resolution 466/12. All individuals participating in the research signed an informed consent statement in which they agreed to be part of it. Care was taken in this study to ensure confidentiality regarding identity and privacy, and also the confidentiality of the data obtained.
The present work was compiled in accordance with the recommendations of the STROBE statement (Strengthening the reporting of observational studies in epidemiology). 24

Design, sample and location of study
The present study took a quantitative approach, with a cross-sectional design. The study population consisted of the elderly population of the municipality of Vanini, which is located in the northwest of the state of Rio Grande do Sul. It has an estimated total population of 2,104 inhabitants and a total area of 69.9 km². 25 The population of Vanini over 60 years of age consisted of 300 people. 25 All of this population was eligible, but seven people were excluded from the study (see criteria, below). Thus, the study population was formed by 293 elderly people aged 60 years and over.
There were no losses in this study.

Inclusion and exclusion criteria
All the elderly population aged 60 years and over participated in this study. Only those with neurological conditions and patients with head and neck cancers undergoing radiotherapy were excluded from the study.

Data collection procedures
Data collection was performed through home visits to all houses in the municipality, made by a team composed of four students of the dentistry course, between August and September 2018.
First, a pilot test was performed on twenty elderly people in order to train the researchers to collect data and to check for possible doubts or problems relating to completion of the research instrument by the elderly subjects, thus minimizing possible bias in the research methodology. However, there were no changes to the procedures and, later on, these data from the pilot study were included in the final sample.
The data relating to the variable of self-reported xerostomia were collected by means of a validated questionnaire for xerostomia and dry mouth sensation that is used to verify cases of self-reported xerostomia. The Xerostomia Inventory (XI) includes eleven items. 26 A previous study validated this questionnaire for use among Brazilian individuals. 27 Each item in this questionnaire has five response options: never, hardly ever, occasionally, fairly often and very often. The questions are the following: "Do you have difficulties swallowing any foods?", "Do you have difficulties eating dry foods?", "Does your mouth feel dry when eating a meal?", "Does your nose feel dry?", "Does your face feel dry?", "Do you suck sweets or cough lollies to relieve dry mouth?", "Do you get up at night to drink?", "Do your eyes feel dry?", "Do your lips feel dry?", "Does your mouth feel dry?" and "Do you sip liquids to aid in swallowing food?" We added questions asking for demographic data (gender and age) and questions asking about chronic diseases and continuous medication use, consisting of the following: "Do you use continuous medications?", "Do you have diabetes, thyroid dysfunction, rheumatoid arthritis, depression and/or anxiety, HIV, hypertension and/or any other diseases?" and "Do you use medications for the stomach, cholesterol or diuretics, or do you use anticoagulants?" In addition, we also included a question on "Difficulty in using a dental prosthesis".

Outcome variable
We composed the outcome variable of this study based on studies conducted by Thomson et al. in 1999 26 and 2006, 28 which used a single question from the XI questionnaire to ascertain the prevalence of xerostomia. In the present study, we did not perform an oral clinical evaluation.
We combined the responses to the questions of the XI questionnaire into negative answers (no) = never, hardly never and occasionally; and positive answers (yes) = fairly often and very often.
Thus, people who answered positively to the XI question "My mouth feels dry" were included in the self-reported xerostomia group. 28

Covariables
The variables considered were gender (female or male), age (60 to (yes/no) and difficulty in using a dental prosthesis (yes/no).
The variable "other chronic diseases and continuous medication" (yes/no) was composed of diseases other than the most prevalent diseases mentioned previously and was considered together with use of drugs to control these diseases. This formed a reliable way of knowing whether the elderly individual was being medicated. The diseases included in this variable were fibromyalgia, Parkinson's disease, hypothyroidism, osteoporosis, cardiac arrhythmia and multiple sclerosis.

Data analysis
For the data analysis, we performed descriptive analyses and bivariate and multiple regressions. In the multiple analysis, we estimated odds ratios (OR) and their respective 95% confidence intervals, with crude variables and variables adjusted for exposure in binary logistic regression models (P-value < 0.05). The data were analyzed using the Statistical Package for the Social Sciences (SPSS) software, version 20.0 (IBM, Armonk, New York, United States). Table 1 describes the results regarding demographic variables, chronic diseases, difficulties and use of continuous medications.

RESULTS
Most of the elderly people were between 60 and 69 years old, and a majority of the population (56%) was male.
Moreover, 40.3% of them reported having other diseases, i.e. in addition to those being researched in this study. Thus, in addition to the medications used for the chronic diseases that they reported (diabetes, thyroid dysfunction, rheumatoid arthritis, depression and anxiety, HIV and hypertension), they also used cholesterol-lowering drugs (27%) and medicines for stomach and circulatory problems (17.1%). These elderly people also had other chronic diseases and used continuous medications for their control (40.3%). In the question about having difficulty in using a dental prosthesis, only 2% of the elderly people answered yes; however, 100% of them were using some type of dental prosthesis.
To perform the binary logistic regression, all variables that had an association with a P-value < 0.20 were entered into the crude

DISCUSSION
The purpose of this study was to ascertain the prevalence of selfreported xerostomia and to identify its associations with chronic diseases, continuous medication use, age and gender, among the elderly, in order to learn about these data, which had never been investigated in this location. The results showed that the prevalence of self-reported xerostomia was 19.1%, through using the XI question "Does your mouth feel dry?". It is also important to point out that 13% reported feeling "difficulties in swallowing certain foods" and 14.7% "sipped liquids to aid in swallowing food", which are important responses for indicating the presence of xerostomia.
Xerostomia is a subjective sensation of dry mouth and is assessed by asking individuals directly about their experience with this disease. According to other studies, the question " Does your mouth feel dry" reveals the prevalence of dry mouth. 26,28 Thus, salivary flow was not measured in this study. Dry mouth is an important condition that negatively impacts people's daily lives, so the results presented here should be considered with caution.
The study conducted by Thomson et al. among adults and the elderly showed that the prevalence of xerostomia was 10%, with no difference between the genders. 28 Perotto et al. 12 evaluated 117 dental patients, among whom 24.8% reported having xerostomia, which was associated with medication use. This differed from the results found by Freitas et al., 6 in which 59% of the elderly subjects reported having a feeling of dry mouth during most of the day, and this sensation was associated with the medication that they were using. The estimated global prevalence of dry mouth was found to be 22% among adult and elderly individuals in a systematic review study. 29 However, the prevalence was higher in studies conducted exclusively among elderly people, and presence of xerostomia in these studies was correlated with  In the present study, there was a statistically significant association between self-reported xerostomia and presence of the chronic disease diabetes mellitus. The chances that an individual with DM who uses continuous medication for this condition will have xerostomia or dry mouth are 3.59 times higher than among other elderly people. It should be noted that all the elderly people in the present study were using medication at the time of data collection.
In another study, presence of xerostomia among patients with decompensated DM was explained by increased diuresis or polyuria, which could affect saliva production. 13 Carda et al. 33 surveyed 33 patients with type 2 DM and found that 76.4% of them had symptoms of xerostomia. However, it has been reported that it remains undetermined whether the presence of xerostomia is higher in patients with or without diabetes. 14 In a further study, the prevalence of xerostomia among 120 elderly people diagnosed with type 2 diabetes (60 insulin-dependent individuals and 60 who did not require it) who had been undergoing treatment for at least one year using continuous medication was surveyed. Dry mouth or xerostomia was evaluated on a visual analogue scale. Among these patients, 92.5% presented hyposalivation and 49.2% had moderate to severe dry mouth or xerostomia. 15 Although the present study did not show any significant relationships with depression and anxiety, high blood pressure or thyroid dysfunction, several other studies have highlighted this association. Thomson et al. 28 found relationships between xerostomia and the use of antidepressants, iron supplements and analgesics.
The complaint of dry mouth was more frequent among adults who were using antidepressants, and also among those using other medications such as iron and narcotic painkillers. The individuals who were taking antidepressants were 22 times more likely to feel dry mouth or proper xerostomia. 28  It needs to be borne in mind, as a limitation of the present study, that its design was cross-sectional and therefore cause and effect could not be verified, considering that data were analyzed at a single moment. Another limitation that needs to be acknowledged is the fact that memory bias is possible among elderly people when they answer questions. In addition, the variable "chronic diseases and continuous use of medicines" was very broad. Nonetheless, this formed a way of including other diseases and the medicines indicated for their control. Furthermore, this study did not identify risk factors for the self-reported xerostomia analyzed here. If we had been able to evaluate long-term reports on these individuals and their salivary levels, it might have been possible to observe the incidence and factors that could interfere with this condition. Another limitation was the fact that the municipality analyzed is small and we cannot extrapolate the results to other municipalities that are not similar to this one. However, it is important to highlight that the entire population aged 60 years and over that was living in this location participated in this research.
Knowing the causes of xerostomia from self-reports given by the participants in this study will enable implementation of guidance interventions to improve these individuals' quality of life. However, the data on causality remains uncertain and more information is required in order to be able to reach conclusions regarding the determinants of xerostomia. Nonetheless, the present study is of great relevance and importance for the population surveyed, given that it provides real current data on the elderly people living in this municipality.

CONCLUSIONS
From the results we obtained in this study, it was possible to conclude that the prevalence of self-reported xerostomia among the elderly people in this municipality is moderate, which corroborates the findings in the literature.
Elderly people with diabetes and other chronic diseases using continuous medications are more likely to have dry mouth. Use of continuous medications for the gastrointestinal tract gives rise to a greater chance of having self-reported xerostomia among elderly people.