Relationship between body mass index and dental caries in children, and the influence of socio-economic status

Abstract

Objectives: To determine the association of body mass index (BMI) with dental caries in Indian schoolchildren, and to analyse the influence of socio-economic status (SES). Methods: The study population consisted of 11- to 14-year-old children from Medak District in Telangana State, India. The Indian Academy of Paediatrics 2015 growth charts were used to categorise children as underweight, overweight, normal or obese, based on their BMI. Data on the SES of the family were collected through questionnaires. Clinical examination for dental caries was performed by a single examiner. Results: A total of 1,092 subjects returned questionnaires and were clinically examined (giving a response rate of 85%). There were no significant differences in caries prevalence and experience across the categories of BMI. However, caries prevalence and experience in overweight children were 24.8% and 0.69 ± 1.51, respectively, while the corresponding values in normal-weight children were 35% and 0.85 ± 1.50, respectively. Among children of high-SES families, overweight children had approximately 71% fewer caries than did those who were normal weight [incidence rate ratio (IRR) = 0.29; 95% CI: 0.11–0.78)]. Conclusions: BMI was not associated with dental caries prevalence and experience in this population. The association of BMI with dental caries varied across SES categories. In the high-SES category, overweight children experienced fewer caries than did normal-weight children.

Introduction

Dental caries is the most prevalent health condition in the world1., 2.. Globally, it affects 2.4 billion people² and the economic burden of treating dental diseases accounts for 4.6% of global health expenditure³. Dental caries, like most other chronic multifactorial diseases, is influenced by numerous genetic, environmental and behavioural risk factors4., 5.. Dental caries is predicted by many factors that range from population-level variables to individual circumstances. Among many factors, nutritional status has also long been associated with oral diseases⁶. Under-nutrition is associated with enamel hypoplasia and salivary gland atrophy which increases the risk of dental caries, and the effect of this is pronounced during the pre-eruptive stages of tooth development⁷. On the other hand, over-nutrition, manifesting as obesity, has also been associated with dental caries⁸. The association of obesity with dental caries is not necessarily causal and is complicated by many intervening variables9., 10.. Nevertheless, both of these chronic diseases (obesity and dental caries) share common influences, such as diet and lifestyle, and genetic and socio-economic factors10., 11..

Evidence of the association of nutrition status with dental caries is inconsistent. A recently published systematic review found that approximately half of the studies published between 2004 and 2011 found no association between body mass index (BMI) and dental caries, while one-third of the studies found positive associations and the remaining an inverse relationship¹¹. These inconsistencies may be caused by differences in study design, study location⁸, methods of assessment of nutritional status and of dental caries, and the age of the participants and their socio-economic background¹². Hayden et al., in their systematic review, reported that high BMI is associated with high caries experience in developed, industrialised, countries but not in developing, newly industrialised, countries such as Brazil, India and Thailand⁸.

There are no studies from India that have assessed the association of BMI and dental caries in relation to socio-economic status (SES). Therefore, the aim of this study was to determine the association of BMI with dental caries in Indian schoolchildren, and to analyse the influence of SES.

Methods

Study population

The study population consisted of 11- to 14-year-old schoolchildren of Medak district in Telangana State, India. Representative children were recruited from schools using a multistage sampling technique. In the first stage, eight subdistricts of Medak district, from a total of 46, were randomly selected. This was followed by randomly selecting schools, the number of which was proportional to the total number of schools in that subdistrict. Lastly, all sixth-grade children in each selected school were invited to participate.

Procedure

Children whose parents provided written consent for their participation underwent a dental examination, weight and height measurements and also responded to a questionnaire. The height of each child, without shoes, was recorded to the nearest 0.1 cm using a portable height meter with a horizontal headboard on a flat surface. Weight was measured using a portable balance to the nearest 100 g¹³. BMI for each individual was calculated as weight divided by squared height in metres. Height-for-age (HAZ), weight-for-age (WAZ) and BMI-for-age (BAZ) scores were calculated, using the revised Indian Academy of Paediatrics (IAP) 2015 growth charts for ages 5–18 years as a reference¹⁴. These Z scores specific to age and gender were generated using Microsoft Excel, which was provided by the authors of the revised IAP growth charts¹⁴. Subjects were categorised as underweight, normal, overweight and obese based on the BAZ cut-offs proposed by the IAP. The cut-off for underweight in all the children was −1.88; boys and girls with BAZ values of ≥0.55 and ≥0.67, respectively, were considered overweight. Boys and girls with BAZ values of ≥1.34 and ≥1.64, respectively, were considered obese.

Clinical examination for dental caries was performed by a single examiner (S.K.). Caries was diagnosed using criteria proposed by the World Health Organization (WHO)¹⁵ and was quantified using the decayed and filled teeth index (i.e. dft and DFT for the deciduous and permanent dentitions, respectively)¹⁶. The ‘missing’ (i.e. ‘M’) component was not considered in this study population who were in the mixed-dentition stage as its inclusion would result in over-estimation of the caries experience. The caries outcomes used in this study were caries prevalence and caries experience. Caries prevalence is the proportion of the population with at least one decayed tooth in either of the dentitions, while caries experience is the total number of decayed and filled teeth in both dentitions.

A questionnaire was also sent to parents/caregivers, (via their children), to obtain information on parent's occupation, education and family income. With this information, the SES of each family was evaluated using the Kuppuswamy scale, which is a composite instrument that has definite scoring criteria for occupation, education of the head of the household and family income¹⁷. Based on the composite score, the SES of the family was categorised as upper (score: 26–29), upper middle (score: 16–25), lower middle (score: 11–15), upper lower (score: 5–10) and lower (score: <5). As there were very few subjects in the upper (three subjects) and lower (one subject) categories, such subjects were included in the upper middle and upper lower SES categories, respectively. Thus, all children were from one of three SES categories (high, medium or low). In addition, we obtained data on oral hygiene (tooth-cleaning frequency and dental-visiting practices) and dietary practices (frequency of consumption of fruit, sweet food and sugared drinks), which are potential confounders. However, we could not obtain data on the use of fluoridated toothpaste because most of the children were unaware of whether the dentifrice they used contained fluoride.

Ethics approval for this study was obtained from the Griffith University Human Research Ethics Committee, Australia (ref. no.: DOH/12/14/HREC) and the Ethics Committee of Panineeya Institute of Dental Sciences and Research Centre, India (ref. no.: 00126). This research was conducted in full accordance with the World Medical Association Declaration of Helsinki.

Statistical analysis

SPSS (IBM SPSS Statistics for Windows, Version 22.0; IBM Corp., Armonk, NY, USA) was used for statistical analysis. Descriptive data are presented as frequencies and means. The Shapiro–Wilk test of normality was conducted to assess the distribution of the caries data. As these data were not normally distributed, non-parametric tests were used. For bivariate analysis, the Kruskal–Wallis H-test was used to assess differences in dental caries experience between the categories of BMI. The chi-square test was used to determine differences in dental caries prevalence across the categories of BMI. In addition, Mann–Whitney U-tests were also used to evaluate the differences in BAZ, WAZ and HAZ between the caries-severity categories. For the latter, the study population was categorised into high and low caries-severity groups, based on the Significant Caries Index (SiC) and the SiC10¹⁸. In SiC, high caries-severity group constitutes one-third of the total study population with the highest caries experience. The high-caries-severity group, based on SiC10, comprises 10% of the total study population with highest caries experience.

Dental caries experience (dft+DFT) was the outcome variable used in multivariate analysis. A negative binomial regression with a log link was used for multivariate analysis as dental caries experience was widely dispersed. Furthermore, robust estimates were considered in order to avoid the effect of extreme outliers. Explanatory variables were: BMI; gender; SES of the family; frequency of tooth cleaning; dental practitioner-visiting habits; frequency of consumption of sweet foods between meals; frequency of consumption of fresh fruit; and the frequency of consumption of sugared drinks between meals. Furthermore, to evaluate the association between BMI and dental caries across SES categories, separate negative binomial regression analyses were conducted. Exponential estimates of the unadjusted and adjusted regression analysis are presented as incidence rate ratio (IRR). In the adjusted analysis, the effect of all other explanatory variables was controlled. P < 0.05 was considered statistically significant.

Results

A total of 1,284 children were approached and 1,092 participated, giving a response rate of 85%. More than half (58.2%) of the participating children were male. The mean age of the study population was 146.36 ± 11.26 months. Based on the IAP-BMI cut-off values, 13.1% were underweight, while 9.6% were categorised as overweight and 3.7% as obese. There were no significant differences in caries prevalence and experience between the categories of BMI (Table 1). However, overweight children had lower caries prevalence and experience than did the children in other BMI categories. Caries prevalence and experience in overweight children were 24.8% and 0.69 ± 1.51, respectively, and the corresponding figures in normal-weight children were 35% and 0.85 ± 1.50, respectively.

Table 1.

Caries prevalence and experience (dft+DFT) in relation to body mass index (BMI), gender, socio-economic status (SES), oral hygiene and dietary practices

Variable	n (%)	Caries prevalence*	P	Mean (SD)	P
BMI
Underweight	143 (13.1)	30.8	0.183†	0.80 (1.52)	0.272‡
Normal	804 (73.6)	35.0		0.85 (1.50)
Overweight	105 (9.6)	24.8		0.69 (1.51)
Obese	40 (3.7)	32.5		0.93 (1.62)

^*Proportion of the population with at least one decayed tooth in either of the dentitions.

^†Chi-square test.

^‡Kruskal–Wallis H-test.

dft, decayed and filled teeth index for the deciduous dentition; DFT, decayed and filled teeth index for the permanent dentition; SD, standard deviation.

Mean BAZ, WAZ and HAZ values were −0.41 [standard deviation (SD) = −1.09], −0.45 (SD = −1.00) and −0.35 (SD = −1.06), respectively (Table 2). There were no significant differences for BAZ, WAZ and HAZ scores between the categories of dental caries severity. Also, BAZ (high, −0.32 ± 1.18; medium, −0.49 ± 1.08; and low, −0.37 ± 1.01) and BMI (high, 17.34 ± 3.25; medium, 16.91 ± 2.86; and low, 17.30 ± 2.99) scores did not differ significantly between the SES categories (not presented in the tables).

Table 2.

Association between caries severity and anthropometric measures

Caries experience	n (%)	BMI Z score		Weight Z score		Height Z score
		Mean ± SD	Median (IQR)	Mean ± SD	Median (IQR)	Mean ± SD	Median (IQR)
SiC Index*		P = 0.741		P = 0.340		P = 0.385
Low	728 (66.7)	−0.41 ± 1.13	−0.39 (1.48)	−0.43(1.02)	−0.44 (1.00)	−0.33 ± 1.05	−0.45 (1.32)
High	364 (33.3)	−0.42 ± 1.00	−0.43 (1.25)	−0.48 ± 0.96	−0.57 (1.23)	−0.40 ± 1.06	−0.48 (1.36)
SiC10 Index†		P = 0.773		P = 0.707		P = 0.394
Low	958 (87.7)	−0.42 ± 1.10	−0.42 (1.44)	−0.44(1.00)	−0.44 (1.37)	−0.34 ± 1.06	−0.48 (1.35)
High	134 (12.3)	−0.38 ± 1.04	−0.38 (1.32)	−0.47 ± 0.98	−0.45 (1.31)	−0.45 ± 1.06	−0.48 (1.44)
Total	1092	−0.41 ± 1.09	−0.42 (1.41)	−0.45 ± 1.00	−0.44 (1.36)	−0.35 ± 1.06	−0.48 (1.35)

P-values were calculated using the Mann–Whitney U-test.

^*For Significant Caries Index (SiC), high refers to the group which constitutes one-third of the total study population with the highest caries experience and low refers to the rest of the study population.

^†For SiC10, high refers to the group which comprises 10% of the total study population with the highest caries experience and low refers to the rest of the study population.

BMI, body mass index; IQR, interquartile range; SD, standard deviation.

Gender was not related to dental caries experience. Other than SES, none of the explanatory variables was associated with dental caries experience in either bivariate or multivariate analyses (Table 3). Children from high SES families had 41% (IRR = 0.59; 95% CI: 0.44–0.79) fewer caries compared with children from low SES families. The association of SES with dental caries existed even after adjusting for the effect of BMI, gender, oral hygiene and dietary practices (IRR = 0.61; 95% CI: 0.45–0.81).

Table 3.

Multivariate analysis with caries experience (dft+DFT) as the outcome variable and body mass index (BMI), gender, socio-economic status (SES), oral hygiene and dietary practices as explanatory variables

Variable	n (%)	Unadjusted IRR (95% CI)	Adjusted† IRR (95% CI)
BMI
Underweight	143 (13.1)	0.93 (0.67–1.31)	1.00 (0.72–1.40)
Overweight	105 (9.6)	0.80 (0.52–1.25)	0.79 (0.52–1.20)
Obese	40 (3.7)	1.08 (0.62–1.88)	1.13 (0.66–1.96)
Normal	804 (73.6)	1
Gender
Male	635 (58.2)	0.91 (0.73–1.12)	0.86 (0.69–1.08)
Female	457 (41.8)	1
SES of the family
High	289 (26.5)	0.59 (0.44–0.79)*	0.61 (0.45–0.81)*
Medium	517 (47.3)	0.81 (0.63–1.04)	0.81 (0.63–1.04)
Low	286 (26.2)	1
Frequency of teeth cleaning
≤1/day	997 (91.3)	1.13 (0.77–1.64)	1.07 (0.74–1.56)
>1/day	95 (8.7)	1	1
Dental visiting practices
Had been to dentist	227 (20.8)	1.07 (0.83–1.38)	1.18 (0.90–1.53)
Never been to dentist	885 (79.2)	1	1
Frequency of sweet food consumption per day between meals
Sometimes or rarely	928 (8.5)	0.99 (0.72–1.35)	1.02 (0.75–1.40)
Once or more a day	164 (81.5)	1	1
Frequency of fresh fruit consumption per day
Once or more a day	300 (27.5)	0.82 (0.63–1.07)	0.81 (0.62–1.07)
Sometimes or rarely	792 (72.5)	1	1
Frequency of sugared drinks consumption per day between meals
Sometimes or rarely	811 (74.3)	0.85 (0.67–1.08)	0.83 (0.65–1.07)
Once or more a day	281 (25.7)	1	1

^*P < 0.05.

^†Adjusted for other explanatory variables.

95% CI, 95% confidence interval; dft, decayed and filled teeth index for the deciduous dentition; DFT, decayed and filled teeth index for the permanent dentition; IRR, incidence rate ratio.

There were differences in the association of BMI with dental caries across the categories of family SES (Table 4). Among children from families with high SES, overweight children had approximately 71% fewer caries than did normal-weight children, both before (IRR = 0.29; 95% CI: 0.11–0.78) and after (IRR = 0.27; 95% CI: 0.10–0.73) adjusting for the effect of all other explanatory variables. However, there were no differences in caries experience between overweight and normal-weight children from medium (IRR = 1.10; 95% CI: 0.60–2.04) and low (IRR = 0.98; 95% CI: 0.49–1.95) SES families.

Table 4.

Multivariate analysis across the socio-economic status (SES) categories with dental caries experience (dft+DFT) as the outcome variable and body mass index (BMI) as the explanatory variable

SES category	n (%)	Unadjusted IRR (95% CI)	Adjusted† IRR (95% CI)
High SES
Underweight	48 (16.6)	1.34 (0.78–2.30)	1.32 (0.77–2.27)
Overweight	38 (13.1)	0.29 (0.11–0.78)*	0.27 (0.10–0.73)*
Obese	15 (5.2)	1.04 (0.46–2.35)	0.98 (0.45–2.12)
Normal	188 (65.1)	1	1
Total	289
Medium SES
Underweight	65 (12.6)	0.90 (0.53–1.52)	0.85 (0.51–1.40)
Overweight	41 (7.9)	1.10 (0.60–2.04)	1.00 (0.55–1.81)
Obese	15 (2.9)	1.19 (0.52–2.72)	1.20 (0.52–2.78)
Normal	396 (76.6)	1	1
Total	517
Low SES
Underweight	30 (10.5)	0.75 (0.36–1.56)	0.78 (0.38–1.60)
Overweight	26 (9.1)	0.98 (0.49–1.95)	0.96 (0.48–1.92)
Obese	10 (3.5)	1.13 (0.36–3.55)	1.14 (0.39–3.31)
Normal	220 (76.9)	1
Total	286

^*P < 0.05.

^†Adjusted for gender, oral hygiene and dietary practices.

95% CI, 95% confidence interval; dft, decayed and filled teeth index for the deciduous dentition; DFT, decayed and filled teeth index for the permanent dentition; IRR, incidence rate ratio.

Discussion

In addition to evaluating the association between BMI and dental caries, this study also assessed the influence of SES on this association. Subjects were categorised as underweight, normal, overweight and obese using the 2015 growth reference charts proposed by the IAP for Indian children¹⁹. Although WHO growth reference charts for 5- to 19-year-old subjects are commonly used by researchers, they might not be suitable for use in the Indian population as growth patterns in children differ between regions based on the time of puberty and on nutritional, environmental and genetic factors¹⁹.

There was no association between BMI and dental caries: dental caries prevalence and experience did not differ significantly between the categories of BMI. Also, BAZ scores did not differ significantly between the caries-severity categories. In this study, BMI was also used as a continuous variable because categorisation might lead to loss of data, despite being a useful method of presentation²⁰. The literature on the association of dental caries with BMI is conflicting; three systematic reviews9., 11., 21. found no strong evidence of an association, while one reported a small association (i.e. caries in permanent dentition is more prevalent in obese children)⁸. Furthermore, caries assessment methods and BMI classification criteria differed across the studies included in these reviews.

Similarly to the above, there have been conflicting findings from studies in adolescent and child populations in India. Half of these studies observed no association22., 23., 24., 25., 26., while the other half found a direct association, with more caries being reported in children who were obese or overweight27., 28., 29., 30., 31.. An important reason for the discrepancies, that also influences any comparison between the studies is non-uniform BMI cut-off values. For example, one of these Indian studies used the International Obesity Taskforce standards²⁹ and another used the Centre for Disease Control 2000 growth charts³⁰. Only one study²⁸ used growth standards specific to Indian children, namely the IAP 2007 growth references. Although IAP 2007 growth-chart guidelines are specific to Indian children, they were formulated based on the data from a multicentric study conducted almost three decades ago, in 1989¹⁹.

Although not statistically significant, caries prevalence and experience was lower in overweight children than in children from other BMI categories. Similar observation was made in a few longitudinal10., 32., 33. and cross-sectional studies on national representative samples34., 35.. Although the underlying reason for this inverse association is unclear, several studies have attributed it to dietary habits. One of these studies suggested that although parents of overweight children may restrict the consumption of sugary food, thus leading to development of fewer caries, the children remain overweight because they consume more calories than they expend³³. Another study reasoned that overweight children might consume more fatty acids, but less sugar, compared with healthy or underweight children³².

Children of low SES were at greater risk for dental caries compared with children of medium and high SES. It is explicitly evident from the systematic reviews that lower SES is associated with greater caries experience, both in adults and in children36., 37.. For SES categorisation, the composite scale of Kuppuswamy has been used rather than SES scales based solely on family income. Although income plays an important role in meeting the immediate needs of the family, it is not an appropriate measure of social class³⁸.

It was observed that frequency of consumption of sweet foods, fresh fruits and sugared drinks was not associated with dental caries. In this study, two closed-ended questions were used to assess sugar-consumption frequency, which might have obscured the association of dietary sugar and dental caries. Furthermore, this association is mediated by several factors, such as salivary flow rate and composition, fluoride usage, the posteruptive age of the teeth³⁹ and the consistency⁴⁰ and amount of sugar⁴¹, which were not recorded in this study.

When subgroup analysis on the association of BMI and dental caries across the SES categories was performed, overweight children had fewer caries than did those with normal BMI. This finding is consistent with results from a longitudinal study in Scandinavia, in which lower caries experience predicted a larger increase in body weight over a period of 6 years only in children of mothers with more than 10 years of education¹⁰. In the case of our Indian families, children of parents with higher SES may tend to follow better preventive oral hygiene practices42., 43. but remain overweight because of over-feeding by their parents. An overweight child is traditionally considered as being of normal weight⁴⁴ and healthy by Indian parents⁴⁵. This misperception about children's weight exists in parents from diverse ethnic backgrounds46., 47.; some studies observed that South Asian parents have increased likelihood of misclassifying their overweight children as being of normal weight⁴⁸.

This study is the first to explore the effect of SES on the association of BMI with dental caries in an Indian population. The study findings have good external validity as the non-response bias was minimal (the response rate was 85%). The main findings of the study, namely lower caries prevalence and experience in overweight children and the influence of SES on this relationship, are in contrast to the literature on the intake of free sugar, dental caries, and nutritional status. This warrants longitudinal and life-course studies on larger representative populations from diverse cultural backgrounds to understand the interplay between social disparities, BMI and the severity of dental caries. In order to facilitate international comparisons, it would be beneficial if future studies were to use uniform and appropriate methods for assessing caries, SES, and BMI. Dentists from the study region, in their position as health-care providers, can educate and motivate parents, particularly those children who are overweight, on healthy eating practices. Furthermore, health-education programmes for preventing dental caries and obesity, with multisectoral co-ordination between health and education departments of the state, should be contemplated. Data obtained from this study can act as baseline information and can be helpful in evaluating the effectiveness of the implemented programs.

Limitations

The findings of this study cannot be generalised to the Indian population as a whole because the sample was recruited from sixth-grade children of selected schools only. However, our subjects were representative of school-going children of the Medak district in India and typical of rural/semi-urban children across the whole of south India. The data obtained on SES were self-reported. Furthermore, nutritional status and dental caries experience are multifactorial, and their relationship is likely to be weakened by confounding variables, notably fluoride usage, which was not assessed in this study.

Conclusions

Overall, BMI was not strongly associated with dental caries in this population. Although not statistically significant, caries prevalence and experience were lower in overweight children. The association of BMI with dental caries varied across SES categories. Overweight children of high SES were at less risk of experiencing dental caries compared with normal-weight children, while this association was not observed in children of low and middle SES.

Acknowledgements

We would like to acknowledge the support of Griffith University and Panineeya Institute of Dental Sciences and Research Centre in conducting this study. We also thank the district education authorities of Medak district and the study participants for their co-operation. This study did not receive financial support from any organization.

Competing interest

The authors declare that they do not have any competing interests.