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Revista Brasileira de Epidemiologia

Print version ISSN 1415-790XOn-line version ISSN 1980-5497

Rev. bras. epidemiol. vol.19 no.1 São Paulo Jan./Mar. 2016

http://dx.doi.org/10.1590/1980-5497201600010013 

Original Articles

Dietary intake of antioxidant in ELSA-Brasil population: baseline results

Marina Galvão TeixeiraI 

José Geraldo MillI 

Alexandre Costa PereiraII 

Maria del Carmen Bisi MolinaI 

IUniversidade Federal do Espírito Santo - Vitória (ES), Brazil.

IIUniversidade de São Paulo - São Paulo (SP), Brazil.

ABSTRACT:

Objective:

To quantify the antioxidant consumption (vitamins A, C and E and minerals selenium and zinc) and to identify factors associated to low consumption of these nutrients.

Methods:

Cross-sectional study with 14,660 participants (35 to 74 years-old) investigated in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) baseline. Consumption of antioxidants and energy was determined by a Food Frequency Questionnaire and analyzed using the NDSR software. Antioxidant consumption was adjusted to total energy and divided in quintiles. A logistic regression analysis was used to identify socioeconomic factors associated with low intake of these nutrients.

Results:

Consumption of energy (kcal/day) was higher in men (3,152 ± 1,026 versus 2,613 ± 905; p < 0.001) whereas the consumption of all antioxidants (mainly vitamins A and E and selenium) was higher in females. Low antioxidant consumption was associated to male sex (OR = 3.5; 95%CI 3.11 - 4.0) and to lower education (OR = 3.1; 95%CI 2.42 - 3.87), income (OR = 4.4; 95%CI 3.67 - 5.36) and age (OR = 5.5; 95%CI 4.27 - 7.16), as well as to thinness (OR = 2.7; 95%CI 1.36 - 5.18) and when participants did not reported the use of supplements (OR = 1.95; 95%CI 1.6 - 2.38) or change of eating habits in the last six months (OR = 2.0; 95%CI 1.75 - 2.29).

Conclusion:

The greater intake of fruits and vegetables is likely to be involved in the higher consumption of antioxidants in females. General policies to increase the consumption of such nutrients should be directed to groups of lower income, education and age.

Keywords: Antioxidants; Nutrients; Food consumption; Socioeconomic factors; Longitudinal studies; Logistic models.

INTRODUCTION

Free radicals are produced continuously in the body, being kept within the normal limits by inactivation and removal procedures. Imbalance in these procedures may be generated either by an increase in production and by insufficient removal. An imbalance in the prooxidant/antioxidant balance results in the increase of oxidative stress, in which the excess of oxygen reactive species may determine cell damage1. In turn, the increased oxidative stress is related to the development and worsening of many chronic diseases, such as diabetes, cardiovascular diseases, obesity, and cancer2, which have great impact in the current standard of Brazilian morbidity and mortality3.

The dietary intake of antioxidant nutrients, specially through the consumption of fruit and vegetable, may reduce the oxidative stress, once they are able to eliminate free radicals in a direct way, as is the case of vitamins, or in an indirect way, through minerals, which acts as cofactors of antioxidant enzymes4,5.

A diet rich in fruit and vegetable and, consequently, in antioxidant nutrients is recommended as a part of a healthy diet; however, more than 90% of the Brazilian population has lower consumption of daily servings than the recommended one for those foods. Besides, the frequency of intake of fruit and vegetable is positively associated with income, and school education positively influences the percentage of individuals who reach the recommended intake of these foods6.

The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) has the objective of identifying the determinants of incidence of chronic disease in the Brazilian population, focusing mainly on diabetes and cardiovascular diseases7. Considering that the dietary pattern has a strong influence on the development of many chronic diseases8,9 and that the oxidative stress seems to mediate part of this influence, our objective was to quantify the intake of antioxidant nutrients (vitamins A, E, and C and the minerals selenium and zinc) and to identify the factors associated with this intake in the baseline of ELSA-Brasil.

METHODS

It is a data analysis of participants included in the baseline of ELSA-Brasil, in the period from 2008 to 2010. The cohort consisted of 15,105 adults of both genders and aged between 35 and 74 years, all active workers or retired persons from 6 higher education and research institutions located in 6 Brazilian states (Rio Grande do Sul, São Paulo, Rio de Janeiro, Minas Gerais, Espírito Santo, and Bahia). The overall data collection and the general description of the cohort were published previously7,10. The data regarding school education, income, use of supplements, and change of dietary habits within the last 12 months were obtained in an interview. The per capita income was estimated by the information of the approximate net family income in the month before the interview and the number of people who depend on it. Weight and height were measures during clinical tests7, and the nutritional status of the patient was determined by the body mass index (BMI; kg/m2) and classified according to the recommendations by the World Health Organization11. The categories of overweight and obesity (excess of weight) were grouped together.

The usual dietary intake of participants was obtained by the Food Frequency Questionnaire (FFQ) developed and validated for this purpose12,13. The FFQ ELSA-Brasil is a semiquantitative questionnaire consisting of 114 items, whose objective is to evaluate the usual intake within the last 12 months. The daily intake of nutrients and calories was estimated with the help of the Nutrition Data System for Research (NDSR) software. The extreme values of consumption (over 99%) were substituted by the exact value of 99%. In addition to that, when the participant, voluntarily, reported the seasonal consumption of any item/food or drink, the total value of daily consumption of this food was multiplied by 0.25.

This study excluded individuals who did not have all dietary data or who did not reveal plausible daily caloric intake (< 500 or > 6,000 kcal)14. The daily intake of antioxidant nutrients was adjusted by energy according to the method proposed by Willett15 and categorized into quintiles. A variable representing the total antioxidant consumption was also created, given by the sum of intake quintiles of five nutrients (Total antioxidant intake = Quintile Vit A + Quintile Vit C + Quintile Vit E + Quintile Zn + Quintile Se). Thus, this variable took over values between 5 and 25, also being analyzed according to the distribution of quintiles.

The statistical analysis was performed by the SPSS 19.0 software. The Kolmogorov-Smirnov test was used to verify the normality of the quantitative variables. Parametric or nonparametric bicaudal tests were applied when necessary. The significance level was established for p < 0.05. The χ2 test was used to compare the categorical variables. The nonparametric Mann-Whitney test was used to compare the two means and the ANOVA of Kruskal-Wallis in the comparison of means of three or more groups. The logistic regression was used to test the hypothesis of association between the consumption of antioxidants and the socioeconomic variables and BMI.

The ELSA-Brasil was approved by the Research Ethics Committee of each institution where the project is being carried out. All participants signed the informed consent before data collection.

RESULTS

The analysis excluded 445 participants (2.9% of the sample) owing to the absence of complete data. Table 1 shows the sociodemographic and BMI variables, according to gender. The sample consisted of 44.8% of men and 55.2% of women (mean age = 52 ± 9 years). As for race/color, 53% subjects were self-reported as Caucasian/white; 8.1% of participants were retired at the moment of the collection (data not presented in the table). Regarding school education, 12.3% were educated up to full elementary school education, 34.1% up to complete high school education, and 53.6% up to full high education. The mean per capita income was R$ 1,768 ± 1,448. In the studied sample, the male gender showed higher percentage in the category of lower school education, lower percentage among the eutrophics, as those who reported use of supplements, and among those who reported changes in their eating habits.

Table 1: Distribution of the sample according to the socioeconomic and health variables according to gender (ELSA-Brasil, 2008 - 2010). 

*Regarding the χ2 test; **reporting of change of eating habits within the last 6 months. The total values of the groups may vary owing to missing data.

About 31% of the studied population reported changes in their eating habits; of those, 61% were women, approximately 72% of them were overweight, and 55% of them were educated up to full college degree. The change of habits was related to the per capita income (p = 0.029) (data not presented in the table).

Even though the data of nutrient intake used in this study refer only to dietary intake, it is important to highlight that there was a reference on the use of multivitamins or minerals, which may interfere in the available organic quantity of nutrients. The regular use was reported by 13.1% and the nonregular use by 9.7% of the sample, totaling 3,302 participants (22.5% of the sample).

The mean daily caloric intake of the sample was 2,855 ± 998 kcal, with significant difference between the genders. When compared with the energetic consumption of antioxidant nutrients between men and women, a higher energy intake and lower means of antioxidant intake among men (Table 2) were observed. The intake of all antioxidants was higher among women than among men, with the largest differences observed for vitamins A and C, 18 and 25% and more among women, respectively.

Table 2: Mean and standard deviation of energy and antioxidant nutrients adjusted by energy, according to gender (ELSA-Brasil, 2008 - 2010). 

*Mann-Whitney test; SD: standard deviation.

Tab le 3 presents the sociodemographic characteristics and BMI according to the consumption quintiles of each of the antioxidants. The variables presenting direct relation to it were: age, income, high education, and use of supplements, and the variables which presented indirect relation to it was the percentage of men. This result was similar for the total intake of antioxidants (Table 4). For vitamins A, C, and E and zinc, a significant association with school education was observed (Tab le 3). However, this trend was continuous up until the fourth quintile, becoming inconsistent when comparing with the penultimate and lat quintiles for each one of the oxidants. In relation to age, the percentage variation was not growing when comparing each quintile with the previous one in the case of selenium, and there was no influence in relation to zinc intake.

Table 3: Quintiles of intake of antioxidant nutrients, adjusted by energy, according to socioeconomic and health variables of the participants in ELSA-Brasil (ELSA-Brasil, 2008 - 2010). 

Table 3: Continuation. 

*Kruskal-Wallis and χ2 test; **regarding the category: college + graduate degree. The continuous values are related to the means in the quintiles.

Table 4: Socioeconomic and health variables according to the quintiles of intake of antioxidant nutrients (ELSA-Brasil, 2008 - 2010). 

*Regarding the Kruskal-Wallis and χ2 tests; **regarding the category: college + graduate degrees. The continuous values are related to the means and standard deviations of the quintiles.

Table 4 shows the socioeconomic and health variables according to the quintiles of the variable "total intake of antioxidants." A clear increased intake according to age, income, education, use of supplements, and the reporting of changed eating habits was observed. The participation of men decreases with the increasing consumption quintile. Table 5 shows the results of the logistic regressions, in which the fifth quintile of antioxidant intake was the reference category, and the results presented are for the first quintile (low intake). Men have 3.5 times more chances of belonging to the lowest antioxidant intake category, similar to individuals with low education (3.1 times) and to those classified in the first income tertile (4.4 times). The low antioxidant intake was also associated with the youngest age ranges and low weight. Those who did not report using supplements or having changed their eating habits also revealed higher chances of belonging to the group with the lowest antioxidant intake.

Table 5: Odds ratio and confidence interval of factors associated with low intake of antioxidants (ELSA-Brasil, 2008 - 2010). 

*Reference category: fit quintile (high intake of antioxidants).

DISCUSSION

The consumption of antioxidant nutrients was higher among women, among individuals of higher age range, and among those with higher education and income. In addition to that, there was a positive relation with the use of supplements and with changes in the eating habits.

Xun et al.16 found a positive relation between education and the concentrations of selenium in the fingernails of African Americans; a similar result was found in this study regarding selenium intake, for a mixed/multiracial population. In relation to the consumption of zinc, the ELSA-Brasil population showed a mean above the one verified by Sun et al.17 in a longitudinal study (data from the Nurse's Health Study). There, the first quintile revealed mean dietary intake of zinc of 2.7 mg/day and the fifth quintile of 10.7 mg/day, while in this study, the means of the first and the fifth quintile were 12 and 22 mg/day, respectively.

In a study investigating the intake of antioxidants in the American population18, researchers found means of daily dietary intake of vitamins C and E and selenium lower compared with those found in this study. In the same study, the nutritional state (BMI) showed a direct relation to the consumption of selenium and an inverse relation to the dietary intake of vitamins C and E. In this study, the BMI category "underweight" showed an inverse association with the total consumption of antioxidants; however, the "excess weight" (overweight and obesity) showed a positive association with the total consumption of antioxidants. Similar to the findings in the ELSA-Brasil cohort, the highest intake of antioxidants from diet belonged to the highest age range and income.

The difference found between the Brazilian and the American studies may be related to the dietary composition of the cultures investigated, as the instrument used in the studies was the same (QFA), although each of them adapted to the eating habits of each group. Besides, the characteristics of the populations chosen in each study may justify these differences, including age range, education, and income, because that, as shown in these works, these characteristics are associated with a broad variation of antioxidant intake. ELSA-Brasil reveals a wide age range, beginning with adults from 35 years of age and onward; on the other hand, in the study by Chun et al.18, the lowest age was 19 years.

An association between low antioxidant intake and the BMI categories (underweight and excess weight) occurred, possibly, owing to the characteristic association of caloric consumption of these groups. The positive relation of the use of supplements and the reports of changed eating habits with the consumption of antioxidants may reflect in behavior of greater health care.

Some studies investigating the intake of fruit and vegetable, the main sources of antioxidants, identified a direct association of the intake of these food groups with education, by the isolated variable19, or by the composite variables, such as socioeconomic status20 and the relation of intake of these food with income21 and age22. Wyndels et al.23 found in a sample of French population a direct relation of the income tax rate with the joining to the national nutrition program of the country, regardless of geographical factors.

In a literature review on the socioeconomic status (which considered education, income, and occupation) and the intake and/or nutritional status of micronutrients in the European population, it was found that the lowest intake values were in the category of low socioeconomic levels. Education presented greater effect in the relation of socioeconomic status and intake, which may be owing to the education level determining income and occupation and, moreover, it may interfere in the understanding and carrying out of eating behaviors to reduce risk24.

The design used in this study showed limitation characteristics of cross-sectional studies, owing to nontemporal monitoring of the individuals, limiting the control of the behavioral variables25. The use of the instrument for dietary data collection (QFA) also revealed limitations, as the collection included what the researcher wished to cover for the measuring and the time of collection, up to the conversion into "nutrient intake" per gram, may overestimate the individual consumption26,27.

However, some procedures were carried out in order to minimize the possible mistakes in answers: there were previous and periodic trainings of the interviewers for the correct approach; during the interview, a kit of tools in order to facilitate the identification of portion sizes was used; a response card with the options on frequency of intake was handed to the patients in order to facilitate choice, without need for memorization.

In this study, the low intake of antioxidants was associated with the following conditions: male gender, low education, higher income, younger age ranges, underweight BMI, absence of use of supplement, or change in eating habits within the last 6 months. It may be concluded that the actions of nutritional education focused on the increase of food rich in antioxidant nutrients intake must be directed specifically to the groups with the specific characteristics of low antioxidant intake.

CONCLUSION

The total antioxidant intake was positively associated with the female gender, higher age range, income, and education, a higher prevalence of excess of weight, use of supplements, and change in eating habits within the last 6 months.

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Financial support: Ministry of Health (Decit - Science and Techonology Department) and Ministry of Science and Techonology (Finep - Financier of Studies and Projects and CNPq - National Council for Scientific and Techonological Development, Processes Nos. 01 06 0010.00 RS, 01 06 0212.00 BA, 01 06 0300.00 ES, 01 06 0278.00 MG, 01 06 0115.00 SP, 01 06 0071.00 RJ).

Received: January 08, 2015; Accepted: September 15, 2015

Corresponding author: Maria del Carmen Bisi Molina. Avenida Marechal Campos, 1468, Maruípe, CEP: 29040-090, Vitória, ES, Brasil. E-mail: mdmolina@uol.com.br

Conflict of interests: nothing to declare

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