The HBSC study is the primary source of data to measure trends in children's health behaviours, including changes in food consumption over time in Lithuania. The data are collected from countrywide representative samples, with questionnaires repeated at regular four-year intervals. Using consistent methodology for subsequent studies, measures are taken to ensure the population is evaluated, and the methods used for dietary surveys, social and economic measures, data processing and analysis are all consistent with prior surveys. The methodology used in this study corresponds with international standards and international comparison, including analysis of dietary intake trend data from varying countries [13
The HBSC study report [9
] assembles a comprehensive cross-national picture of the eating habits of young people from 41 countries and regions. According to their nutrition habits, Lithuanian schoolchildren take various positions on the rating scale, when compared with their peers from other countries and regions. Lithuanian children eat fruits and vegetables relatively rarely. Data from 2002, 2006 and 2010 surveys indicate that only 21.1% boys and 27.1% girls had daily intake of fruits; on average, 24.9% of boys and 29.6% of girls reported daily intake of vegetables. For all surveys, national data were significantly lower than the average rates in HBSC countries (in 2005-2006, only 15-year-olds from Greenland reported less consumption of fruits than Lithuanians [9
]). Our data on fruit and vegetable consumption were similar to the data from other studies carried out in Lithuania [17
]. Thus, with regards to fruit and vegetable consumption we conclude that Lithuanian school-aged children consume these products less often. Surely, there could be seasonal explanations as these studies were completed in springtime, when accessibility of fruits and vegetables is reduced in our country, but this limitation was common for all mentioned studies.
In regard to consumption of less healthy food products (sweets and chocolates, biscuits and pastries, soft drinks, chips and fast food), in this cross-national perspective Lithuanian school-aged children should becharacterized positively. The data from the HBSC survey showed very large variations in soft drink consumption between countries. Lithuanian children had one of the lowest reported levels of soft drink consumption [9
]. Compared to the EU average, Lithuanian children rarely consumed sweets and soft drinks (Coca-Cola, Sprite or other) on a daily basis in 2001-2002 [19
It was found that girls of all ages eat fruits, vegetables, sweets or chocolates more often than boys; however, an inverse gender difference exists for consumption of soft drinks, chips and fast food. Daily fruit and vegetable consumption drops significantly between the ages of 11 and 15 years among Lithuanian children. These gender and age specific differences are the case among school-aged children in the majority of HBSC countries [3
] and have also been observed in other studies [11
]. These studies demonstrated that older school-aged children tend to consume less fruits and vegetables than younger school children due to growing peer influence and reduced impact of parents [11
Given the current need to explain the reasons for the healthy and unhealthy food consumption, social determinants should be explored as the main factors that might influence nutrition among school-aged children. The effect of these determinants can be different for different food items [21
In our study only four social position variables (place of residence, family structure, SES and subjective rating wealth), which were measured by the same methods in all surveys, were included in the analysis. Subjective rating of family wealth, which is a summarizing measure, was used for more detailed analysis and comparison of different social groups of adolescents.
Upon comparing respondents by place of residence, greater daily consumption of fruits was found among both boys and girls living in rural areas, while a more prevalent consumption of vegetables was found among only rural boys. Regular consumption of sweets and chocolates was about 1.5 times more likely among children from rural areas, whereas their peers from urban areas were 1.5 times more likely to eat biscuits and pastries, and to drink soft drinks. On the one hand, such associations might be explained by the difference in the availability of these foods between urban and rural children. Studies in USA, for example, revealed living closer to convenience stores (supermarkets) was associated with increased consumption of crisps, chocolate and white bread [24
]. Urban corner shops can be a major risk for children's nutrition because the most frequently purchased items low-nutritive foods and beverages that are energy dense, such as chips, candies and sugar-sweetened beverages [25
]. On the other hand, considering the data from Statistics of Lithuania the average disposable income per household per month in urban areas is much higher than in rural areas, although converse consumption expenditure for food is fixed in our country [26
]. Consequently, economic differences by place of residence are sharp in Lithuania and can provide one explanation for nutrition inequalities among school-aged children.
Fruit and vegetable consumption increased with family social-economic status and family material wealth (children living in high socioeconomic/rich families were 2 times more likely to eat fruit and vegetables daily than children living in low socioeconomic/poor families). In addition to fruits and vegetables, significant differences between SES groups in sweet and chocolate consumption were also found in our survey. This finding could probably be explained by higher prices of these food products in Lithuania. There is considerable evidence for correlations between low household food budgets and the consumption of cheaper, low-nutritive foodstuffs [11
]. Studies confirm that school-children reporting food poverty are less likely to eat fruits, vegetables and brown breads, (odds ratios (ORs) varied from 0.66 to 0.81), and are more likely to eat crisps, fried potatoes and hamburgers (OR varied from 1.20 to 1.62) [27
]. Lower fruit and vegetable prices, higher fast food prices, and greater supermarket availability are related to higher fruit and vegetable consumption, especially among teenagers who are at risk for overweight and who are low-to middle-socioeconomic status [28
According to our data, family structure was a significant predictor of nutrition inequalities among Lithuanian adolescents; however, only in cases of reduced chip intake and increased vegetable consumption in girls, who live in intact, as opposed to non-intact, families. Our analysis demonstrated that non-intact families have decreased overall nutrition, due to lower income and home comfort [30
]. Previous studies reinforce our results, suggesting significant differences exist between "healthy" and "unhealthy" food consumption among children living in intact and non-intact families, which are mainly related to divorce [5
]. Psychological factors after divorce also have a large influence on a child's nutrition and health [33
In Lithuania, social factors included in the present analysis, changed significantly during the study period. It is possible these social factors affected the eating habits and health of young people. We recorded more children living in urban areas as well as those living in non-intact families, although positive changes in SES and subjective rating of family wealth were identified. Meanwhile, many macro-social rates changed in our country and most of them turned negatively [9
]. The rates of unemployment increased [34
] as well as the risk of poverty for families with children [35
]; food prices (especially in fruits and vegetables, dairy products and grain) raised in Lithuania over past years [36
]. Changes in social environment may have had an impact on the dietary intake of Lithuanians, particularly among children. Monitoring time trends of dietary habits and social determinants is very important for testing such a hypothesis. In a large measure, our study offers such opportunity, as three regular cross-sectional surveys on a representative sample of population were carried out by the same methods of data collection between 2002 and 2010.
Most studies on social inequalities in habitual dietary patterns are based on cross-sectional data collection design [21
], or under presumption that the differences between SES classes were rather stable over time [38
]. In this regard, identification of associations in time trends analysis is a difficult task in social epidemiology. However, in the present study, we hypothesized that associations between eating behaviour of children and the survey year were explainable by a differential distribution of social variables across survey years. Adjustment of data across years of the survey, by including social variables into the model, provided empirical evidence for the impact of social inequality changes. Similar approaches have been used in other studies, irrespective of the scientific problem addressed [40
The method of data adjustment for social determinants revealed that the trends of fruit and vegetable consumption, among Lithuanian schoolchildren, were associated with changes in social inequalities over the past decade. The highest decrease in time trends of odds was observed for daily eating of fruits (among boys in 22.5% and among girls in 34.0%, comparing 2010 to 2002). Thus, our findings provide consistent evidence for nutritional inequalities in Lithuanian school-aged children, showing a lower consumption of fruits and vegetable due to socio-economic disadvantages [27
]. Therefore, nutrition changes need to be assessed in consideration with future social and economic changes.
Evidence suggests that school fruit and vegetable programmes can increase fruit and vegetable consumption among children by as much as 70 percent [4
]. These schemes have the added benefit of improving dietary intake of children from low socio-economical backgrounds and reducing health and social inequalities [4
]. Decline in the consumption of unhealthy foods was observed in 2010 for both sexes. These trends could be explained by the implementation of several health policies and interventions, such as fruit and milk promotional programmes in secondary schools, in Lithuania [44
]. In regard to these findings, fruit and vegetable programmes should be high on the political agendas in Lithuania and other countries. Healthy nutrition strategy should be put in practice, since positive changes in child nutrition are expected only when health inequalities in Lithuania are minimized.
The study provides national information about eating behavior and trends among school-aged children in changing social environment. The HBSC questionnaire, which was approved through a series of validation studies, was used for data collection. Despite concerted efforts to obtain reliable data sets for all repeated cross-sectional surveys, data gathered by self-reported food frequency questioning and social assessment remain a matter of great concern. A possible information bias may have been introduced by small changes in item formulations and response categories between surveys [3
]. Also, changes in the wording, number and order of response categories influence the participants' responses [45
]. In order to avoid any bias related to these changes, data on food consumption from only three surveys in 2002, 2006 and 2010 were used in the present study. For similar reasons, only four social variables were selected to describe the individual social environment of respondents.
The questions on nutrition were designed to provide information on the frequency of food items consumption, but not the quantities consumed. The literature shows varying results regarding the validity of self-reported dietary assessment methods among adolescents [46
]. However, a validation study of the food frequency scale, which was used in the present study to assess respondents' eating behavior, showed high test-retest reliability and acceptable validity compared to 24 hour food behaviour checklists and a 7-day food diaries [47
]. While it is considered that data generated by food frequency scale may be less suitable for estimating prevalence levels, its applicable for trend analyses is prevalent [3
One of the major difficulties in monitoring health inequalities among children is the choice of relevant measures for socio-economic status of respondents [48
]. Unfortunately, measuring the social environment of respondents in our study was limited to four items, due to previously mentioned reasons. These items can act as determinants in the relationship between household wealth and child's food consumption, but relationships and interactions between these items were not considered. Multivariate analysis would be needed to gain more insight into these relationships, and thus into the underlying mechanisms linking wealth and food consumption among children. Further explorations of possible causes (for example prices, marketing polices, etc) of the observed changes in food intake require a broader approach than is possible in the context of this paper.
Finally, when examining social inequalities, a problem of artifact changes in rates arises if the sizes of the social groups differ between surveys. To reduce such difficulties in measuring health inequalities some authors [48
] recommend applying the Relative Index of Inequality, which is an overall measure of the magnitude of inequality across all wealth groups. In the present study, we attempt to solve this problem in part by adjusting data in logistic regression models.