Children in this study were on average lean, with a mean (SD) BMI z-score of 0.2 (± 1.4), and waist circumference of 52.2 (± 6.0) cm. Fifty-three percent were non-Hispanic white, 16.2% were African-American, 14.0% were Hispanic-American, 2.9% were Asian-American, and 13.2% identified themselves as “other.” Across meals, children consumed 23.9 (±31.1) kcals from milk (both white and chocolate) and 37.6 (±38.0) kcals from sweetened beverages (all juices, juice drinks, and cola).
The primary aim of the study was to determine if sweetened beverage and milk/calcium intakes are inversely correlated with one another in a laboratory meal setting. Findings from these test meals show that intake of sweetened beverages (cola, juice, and juice drink) was negatively associated with intake of not only milk, but also calcium and vitamin D, two essential micronutrients. Specifically, sweetened beverage intake was negatively associated with intakes of both milks together (chocolate and white) (r = −0.32, p < 0.01), and with intake of just white milk (r = −0.20, p = 0.02). Also, sweetened beverage intake was negatively associated with total calcium consumed at the test meals (r = −0.24; p < 0.01). This relationship was stronger after adjusting sweetened beverage intake for total calories consumed at the meals (r = −0.38; p < 0.001) .
Intake of sweetened beverages (kcal), adjusted for total kcal consumed at the test meals, was negatively associated with total meal calcium (mg) (r = −0.38; p ≤ 0.001).
In addition to having a negative relationship to calcium intake, sweetened beverages were also negatively associated with amount of vitamin D consumed (r = −0.28; p < 0.05). All of the above relationships remained after adjusting for child age, gender, and ethnicity.
While these findings are cross-sectional and do not demonstrate a causal relationship, they lend support to the notion that sweetened beverages displace intake of milk in children’s diets. The possibility that children who over-consume sugar-sweetened beverages may do so at the detriment of essential nutrients such as calcium and vitamin D warrants further investigation. In other reports, increased soft drink consumption, in particular, has been associated with lower intakes of calcium and other micronutrients in children and adolescents (7
). This is of great nutritional concern because calcium and vitamin D work together as key nutrients in achieving optimal bone health (8
). Further, Zemel and colleagues have observed that adding calcium to the diet can enhance weight loss (10
) and improve metabolic profiles (21
) in adults. In addition to its potential to displace calcium, consumption of sweetened beverages alone has been proposed as an independent risk factor for obesity because some studies have found that children do not compensate for energy consumed in these highly palatable sources of liquid calories (22
). Taken together, one can hypothesize that sweetened beverage consumption might be a contributing risk factor to poor overall diet quality and, potentially, obesity.
Previous reports have demonstrated that intake of sweetened beverages increases as children grow older, while intake of milk tends to decrease (3
). Accordingly, a secondary aim of this project was to test for these associations in the laboratory. Indeed, child age was positively associated with sweetened beverage intake (r = 0.27; p < 0.01) and this association remained after adjusting for total energy intake (r = 0.19; p < 0.05). Further, after adjusting for total energy intake, age was negatively correlated with calories from both milks (white and chocolate) (r = −0.22; p < 0.01). While these relationships were expected, it was surprising that such low intakes of milk were seen in children that were, on average, not yet 5 y. old and who consumed the meal with their mothers present. Average caloric consumption from milk at the meal was around 24 kcal (~15 milliliters) and intake of calcium was around 200 mg. If this is representative of children’s usual consumption, the recommended adequate intake of 800 mg/day for this age group (25
) would not be achieved. While other reports have noted similar results, most studies have identified this trend in adolescents (3
) or children older than 5 y. of age (23
). Results from the present study suggest that younger children may be at risk for this dietary trend as well, but additional studies are warranted to determine how well this test meal predicts children’s usual intakes.
Previous cross-sectional (12
) and experimental (10
) studies have suggested that calcium can be protective against obesity, despite a lack of relationship in this study. Neither calcium nor milk intake was inversely associated with BMI z-score (p-values ranging from 0.30–0.80), or with waist circumference (p-values ranging from 0.13–0.53). However, children were young and positive effects of calcium on body weight may not be evident yet. Also, sweetened beverage intake (adjusted for milk intake) was not associated with BMI z-score (p = 0.61) but showed a modest positive association with child waist circumference (r = 0.18, p = 0.05). These intriguing findings should be interpreted with caution. Intake of a test meal may not reflect children’s usual intake, and thus foods and nutrients consumed at these meals may not be good predictors of long-term consumption or health risk.
There are several factors that might have influenced children’s food choices at the test meal that were not taken into account in this study, but should be noted. First, maternal beverage consumption patterns may influence children’s beverage choices, but these were not factored into the present study design. Fisher et al.
found that maternal milk consumption is positively associated with daughters’ milk intakes (26
). It is possible that children’s beverage choices in the present study were in part mediated by mothers’ habitual beverage consumption, thus future studies might wish to control for this variable. Furthermore, Birch and colleagues have hypothesized that parental feeding styles that are overly restrictive can encourage overeating of “restricted” foods in free access situations, particularly in young girls (27
). It may be that children preferred to drink sweetened beverages at the laboratory because they were not regularly offered these beverages at home. The fact that calcium intakes in these meals were low is concerning, given that mothers were present, and this suggests the need to conduct future research on assessing level of parental concern and awareness about this important nutrient.
In addition to the parental variables mentioned above, there were other limitations. First, a laboratory meal might not reflect children’s usual intakes, as discussed above. Although the lab setting provided was comfortable for families, the laboratory cannot substitute for children’s natural eating environments. Furthermore, day-to-day and meal-to-meal fluctuations in calcium intake are common in children. Because this study presents data from only two meals, results may not reflect overall patterns of calcium consumption. Second, while children were offered a range of foods, intakes were limited by the choices available. The number of calcium-rich foods offered to children was minimal, and the possibility that greater calcium intake would have been seen with a greater variety of calcium-containing foods cannot be eliminated. Finally, power analyses were not performed on the reported relationships, so it is not possible to rule out the presence of a Type II error in the data. Despite the limitations, this is one of the only laboratory feeding studies to corroborate a wealth of cross-sectional data. Further, there is a lack of observational food intake data on children this age, so the contribution to the literature is thought to be meaningful.
These findings support previous cross-sectional data, and suggest that intake of sweetened beverages and intake of micronutrients such as calcium may be inversely correlated with each other during meals. Because this study was not designed to test causality, future investigations are warranted to determine the implications for consumption of sweetened beverages in the overall diet. Reducing consumption of sweetened beverages in children’s diets might be one strategy for increasing milk and calcium intake, a notion that warrants future testing.