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UBC Theses and Dissertations

Factors associated with calcium intake in adolescent athletes Webster, Brenda L.


This study investigated dietary calcium intakes, and factors potentially affecting them, in adolescent athletes of both genders competing in either an aesthetic sport (gymnastics) or non-aesthetic sport (speed skating). For all athletes, data collection was conducted using a self-administered questionnaire which assessed the following: estimated calcium intake using a validated food frequency questionnaire, pubertal status, demographics (age, gender, racial origin, use of vitamin/mineral supplements, employment, allergies to milk or dairy products, parental socioeconomic status),training volume, competitive level, and social environmental factors (differential association (i.e. family, friends, health experts, media), lifestyle, dieting behaviour, modelling behaviour and social and non-social reinforcement). Body composition was assessed using skinfold measurements. The athletes competed at a minimum of a provincial level in either gymnastics (males =25, females =32) or speed skating (males =32, females =25). The mean ages of the male athletes were similar for the two sports (14.4 ± 1.8 yrs, 3i ± SD vs14.7± 1.9 yrs for skaters and gymnasts respectively); however, the skaters were taller (170.2 ± 10.3 cm vs. 158.5 ± 13.0 cm, p <0.05), heavier (60.5 ± 11.9 kg vs50.1 ± 12.5 kg, p <0.05) and had higher estimated percent body fat (%13F)(8.0 ± 3.4% vs. 3.7 ± 2.1%, p <0.001) and sum of skinfold measurements (S4SF)(35.8 ± 9.8 mm vs. 23.9 ± 3.6 mm, p <0.001). Similar to the males, the mean ages of the female athletes were similar for skaters and gymnasts (14.3 ± 1.6 yrs vs. 14.1 ±1.6 yrs); however, the skaters were taller (162.2 ±8.2 cm vs. 153.6 ± 4.9 cm, p < 0.001), heavier (58.5 ±9.5 kg vs. 45.2 7.9 kg, p < 0.001) and had higher estimated %BF (21.0 ± 7.7% vs. 9.4 ± 5.7%, p <0.001) and S4SF (65.5 ± 18.9 mm vs. 38.5 ± 12.3 mm, p <0.001). A 2X2 ANOVA (gender X sport) was used to assess differences in total dietary calcium intake. The analysis showed that there was a significant main effect of sport (F1100 = 6.63, p =0.01), indicating that averaged over gender, the skaters had significantly higher calcium intakes than the gymnasts. There was no main effect of gender (F1,100 = 2.90, p =0.09) and no interaction between gender and sport (F1,100 = 0.52, p = 0.47), meaning that the difference in calcium intake between the two sports was similar for both genders. Additionally, all groups of athletes exceeded the recommended nutrient intake for calcium. Among the independent variables, 2X2 ANOVA (gender by sport) revealed significant main effects for scores on the dieting sub-scale and for social reinforcement score. A significant main effect of gender was detected for scores on the dieting sub-scales (F1,105= 21.86, p <0.001), meaning that averaged over the two sports, the female athletes scored significantly higher than the male athletes. No significant effect of sport was detected, nor was an interaction effect detected. Although a gender difference existed for the dieting sub-scale scores, neither the mean scores of the male nor the female athletes suggested tendencies towards disturbed eating behaviours. ANOVA of the social reinforcement variable showed that there was a significant main effect of sport (F1,107 = 5.78, p = 0.02), indicating that while athletes in both sports disagreed that consuming milk evoked positive feelings and a sense of belonging to a group, the gymnasts exhibited stronger disagreement to the statements. No significant effect of gender was detected, nor was there an interaction effect. Stepwise forward entry multiple regression analysis (MRA) was used to determine the variable(s) which best predicted total dietary calcium intake. Two models were analyzed using MRA, a Traditional Model which included age, gender, %BF, weight and sport, and a Social Model which included dieting sub-scale score, differential association score, social and non-social reinforcement scores, modelling behaviour score, and a lifestyle score. The analysis showed that for all athletes combined, only one variable from the Social Model (social reinforcement) and one variable from the Traditional Model (sport) significantly explained variance in total dietary calcium. Each variable explained 6% and 10% of the variance in the dependent variable respectively. When the athletes were divided by sport and gender, different relationships emerged. For the male athletes, only differential association could significantly predict total dietary calcium intake, explaining 9% of the variance in the dependent variable. For female athletes combined, only one variable from the Social Model (modelling behaviour) and one variable from the Traditional Model (sport) entered the predictive equations, explaining only 9% and 15% of the variance in calcium intake, respectively. For the female skaters, differential association explained 21 % of the variance in the dependent variable, while for the female gymnasts, non-social reinforcement explained 18% of the variance in total dietary calcium intake. The results from this study show that for all athletes combined, variables from neither the Social nor Traditional Models were strong predictors of total dietary calcium intake. The social variables explained more variance in the dependent variable than the traditional variables only when the athletes were divided by gender and sport, and still approximately 80% of the variance was left unexplained Therefore, the variables studied were not predictors of total dietary calcium intake in these athletes.

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