Introduction
n recent years, the world’s population has shifted to aging. The people aged 60 and over are growing faster than any age group. In 2019, the number of people aged 60 and over was 1 billion. This number will increase to 1.4 billion by 2030 and 2.1 billion by 2050. This trend of change will accelerate in the coming decades, especially in developing countries [1]. The population aged 60 and over in Iran will increase to 25% in 2050 [2]. With the increase in the elderly population, the needs and problems of this population in the field of personal hygiene, especially oral health, increase. Therefore, it will affect the use of health care services and the costs associated with it [3, 4]. Oral health plays an essential role in determining food intake patterns, meeting nutritional needs, and consequently keeping the health of the elderly and their quality of life. There is ample evidence that untreated oral disorders not only have a negative impact on a person’s general health but also increase the risk of diabetes and cardiovascular diseases. Poor oral hygiene can increase the risk of such diseases by about 20% [5, 6]. Oral problems have a negative impact on nutrition, self-esteem, social relationships, physical and mental health, and the overall quality of life of people, including the elderly [7, 8].
Oral health refers to the health of the oral cavity and related tissues that prepare a person for good eating, talking, and social relationships [9]. Reasons such as insufficient motivation in dental care, forgetfulness, inability to perform individual and daily tasks, financial poverty, and side effects due to the combined use of various drugs affecting the natural physiology of the glands and cells of the oral system, and the amount of saliva secretion can cause poor oral health in the elderly [10]. Meanwhile, health literacy is one of the factors affecting the health and oral health of individuals and is effective in creating higher costs in the health system [11]. Health literacy refers to cognitive and social skills to access, understand, and better use health information and services to promote and maintain health [12]. A review study by Mir Mohammadkhani reports that the level of health literacy of the elderly in Iran is low, and aging is the cause of cognitive problems in the elderly, which can be an obstacle to obtaining information and increasing health literacy of the elderly [13]. Another factor related to oral health is nutritional status. Healthy eating is an essential part of the health of the elderly that has a unique role in promoting their health [14]. In the study of Payahoo et al., more than 50% of the elderly in Tabriz City, Iran, had an unfavorable nutritional status [15]. The result of a study that its research population consisted of adults in Tehran has shown that two-thirds of the participants consumed sweet drinks and snacks between meals, which can harm the oral health of individuals [16].
On the other hand, in the research studies, different results have been obtained regarding increasing the age of people with increasing or decreasing oral health literacy [17 18]. In contrast, in the Nezafati’s study in Rasht City, Iran, more than 50% of the elderly have sufficient health literacy [19]. According to what was discussed, the present study was conducted to determine oral health status and the relationship between health literacy and nutritional status in the elderly referring to health centers in Tabriz. The results of this study can be used in educational interventions to promote the health of the elderly and the necessary training for elderly caregivers.
Materials and Methods
The present cross-sectional analytical study was performed on the elderly in Tabriz from June to September 2020. According to the study of Ahmadi et al. and the report of adequate oral health status in the elderly at 37.44% [20], taking into account the 95% confidence level and measurement error of 0.05 (d=0.05), the required number of samples was calculated to be 242. To compensate for sample loss and incompleteness of the questionnaires, 25% was added to the final sample volume. Therefore, the final sample size was 300. The study participants were collected by a simple random method using household numbers registered in health centers until the sample size was completed. The inclusion criteria included being 60 years and older, being able to speak, lacking memory impairment, having a health record in urban health centers, willingness, and informed consent to participate in the study. The exclusion criteria included incomplete completion of questionnaires.
Montazeri et al. developed the Health Literacy for Iranian Adults Questionnaire (HELIA). It was used to assess health literacy [21]. This questionnaire has 33 items (Likert 5-point criterion) that measures people’s health literacy in 5 dimensions: reading, access, comprehension, behavior, evaluation, and decision-making. Criteria for measuring health literacy based on the Likert scale were adjusted so that the subjects expressed their opinions in 5 options (always= 4, often= 3, sometimes= 2, rarely= 1, and never= 0). The raw score of each person in each dimension is obtained from the sum of points, then converted to the range of zero to 100 and into four levels of inadequate (0-50), borderline (50-66), sufficient (66-84), and excellent (84 -100) [16]. In this study, two levels of sufficient and excellent were considered together as sufficient levels (66-100). In the present study, the Cronbach α of the questionnaire was reported as 0.79 based on a pilot study of 30 older adults selected according to the study criteria. These people did not enter the main study.
The Geriatric Oral Health Assessment Index (GOHAI) was used to assess oral health status. Atchison et al. [22] presented this questionnaire in 1990, and Rezaei reviewed its validity and reliability in Iran [23]. The GOHAI questionnaire consists of 12 questions rated on a 5-point Likert-type scale: never, rarely, sometimes, often, and always. The total score of each person is obtained from the sum of the digits related to 12 items, and the digit is between 12 and 60. In this way, a score of 5 and always a score of 1 is given, and the higher the total number of questionnaires, the better the oral health in a person’s life. In the present study, the Cronbach α of the questionnaire was reported 0.74.
The SCREEN II (seniors in the community: risk evaluation for eating and nutrition) questionnaire was used to assess the nutritional status of the elderly. This questionnaire was validated by Keller et al. in 2005 and was designed to assess weight changes and the ability to prepare food items [24]. The questionnaire consists of 14 questions that include eating habits, weight changes, food preparation, and diets. The criterion for diagnosis is based on 64 scores in the questionnaire. If the elderly got scores less than 50, they are prone to malnutrition; scores of less than 43 indicate moderate malnutrition, and scores of less than 38 indicate severe malnutrition. Amini et al. investigated the validity and reliability of this questionnaire in the study of older people in Iran [25]. In the present study, the Cronbach α of the questionnaire was reported 0.87.
 To collect data after the necessary coordination, the health centers of Tabriz prepared a list of the names of the elderly. They were randomly selected using a table of random numbers and invited to participate in the study by phone. After obtaining written consent from the elderly, the study data were collected through questionnaires obtained from literate seniors or through trained questioners by reading the questions for the elderly and insert their answers based on the available options in the questionnaire.
To describe the data, absolute and relative frequency distribution indices, mean and standard deviation were used. The Shapiro-Wilk test was used to check the normality of the data. Finally, simple and multiple linear regression analyses were used to evaluate the relationship between variables and control the effect of intervention variables. Based on the leading method, the variables are entered into the model. SPSS version 26 was used to analyze the collected data. Finally, a significance level was considered for all analyzes (P<0.05).
Results
In this study, 300 older people aged 60 years and older living in Tabriz City, Iran, with an Mean±SD age of 69.7±6.7 years under the auspices of urban health centers participated. Other demographic information is reported in Table 1.


Frequency distribution of oral health status, health literacy level, and nutritional status among the elderly under study showed that the Mean±SD score of oral health was 40.68±5.66, and oral health status was 153(51%) lower than the average for the elderly. One hundred and ninety-six patients (65.33%) had insufficient health literacy level, and the Mean±SD score of health literacy was 43.12±19.64 and 208 patients (69.33%) were severely malnourished. Only 11 patients (3.67%) did not suffer from malnutrition or were not exposed to malnutrition.
To investigate the relationship between demographic factors, nutritional status, and health literacy with oral health, we used linear regression (Table 2).


The results of linear regression analysis indicate that gender and marital status did not predict the oral health score, while age was a significant variable in predicting the oral health of the elderly. In other words, the oral health score is expected to decrease by 1.2 units for every 10 years of age. Also, with increasing the level of education of the elderly, the oral health status was significantly better. Nutritional status was also a significant predictor of oral health. It is expected that for people with severe malnutrition, the oral health score is 13.6 units lower than for people with healthy nutrition. Adequate and excellent health literacy level was also a predictor of oral health, so it is expected that for people with sufficient and excellent health literacy level, oral health score is 3.26 units higher than people with inadequate literacy level. But when the multiple linear regression model was fitted to the data, only nutritional status significantly predicted oral health. The oral health score of people with severe malnutrition was 13.5 points lower than people with healthy nutrition. The coefficient of determination of the multiple regression model is equal to 0.59; in other words, the studied variables could explain 59% of the changes in the response variable. The results related to multiple regression are reported in Table 3.


Discussion
This study aimed to determine the relationship between oral health and health literacy and nutrition among the elderly in Tabriz. The study results showed that the oral health status of people who are exposed to malnutrition or suffer from moderate and severe malnutrition is lower than mean. The mutual relationship between oral health status and malnutrition, as well as diet status and its impact on oral health, have been shown in different studies and different groups [16, 26]. Ziebolz et al. multivariate analysis showed that edentulousness was significantly associated with malnutrition [27]. Teeth loss affects the selectivity, preparation, consumption, and nutritional status of the elderly [28]. Also, teeth loss and chewing disorders are associated with limited consumption of various foods (especially fruits and vegetables), increased consumption of sweet and chewy foods, and less consumption of fiber and vitamins in the diet [29]. In a study of the adult population, it was found that two-thirds of the participants consumed sugary drinks and snacks between meals [15], which endangers their oral health. The Mthethwa’s study showed that eating an unhealthy diet predicts tooth decay and its health [30].
In the present study, the oral health status of more than half of the subjects was below mean. In the study of Ahmadi et al. on a sample of older people in Tehran City, Iran, 24% of the participants had poor oral health status [20]. Khatami Nasab’s study reported that the oral health status of the elderly covered by the Welfare Organization was very unsatisfactory. In this study, the oral health questionnaire of the World Health Organization was used [31]. Poor oral health is associated with various diseases such as diabetes, cardiovascular and cognitive impairment, and mental health illnesses [32, 33]. In justifying the poor oral health status of the elderly, we can mention economic factors, access to oral care services, nutritional status, and health status of the elderly [34, 35].
The study results showed that the health literacy status of most of the elderly understudy is poor and inadequate. Our study results are consistent with the study results of Mir Mohammadkhani et al. [13]. Restrictions on health literacy increase with age [36]. Also, increasing age may cause cognitive and perceptual problems in the elderly, which can be an obstacle to obtaining information and increasing the health literacy of the elderly [37]. The research results by Lee et al. showed a relationship between good oral health literacy and a healthier and better oral health status [38]. In our study, no correlation was seen after the adjustment of variables. Still, in the simple linear regression model, a relationship was found between oral health status and oral health literacy. In justifying this finding, we can point to different studied societies, the level of literacy of the people under study, and study tools. In lee study [38], the Carolina oral health literacy questionnaire was used to assess health literacy status. However, in both studies, the health literacy of the elderly is low.
Another factor related to oral health status is education. Based on linear regression, people with higher education have better oral health. Having education leads to more access to information about oral health or care and see a dentist [30]. Oral health status and performing behaviors that promote oral health among women are better than men in some studies [35]. In the study of Ahmadi et al., the oral health status of men was better than women [20], which may be related to the physical condition of women, pregnancy, and childbirth.
Based on the results of multiple regression and fitted model, no significant relationship was observed between demographic information and oral health. These results contradict the results of Ahmadi et al. [20] and Mthethwa et al. [30], which showed the relationship between demographic characteristics such as age, sex, and educational status with oral health. Oral health may decrease with age due to diseases such as diabetes and cognitive problems. Also, this age group is involved in several general health problems, and therefore oral health is probably less of a priority for them. Coordinating and receiving dental services depends on other people, and they are not aware of many consequences of oral diseases and how to prevent them [39].
This study also had some limitations. The study’s cross-sectional nature did not allow understanding the cause-and-effect relationship between the variables. Also, data collection was self-reported, which may not have reflected the actual performance of individuals. There are also many variables, such as economic status, that may affect oral health and have not been studied in the present study, so it is recommended to be considered in future studies. Because of the relationship between nutritional status and oral health, it is recommended that interventional studies be conducted to improve the nutritional status of the elderly and its relationship with the oral health of this group of society.

Ethical Considerations
Compliance with ethical guidelines
To observe the ethical principles in the research, the study’s objectives were explained to the participants. After assuring them that the obtained information was confidential and the results were published in general, and the questionnaires were anonymous, written consent was obtained from the participants in the study. This research was conducted after receiving the ethical code number IR.TBZMED.REC.2019.221 from the Ethics Committee of Tabriz University of Medical Sciences.

Funding
This research with code 62468 is under the financial support of the Vice-Chancellor for Research and Technology of Tabriz University of Medical Sciences.

Author's contributions
Conception and design of the study: Shahab Papi and Zeynab Karimi; Analysis and interpretation of data: Zahra Taheri-Kharameh, Fatemeh Hosseini, and Zeynab Karimi; Collection, assembly, possession of raw data: Manijeh Izadi, Leila Behboodi, and Mahdi Yousefi; Critical revision: Shahab Papi; Final approval of the study: All authors.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
The authors consider it necessary to thank and appreciate all the elderly participants, the officials of health centers, and the Vice-Chancellor for Research and Technology of Tabriz University of Medical Sciences.


References

1. Papi S, Karimi Z, Saadat Talab F, Hosseini F, Afrouzeh H, Yousefi M, et al. Relationship between health literacy and multi-infections based on gender differences in the elderly. Health Education and Health Promotion. 2021; 9(2):105-10. https://iranjournals.nlai.ir/handle/123456789/813348
2. Papi S, Cheraghi M. Relationship between life satisfaction and sleep quality and its dimensions among older adults in city of Qom, Iran. Social Work in Public Health. 2021; 36(4):526-35. [DOI:10.1080/19371918.2021.1917466] [PMID]
3. Raphael C. Oral health and aging. American Journal of Public Health. 2017; 107(S1):S44-5. [DOI:10.2105/AJPH.2017.303835] [PMID] [PMCID]
4. Pournaghi-Azar F, Asl-Aminabadi N, Jamali Z, Azami A, Hazem K, Azami-Aghdash S, et al. Status of decayed, missing, filled teeth index among Iranian children and adults: A systematic review and meta-analysis. Journal of Research in Clinical Medicine. 2018; 6(2):55-66. [DOI:10.15171/jarcm.2018.009]
5. Nazir MA. Prevalence of periodontal disease, its association with systemic diseases and prevention. International Journal of Health Sciences. 2017; 11(2):72-80. [PMCID]
6. Papi S, Karimi Z, Ghaed Amini Harooni G, Nazarpour A, Shahry P. [Determining the prevalence of sleep disorder and its predictors among elderly residents of nursing homes of Ahvaz city in 2017 (Persian)]. Salmand: Iranian Journal of Ageing. 2019; 13(5):576-87. [DOI:10.32598/SIJA.13.Special-Issue.576]
7. Balanian S, Mirzaee M, Jambarsang S, Hosseini SAS. [Oral health of elderly people in Yazd city and its relationship with quality of life (Persian)]. Journal of Dental Medicine. 2019; 32(3):171-6. https://www.cabdirect.org/globalhealth/abstract/20203395740
8. Papi S, Abolfathi Momtaz Y, Foroughan M, Mohammadi Shahboulaghi F, Araban M, Ramezani T. Comparing the effect of face-to-face education and E-learning on the physical activity of the elderly. Journal of Holistic Nursing and Midwifery. 2021; 31(1):35-43. [DOI:10.32598/jhnm.31.1.2037]
9. Khanemasjedi M, Araban M, Mohamadinia M. [Relationship between malocclusion and oral health-related quality of life among high school students (Persian)]. Journal of Education and Community Health. 2018; 5(1):27-35. [DOI:10.21859/jech.5.1.27]
10. Motallebnejad M, Mehdizadeh S, Najafi N, Sayyadi F. The evaluation of oral health-related factors on the quality of life of the elderly in Babol. Contemporary Clinical Dentistry. 2015; 6(3):313-7. [DOI:10.4103/0976-237X.161867] [PMID] [PMCID]
11. Panahi R, Ebrahimi G, Ahmadi A. [Health literacy: A key component of controlling social determinants of health (Persian)]. Journal of Education and Community Health. 2018; 5(1):1-3. [DOI:10.21859/jech.5.1.1]
12. Panagioti M, Skevington SM, Hann M, Howells K, Blakemore A, Reeves D, et al. Effect of health literacy on the quality of life of older patients with long-term conditions: A large cohort study in UK general practice. Quality of Life Research. 2018; 27(5):1257-68.. [DOI:10.1007/s11136-017-1775-2] [PMID] [PMCID]
13. Mirmohammadkhani M, Ziari A, Momeni M. [Systematic review and meta-analysis of health literacy in Iranian older adults (Persian)]. Salmand: Iranian Journal of Ageing. 2020; 15(1):2-13. [DOI:10.32598/sija.2020.3.210]
14. Papi S, Karimi Z, Zilaee M, Shahry P. Malnutrition and its relation to general health and multimorbidity in the older people. Journal of Holistic Nursing and Midwifery. 2019; 29(4):228-35. [DOI:10.32598/JHNM.29.4.228]
15. Payahoo L, Khaje-bishak Y, Gargari BP, Kabir-alavi M-b, Jafarabadi MA. [Nutritional status and its relation with depression in free-living elderly individuals (Persian)]. Medical Journal of Tabriz University of Medical Sciences & Health Services. 2013; 35(5):20-5. https://mj.tbzmed.ac.ir/Article/8841
16. Sistani MMN, Virtanen JI, Yazdani R, Murtomaa H. Association of oral health behavior and the use of dental services with oral health literacy among adults in Tehran, Iran. European Journal of Dentistry. 2017; 11(2):162-7. [DOI:10.4103/ejd.ejd_332_16] [PMID] [PMCID]
17. Holtzman JS, Atchison KA, Gironda MW, Radbod R, Gornbein J. The association between oral health literacy and failed appointments in adults attending a university- based general dental clinic. Community Dentistry and Oral Epidemiology. 2014; 42(3):263-70. [DOI:10.1111/cdoe.12089] [PMID] [PMCID]
18. Saied Moallemi Z, Haghighi M. [Assessing oral health literacy among the residents of Isfahan in 2014-2015 (Persian)]. J Isfahan Dent Sch. 2016; 12(3):268-79. https://www.sid.ir/en/Journal/ViewPaper.aspx?ID=529040
19. Nezafati A, Mokhtari Lake N, Sheikholeslami F, Kazemnezhad Leili E. Health literacy and its related factors among the elderly in Rasht city, Iran. Journal of Holistic Nursing and Midwifery. 2020; 30(3):129-36. [DOI:10.32598/jhnm.30.3.1053]
20. Ahmadi A, Sahaf R, Rashedi V, Akbari Kamrani AA, Shati M, Delbari A. [Relationship between oral health and demographic characteristics in retired elderly people in Iran (Persian)]. Salmand: Iranian Journal of Ageing. 2019; 13(4):452-63. [DOI:10.32598/SIJA.13.4.452]
21. Montazeri A, Tavousi M, Rakhshani F, Azin SA, Jahangiri K, Ebadi M, et al. [Health Literacy for Iranian Adults (HELIA): Development and psychometric properties (Persian)]. Payesh (Health Monitor). 2014; 13(5):589-99. http://payeshjournal.ir/article-1-279-en.html
22. Atchison KA, Dolan TA. Development of the geriatric oral health assessment index. Journal of Dental Education. 1990; 54(11):680-7. [DOI:10.1002/j.0022-0337.1990.54.11.tb02481.x] [PMID]
23. Rezaei M, Rashedi V, Khedmati Morasae E. A Persian version of geriatric Oral health assessment index. Gerodontology. 2016; 33(3):335-41. [DOI:10.1111/ger.12161] [PMID]
24. Keller HH, Goy R, Kane SL. Validity and reliability of SCREEN II (Seniors in the community: risk evaluation for eating and nutrition, Version II). European Journal of Clinical Nutrition. 2005; 59(10):1149-57.‏ [DOI:10.1038/sj.ejcn.1602225] [PMID]
25. Amini F. [Investigating validity & reliability of nutrition status of screen II questionner among iranian olde (Persian)]. Tehran: University of Social Welfare and Rehbilitation Sciences; 2017. https://lib.uswr.ac.ir/site/catalogue/70496
26. Jahangiry L, Bagheri R, Darabi F, Sarbakhsh P, Sistani MMN, Ponnet K. Oral health status and associated lifestyle behaviors in a sample of Iranian adults: An exploratory household survey. BMC Oral Health. 2020; 20(1):82. [DOI:10.1186/s12903-020-01072-z] [PMID] [PMCID]
27. Ziebolz D, Werner C, Schmalz G, Nitschke I, Haak R, Mausberg RF, et al. Oral health and nutritional status in nursing home residents-results of an explorative cross-sectional pilot study. BMC Geriatrics. 2017; 17(1):39. [DOI:10.1186/s12877-017-0429-0] [PMID] [PMCID]
28. Petrovski M, Terzieva-Petrovska O, Dimova C, Minovska A, Papakoca K, Zlatanovska K. Correlation of oral health and diet among institutionalized elderly people. Journal of Hygienic Engineering and Design. 2020; 31:116-21. https://eprints.ugd.edu.mk/24189/
29. Kossioni AE. The association of poor oral health parameters with malnutrition in older adults: A review considering the potential implications for cognitive impairment. Nutrients. 2018; 10(11):1709. [DOI:10.3390/nu10111709] [PMID] [PMCID]
30. Mthethwa J, Mahomed O. Predictors of dental caries among adults attending public oral health facilities in two districts in KwaZulu-Natal, South Africa: A cross sectional study. Research Square. 2020. [DOI:10.21203/rs.3.rs-61069/v1]
31. Khatmi Nasab N, Shamshiri M, Zamani U. [The study of oral health status and its related quality of life in elderly people supported by welfare organization in Ardabil city (Persian)]. Journal of Health and Care. 2019; 21(4):308-18. [DOI:10.29252/jhc.21.4.308]
32. Khoshnevisan M, Ghasemianpour M, Samadzadeh H, Baez R. Oral health status and healthcare system in IR Iran. Journal of Contemporary Medical Sciences. 2018; 4(3):107-18. [DOI:10.22317/jcms.09201801]
33. Liljestrand J, Havulinna A, Paju S, Männistö S, Salomaa V, Pussinen P. Missing teeth predict incident cardiovascular events, diabetes, and death. Journal of Dental Research. 2015; 94(8):1055-62. [DOI:10.1177/0022034515586352] [PMID]
34. Guo Y, Logan HL, Dodd VJ, Muller KE, Marks JG, Riley 3rd JL. Health literacy: A pathway to better oral health. American Journal of Public Health. 2014; 104(7):e85-91. [DOI:10.2105/AJPH.2014.301930] [PMID] [PMCID]
35. Cepova E, Cicvakova M, Kolarcik P, Markovska N, Geckova AM. Associations of multidimensional health literacy with reported oral health promoting behaviour among Slovak adults: A cross-sectional study. BMC Oral Health. 2018; 18(1):44. [DOI:10.1186/s12903-018-0506-6] [PMID] [PMCID]
36. Kobayashi LC, Wardle J, Wolf MS, Von Wagner C. Aging and functional health literacy: A systematic review and meta-analysis. Journals of Gerontology Series B: Psychological Sciences and Social Sciences. 2016; 71(3):445-57. [DOI:10.1093/geronb/gbu161] [PMID] [PMCID]
37. Nguyen HT, Kirk JK, Arcury TA, Ip EH, Grzywacz JG, Saldana SJ, et al. Cognitive function is a risk for health literacy in older adults with diabetes. Diabetes Research and Clinical Practice. 2013; 101(2):141-7. [DOI:10.1016/j.diabres.2013.05.012] [PMID] [PMCID]
38. Lee JY, Divaris K, Baker AD, Rozier RG, Vann Jr WF. The relationship of oral health literacy and self-efficacy with oral health status and dental neglect. American Journal of Public Health. 2012; 102(5):923-9. [DOI:10.2105/AJPH.2011.300291] [PMID] [PMCID]
39. Kosari M, Hoseini Z, Golrizi F. [The investigation of oral and dental status and its related factors in the elderly in Torbat Heydariyeh in 2015 (Persian)]. Journal of Torbat Heydariyeh University of Medical Sciences. 2016; 4(2):39-44. https://www.sid.ir/en/journal/ViewPaper.aspx?ID=521210