This study examined the pattern of intake of sweet drinks, including nutritively sweetened soft drinks and fruit juice/cordial, among children and adolescents from Victoria, Australia. According to the dietary recalls more than 70% of the children and adolescents consumed sweet drinks and of these consumers, 40% had the equivalent of more than two cans (≥750 ml) of sweet drinks. Significantly more participants consumed fruit juice/cordial compared to soft drinks. The proportion of participants who reported consuming sweet drinks overall, and fruit juice/cordial specifically, varied with gender but remained stable across age groups, however there was a greater proportion of soft drink consumers in the older age groups. The proportion of children and adolescents consuming sweet drinks remained relatively stable over time, with some significant decreases in consumption, both longitudinally within cohorts, and in repeated cross-sections of comparable age groups.
Intake of sweet drinks
The majority of existing research on sweet drink consumption has focused specifically on soft drinks. This study found that almost one third of the children and adolescents consumed soft drink -on the previous weekday. That is substantially higher than has been reported in other Australian studies. One study, from another Australian state (Queensland) found that between 11 and 19% of females and 12 to 28% of males had consumed soft drinks on the previous day, with a marked increase with age . In contrast to the current study the Queensland sample did not include adolescents from age 16–18 years, where we found a high proportion of consumers. A more recent study, based on the 2007 Australian National Children’s Nutrition and Physical Activity Survey (NCNPAS), reported proportions of sweet drink consumers more similar to ours, in the range 19 and 38% among males and 17 and 29% among females for children aged 4–16 years . The proportion of consumers of soft drink in the present study is; however, considerably lower than in other countries with comparable data. A 2004–05 study in Texas found that (depending on age) between 50 and 60% of children and adolescents aged 9–17 years consumed soft drink the previous day  and a Mexican study from 2006 reported that 76% of participants (5–11 years) consumed soft drink on a daily basis . While there are methodological differences between these studies it seems likely that there are substantial differences in consumption of soft drink both between populations within Australia and between Australia and other countries. In addition, the prevalence of children and adolescents consuming any type of sweet drink (including both soft drink, sugar-sweetened beverages and fruit juice) is substantially higher in the United States (US) than was observed in the present study, according to analysis by Wang and colleagues based on the National Health and Nutrition Examination Surveys (NHANES) 1999–2004 . They found that 90% of the participants (2–19 years) consumed any type of sweet drink the previous day  compared to 77% in the present study at time 1 and 71% at time 2.
In the present study more children and adolescents consumed fruit juice/cordial than soft drink, which is consistent with results from studies in the state of New South Wales [2, 3]. In Texas, the proportion of children and adolescents consuming fruit juice, fruit-flavoured drinks and soft drinks was similar across all three categories of beverages (47-62%) . The study based on the Australian NCNPAS reported that overall 37% of children and adolescents consumed fruit juice, 25% consumed soft drink and 20% consumed cordial on the previous day .
In the present study more participants in the older age groups consumed soft drinks. A similar trend has been observed in Queensland , nationally in the NCNPAS [21, 22] and in the US . In the present study there were no differences between the age groups in the proportion of children drinking fruit juice/cordial. It was observed that among the adolescents more males than females consumed any sweet drinks and also the volume of sweet drinks consumed was higher among males, consistent with previous findings from Australia [20–22], Mexico  and Texas, US .
Longitudinal changes over time
In the cross-sectional analysis there was a higher proportion of consumers of soft drink in the older age groups. It was therefore expected that the proportion of consumers would increase with age (over time) in the longitudinal analysis. However, in the longitudinal analysis there was a non-significant trend towards a lower percentage of children and adolescents drinking any type of sweet drinks and fruit juice/cordial and soft drinks separately after approximately two year follow-up, although this was only significant for some age groups.
Cross-sectional changes over time
In the analysis of secular changes in consumption from time 1 to time 2 a similar non-significant trend was seen. These findings indicate a stable or even decreasing percentage of Victorian children drinking any type of sweet drink. Even though no intervention was made in the comparison groups the inclusion of the children and adolescents in the studies may have lead to greater awareness on healthy eating in general and decreased intake of sweet drinks and/ or decreased reported intake of sweet drinks. Furthermore, in BAEW the data at time 1 were collected over a long time period including summer/autumn while data at time 2 were collected in winter/spring, which may have affected the results as well. A recent study from Queensland, however, reported similar results as found in the present study for soft drink and concluded that there was a reduction of soft drink consumption in 2008 compared to 2003 . Preliminary analysis from NHANES in the US (2003–04 and 2005–06) also indicate a decrease in the average intake of soft drink and fruit juice among US children . The Australian Beverage Industry has reported a decrease in sales of sugar-sweetened carbonated soft drinks and an increase in sales of non-sugar-sweetened carbonated soft drink and water between 1997 and 2006, and especially from 2002  which supports the observed trends in the present data.
The results from the present study also indicate a lower volume of soft drink intake at time 2 among the children (4–12 years) compared to time 1, however, the question assessing soft drink intake in BAEW was slightly altered from time 1 to time 2 and this may have had some effect on the apparent changes in intake of soft drink in most of the age groups from BAEW. Based on the data presented by the Australian Beverage Industry reporting an increase in the sale of diet beverages and water among the adult population  it is possible that some children and adolescents also have changed the intake of regular (sugar-sweetened) soft drink to diet soft drink or packaged water. In addition, there were substantial changes over the study period in the regulation and operation of school canteen services in Victoria, which may have impacted on the availability of sweet drinks on school days [39, 40].
The strengths of the study include the collection of data on both one day’s intake (yesterday/ last school day) and intake last week or month. The correlation between the two measurements is moderate to high , which supports the use of the single day recall questions that are generally simpler for participants to answer. The longitudinal design provides the opportunity to study changes in beverage intake within the same group of children over time and the combination of two closely related studies enabled assessment of beverage consumption patterns across childhood and adolescence in a large sample. The two studies had very similar designs, and methodological differences between them were relatively minor. One exception to this was the dietary data being self-reported by adolescents (IYM) and parent-reported for primary school children (BAEW); however, given the ages of the participants, these methods are most appropriate for obtaining accurate recall data. Furthermore, the use of comparison groups meant that only the background health promotion activities were operating in the populations.
The limitations of the study include that the analyses were based on single 24-hour reported beverage consumption, either yesterday’s intake or intake on the last school day, which may not reflect long term intake due to day-to-day variation in food and beverage consumption. Furthermore, the use of one day’s intake as an indicator of sweet drink consumption may increase the risk of misclassification and thereby the probability of type II errors. Moreover, the reported beverage intake is potentially subject to the limitations inherent in most dietary assessment methods including recall bias , underreporting  and social desirability bias , which may be especially pronounced for snack and sugar intakes . Additionally, parents may not be fully aware of what their child drinks during the day, especially when the child is away from home . In both studies only intakes of selected foods and beverages were assessed which imposes a substantially lower burden on the respondents  and may result in higher participation rates, among the adolescents compared to a 24-hour recall; however it precludes analyses that consider total energy or other nutrient intakes.
Due to the geographic limitation of the study, the results may not be generalizable to all Australian children and adolescents. Also the large number of participants lost to follow-up and the over representation of families residing in low SES areas restrict the generalisability of the results of the study. Generally, children and adolescents lost to follow-up between time 1 and time 2 had a higher intake of both soft drink and fruit juice/cordial (BAEW: soft drink p = 0.004, fruit juice/cordial p = 0.03, IYM: soft drink p < 0.0001, fruit juice/cordial p = 0.08) than those participating at both time points. No difference was observed in BMI between children who participated at both time 1 and time 2 and children who were lost to follow-up after time 1 (p = 0.37), while the adolescents who were lost to follow-up in IYM tended to have higher BMI than adolescents who remained in the study (p = 0.06).
Beverage intake was reported only for weekdays, which may not represent usual intake, since it has been demonstrated that children eat differently on weekend-days compared to school days  and have a higher intake of soft drinks, but not fruit juice/cordial in the weekends . Thus, the intake of sweet drinks reported in the present study may be lower than the actual intake. Although other studies have found that the majority of sugar-sweetened beverages was consumed at home [21, 22] the children and adolescents reported a high intake of sweet drinks in the present study, and at least some of this was likely to be consumed in school. Moreover, the intake of fruit juice/cordial was assessed in a combined question and it was therefore not possible to get separate information on these two beverages. Furthermore, no information was obtained on intake of other beverages such as diet beverages, milk and water and we are therefore not able to determine whether the decreased intake of sweet drinks is associated with increased intake of other types of beverages.
A final limitation of the studies is that the questionnaires not have been formally validated in their current form. The questions were selected on the balance of validation evidence from current literature and the feasibility of measuring large number of children. Moreover, the majority of the questions was taken or adapted from previously validated and widely used surveys in Australia and New Zealand and pilot testing was performed with both questionnaires before their use in the program evaluations .