Dietary Antioxidant Index and the Risk of Recurrent Aphthous Stomatitis

Abstract

Background

Recurrent aphthous stomatitis (RAS) is a common condition that affects the oral mucosa. Antioxidants are crucial in neutralizing free radicals in the body and may have a preventive role against RAS. This study aims to examine the association between dietary antioxidant index (DAI) and RAS occurrence.

Methods

This cross-sectional study was conducted on 144 individuals with RAS and 135 individuals without RAS. The dietary intake of the participants was assessed using the food frequency questionnaire. The DAI was applied to measure the antioxidant capacity of the diet. Logistic regression models were applied to assess the link between RAS and DAI after adjusting the confounding variables.

Results

There was a significant negative association between RAS and DAI of zinc (OR = 0.639, CI95%: 0.456-0.896, P = .009) and total score of DAI (OR = 0.802, CI95%: 0.682-0.944, P = .008) after adjustment for age. The results remained significant after further adjustment for body mass index and calorie intake.

Conclusion

The present study indicated a possible negative association between the risk of RAS and the DAI score as a measure of the antioxidant potential of diet. Further studies are warranted.

Introduction

Recurrent aphthous stomatitis (RAS), also known as recurrent oral ulceration, is a common condition characterized by the repeated formation of benign mouth ulcers.^1,2 There are three clinical classifications of RAS including minor (MiRAS), which is the most prevalent form of RAS and occurs in 75% to 80% of the patients, major (MaRAS), and herpetiformis ulcers.^3,4 RAS prevalence ranges from 5% to 50%, with an average of 20% and a higher rate in young women⁵ and may persist for a lifetime.⁶ In the Iranian population, the rate of occurrence was estimated to be high in the range of 20% to 26%.^7,8

Various potential triggers for RAS have been identified including genetics, trauma, smoking, nutritional deficits, infections, stress, hormonal shifts, blood disorders, allergies, immune system function, and diet. Although the exact aetiology of RAS is still uncertain,^9,10 a negative association was found between healthy diet and fruit intake with RAS occurrence.¹¹ The consumption of fruits, which account for about 50% of dietary antioxidants, may be protective against RAS.¹⁰ Additionally, the adverse effects of spicy and fried foods^12,13 and certain food allergens in RAS are previously reported.^14,15

RAS may be caused by disruption of the body's oxidative balance, increasing free radicals and oxidative stress.¹⁶ Some investigations reported the effect of oxidative stress on RAS and indicated that there is a higher level of oxidative stress, impaired antioxidant defense^17,18 and lower levels of serum antioxidant enzyme activity in patients with RAS.¹⁹ Antioxidants are vital in preventing oxidative damage by neutralizing free radicals in the body.²⁰ Antioxidants in foods are present as either free (eg, vitamins C and E, carotenoids, and some polyphenols) or bound to complex food components (eg, high-molecular-weight polyphenols bound to dietary fibres, proteins, and lipids).^21,22 Patients with RAS were reported to have lower blood and saliva levels of vitamins A, E, and C than the healthy people.^23,24 Although most studies examined the role of dietary antioxidants separately, the association of RAS with the overall antioxidant potential of the diet has been less studied. The dietary antioxidant index (DAI) is a validated nutritional tool to evaluate the antioxidant capacity of diets and is calculated based on the intake of major dietary antioxidants including vitamin A, vitamin C, vitamin E, selenium, manganese, and zinc.^25,26 Due to the established relationship between RAS and oxidative stress, and the lack of comprehensive research on the impact of total antioxidant capacity of diet on RAS, this study aimed to examine the association between DAI and the risk of RAS.

Methods

Study design

This cross-sectional study was carried out on 150 females with RAS and 150 females without RAS who were referred for general checkups to Shahadaye Tajrish Hospital, Tehran, Iran. Based on the World Health Organization, a well-demarcated yellow-white painful ulcer with the peripheral erythematous halo was recognized as RAS.²⁷ The diagnosis of RAS was approved based on the history of recurrent oral ulcers and clinical presentation criteria including the type and characteristics of the ulcers (minor, major, or herpetiform), their size, depth, duration, location within the oral cavity, healing pattern, and presence or absence of scarring diagnosed by a dentist. The present study was performed in young females since the onset of RAS was reported to be highest in this population.⁶ The sample size was calculated using the Open EPI online software and the odds ratio obtained in a similar previous study.¹¹ The inclusion criteria were written consent, female gender, and age between 35 and 70 years. Exclusion criteria included inability to collect information, unwillingness to continue participating in the study, the history of activities and diseases affecting the development of mouth ulcers including minor damage to the mouth due to dental interventions, brushing too hard, sports injuries, accidentally biting the inside of the cheek, using mouthwashes containing sodium lauryl sulphate (determined through patient self-reporting and verification of their toothpaste ingredients), food sensitivities, especially to chocolate, coffee, strawberries, eggs, nuts, cheese, and spicy or acidic foods, diseases such as helicobacter pylori infection, celiac disease, inflammatory bowel disease, acquired immunodeficiency syndrome, hormonal changes during menstruation, and emotional stress (assessed using the perceived stress scale or PSS).²⁸ The final analysis was conducted on 144 women with RAS and 135 women without RAS.

Data collection

Data were gathered using a self-administered questionnaire covering general information such as age, place of residence, lifestyle habits, disease history, medication use, and smoking status. Participants’ weight was measured using a Seca digital scale with 0.1 kg accuracy, and height was measured with a tape measure to the nearest 0.1 centimetre. Body mass index (BMI) was calculated accordingly, dividing weight (kg) by the square of height (meters). A validated form of International Physical Activity Questionnaire was employed for assessing the level of physical activity.²⁹

Dietary intake evaluation

Food intake was assessed using a validated food frequency questionnaire (FFQ) questionnaire which was reported to have acceptable validity and reliability in the Iranian population³⁰ and consists of 168 different food items and was completed in order to achieve the usual diet of a person. The FFQ can estimate the average daily consumption of different nutrients such as antioxidants. The information collected by the FFQ was converted to grams per day and was transferred to modified Nutritionist IV version 4.1 software to assess Iranian foods (First Databank Division, The Hearst Corporation). Then, the DAI was used to evaluate the antioxidant capacity of the diet, incorporating vitamins A, C, E, manganese, selenium, and zinc. The DAI score was calculated by standardized each of vitamins A, C, E, and selenium, manganese, and zinc by subtracting the global mean and dividing by the global standard deviations (SD). The antioxidant profile of the diet was evaluated in both quantitative and categorical ways. In the categorical method, considering that a specific DAI cut-off has not yet been determined, the median index of the collected data is used as a cut-off.

Statistical analysis

Data analysis was performed using the Statistical Package for Social Sciences software (version 27), with a significance level set at P < .05. Descriptive statistics such as mean and SD were used for quantitative data, while numbers and percentages were used for qualitative data. Chi-squared test and independent t test methods were used to compare the qualitative and quantitative variables between females with and without RAS, respectively. Logistic regression modelling was applied to adjust for the confounding variables, with the presence of RAS as the dependent variable and DAI as the independent variable.

Results

Based on the information presented in Table 1, participants without RAS had lower age (48.66 ± 8.07 vs 50.78 ± 8.55, P = .034) and higher BMI (29.48 ± 4.62 vs 27.99 ± 3.42, P = .003) than females with RAS.

Table 1.

General characteristics of the participants.

		Females without RAS (n = 135)	Females with RAS (n = 144)	P
Age (y)		48.66 ± 8.07	50.78 ± 8.55	.034
Height (cm)		156.31 ± 5.48	155.93 ± 6.17	.593
Weight (kg)		72.05 ± 12.00	68.30 ± 10.70	.006
BMI (kg/m2)		29.48 ± 4.62	27.99 ± 3.42	.003
Physical activity (h/d)		1.57 ± 1.60	1.52 ± 1.47	.821
Diabetes history	No	124 (53.4%)	108 (46.6%)	.148
	Yes	19 (41.3%)	27 (58.7%)
	Yes	45 (61.6%)	28 (38.4%)
Occupied	No	90 (43.9%)	115 (56.1%)	.226
	Yes	45 (61.6%)	28 (38.4%)
Marital state	Married	123 (91%)	129 (95%)	.148
	Single	12 (9%)	14 (5%)

BMI, body mass index; RAS, recurrent aphthous stomatitis.

Regarding the intake of dietary antioxidants, based on Table 2, women without RAS had a higher intake of zinc (12.01 ± 4.14 vs 10.94 ± 4.64 mg/d, P = .043) and a lower intake of vitamin C (182.29 ± 115.83 vs 243.68 ± 193.28 mg/d, P = .003) compared to females with RAS. However, both groups received above the Recommended Dietary Allowance of 75 mg/d for vitamin C in adult women. Regarding the DAI scores, the mean DAI of vitamin C was significantly lower (–0.19 ± 0.72 vs 0.2 ± 1.20, P = .003) and the mean DAI of zinc was significantly higher (0.12 ± 0.94 vs –0.12 ± 1.05, P = .043) in females without RAS compared to the females with RAS.

Table 2.

Dietary intake of the participants.

	Females without RAS (n = 135)	Females with RAS (n = 144)	P
Energy (kcal/d)	2571.67 ± 406.28	2607.05 ± 395.82	.463
Protein (g/d)	84.02 ± 19.48	84.00 ± 19.25	.995
Carbohydrate (g/d)	367.51 ± 64.65	372.98 ± 58.25	.460
Total fat (g/d)	93.53 ± 18.43	94.07 ± 22.45	.825
Vitamin A (mcg/d)	656.32 ± 352.47	715.84 ± 415.97	.200
Vitamin C (mg/d)	182.29 ± 115.83	243.68 ± 193.28	.003
Vitamin E (mg/d)	19.03 ± 8.50	18.57 ± 10.39	.683
Manganese (mg/d)	407.03 ± 110.09	399.93 ± 92.46	.562
Zinc (mg/d)	12.01 ± 4.14	10.94 ± 4.64	.043
Selenium (mcg/d)	100.07 ± 36.83	101.50 ± 35.52	.743
DAI of vitamin A	–0.08 ± 0.91	0.08 ± 1.08	.200
DAI of vitamin C	–0.19 ± 0.72	0.2 ± 1.20	.003
DAI of vitamin E	0.02 ± 0.90	–0.03 ± 1.10	.683
DAI of selenium	–0.02 ± 1.02	0.02 ± 0.98	.743
DAI of manganese	0.01 ± 1.12	–0.02 ± 0.86	.800
DAI of zinc	0.12 ± 0.94	–0.12 ± 1.05	.043
Total DAI	–0.14 ± 3.09	–0.06 ± 3.20	.841

DAI, dietary antioxidant index; RAS, recurrent aphthous stomatitis.

Regarding the association between RAS and DAI (Table 3), there was a significant inverse association between the risk of RAS and DAI of zinc (OR = 0.639, CI95%: 0.456-0.896, P = .009) and total DAI (OR = 0.802, CI95%: 0.682-0.944, P value = .008) after adjustment for age. After further adjusting for BMI and calorie intake, the results on the association of RAS and zinc (OR = 1.64, CI95%: 0.45-0.90, P value = .011) and total DAI score (OR = 0.76, CI95%: 0.62-0.93, P value = .008) remained significant.

Table 3.

Logistic regression of the association of recurrent aphthous stomatitis (RAS) and dietary antioxidant index (DAI).

	Model 1		Model 2
	OR (CI95%)	P	OR (CI95%)	P
Vitamin A	1.190 (0.909-1.548)	0.209	1.222 (0.929-1.608)	.151
Vitamin C	1.381 (0.995-1.929)	0.054	1.373 (0.975-1.933)	.069
Vitamin E	0.932 (0.685-1.271)	0.632	0.970 (0.70-1.34)	.844
Selenium	1.054 (0.832-1.335)	0.665	1.012 (0.772-1.328)	.929
Manganese	0.670 (0.449-1.001)	0.051	0.691 (0.460-1.051)	.085
Zinc	0.639 (0.456-0.896)	0.009	0.635 (0.451-0.901)	.011
Total DAI	0.802 (0.682-0.944)	0.008	0.761 (0.621-0.935)	.008

Model 1: adjusted for age, Model 2: further adjustments for BMI and calorie intake.

Discussion

The present study highlighted an inverse association between total dietary antioxidant potential and the risk of RAS after adjusting the confounding factors. Previous studies reported that patients with RAS have higher levels of oxidative stress indicators and lower levels of antioxidant biomarkers than healthy people.³¹ However, the results of the studies conducted on the effect of nutrients with antioxidant properties in RAS patients are contradictory. One of the weak points of the previous studies is not paying attention to the synergistic effects of antioxidants on each other, which can be involved in obtaining these conflicting results. The present study applied the DAI as a measure to evaluate the antioxidant capacity of the diet against RAS, which includes various antioxidants such as vitamins A, C, and E, as well as manganese, selenium, and zinc.

In the pathogenesis of RAS, oxidative stress is one of the most frequently studied factors.³² Oxidative stress forms when the balance between oxidants and antioxidants shifts towards oxidative status. Antioxidants reduce oxidative stress by neutralizing reactive oxygen species and other free radicals, which are key contributors in the development of RAS. This reduction in oxidative stress subsequently inhibits the activation of nuclear factor kappa B and other inflammatory pathways, leading to a lower risk of RAS through a decrease in the production of pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6.³³ Furthermore, antioxidants promote tissue repair in RAS by supporting cellular repair and maintaining the integrity of the oral mucosal barrier, which is essential for healing.³⁴ Few studies have been conducted regarding the relationship between dietary antioxidants and RAS. In line with the present study, a cross-sectional study in China found a significant negative relationship between fruit consumption as one of the best sources of antioxidants and the risk of RAS.¹¹ A laboratory study on rats showed that zinc deficiency in the diet affects oral mucosa and periodontal status.³⁵ Furthermore, patients with RAS were reported to have lower serum zinc levels compared to healthy individuals and the role of zinc in the inhibition of free radicals and the treatment of RAS was suggested.¹¹ Zinc has been suggested to play a role in wound healing by improving the immune system and collagen synthesis.³⁶ On the contrary, in the study of Ślebioda et al,³⁵ no significant difference was found between serum levels of zinc in patients with RAS and healthy individuals. Furthermore, Khademi et al³⁷ did not find a significant relationship between the serum levels of vitamins A, C, and E between the RAS and healthy groups. In the present study, the dietary intake of zinc was investigated and not the serum level of zinc. The reason for the difference in the obtained results may be that the serum level of zinc is not a good indicator for the protective effects of zinc against RAS.

Regarding other dietary antioxidants, the present study found that the intake of vitamin C in people with RAS was higher than in non-afflicted people. Although both groups received higher than the recommended amount of vitamin C for adult women (75 mg/d). High amounts of vitamin C may have an adverse effect on RAS due to its acidic nature. A recent study indicated that acidic dietary components may have a role in the aetiology of RAS.³⁸ A systematic review study in 2022 showed that RAS patients were deficient in vitamin E. However, no deficiency was found in terms of zinc and vitamin C.³⁹ In another study, Ogura et al reported that patients with RAS have lower intake levels of vitamin C than healthy individuals.²⁴ Another study observed that the serum levels of selenium in RAS patients were found to be lower than in the healthy group.⁴⁰ However, these studies examined the serum levels of antioxidant substances and their dietary intake has not been measured. While the difference in the method of assessing these vitamins can be the reason for the difference in these results, the synergistic effect of antioxidants should not be ignored, which is one of the strengths of the present study which applied the DAI score to consider the combined effect of total antioxidants.⁴¹ It is plausible that the use of the DAI may fill the gap created by the contradictory results of the previous studies on the relationship between vitamins and minerals with antioxidant properties and the risk of RAS. However, the present study had some limitations. First, the evaluation of dietary intake using FFQ may be affected by measurement errors and recall bias. Second, the cause-and-effect relationship cannot be proven in this cross-sectional study. Third, the frequency of using toothpaste and mouthwashes was not investigated in this study which may be effective on the incidence of RAS. Fourth, data on different types of RAS was not collected and sub-group analyses were not possible. Future studies that address these limitations are necessary to obtain a definitive conclusion on the relationship between the risk of RAS and dietary antioxidants.

Conclusion

The present study indicated a possible inverse association between the risk of RAS and the overall DAI score and the DAI score of zinc. Our study highlights the potential benefit of the DAI, instead of assessing separate antioxidants which may have a variety of different effects on the risk of RAS. If this is confirmed in future studies, recommending a diet with a high DAI score may be considered a protective factor against RAS. Further longitudinal studies are warranted to confirm the obtained results on the association between DAI and the risk of RAS and to discover the underlying mechanisms.

Conflict of interest

The authors explicitly state that they possess no conflicts of interest.