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INTRODUCTION
Adequate calcium intake is important for bone health and prevention of osteoporosis in later life. Inadequate consumption of calcium for a prolonged period can lead to bone loss and increased risk of osteoporosis [1]. The Korea National Health and Nutrition Examination Survey (NHANES) in 2009 reported a 4.8 times higher prevalence of osteoporosis in women aged 50 and over compared to men of the same age (38.7% vs 8.1%) [2].
One of the nutrition objectives of National Health Plan 2020 is 'to increase the proportion of individuals consuming adequate calcium to 30 percent by 2020' [3]. However, according to the results of the Korea NHANES (2013), Korean diets were especially deficient in calcium and provide only 71.1% of the recommended calcium intake [4]. When considering calcium intake by age and gender, adolescents, young adult women, and older adult women were found to consume much less calcium than recommended levels [4]. A previous study also showed that female college students consume only two-thirds of their recommended calcium intake [5].
Enough calcium should be consumed during adolescence or young adulthood in order to achieve peak skeletal deposition. To increase calcium intake, factors associated with eating behaviors in relation to calcium intake must be identified. Psychosocial theories that explain eating behaviors provide a framework for examining factors related to health or nutrition behaviors [6]. Social Cognitive Theory (SCT) is one such theory that has been used to explain nutrition behaviors. The basic premise of SCT is that cognition, behavior, and environment continuously influence each other, which necessitates consideration of these factors to explain behavioral determinants or design nutrition interventions. According to SCT, outcome expectations (beliefs), and self-efficacy are cognitive factors that provide motivation for behavioral changes [67]. Outcome expectations are the perceived consequences (positive, negative) of performing the behavior. Self-efficacy is defined as the perceived ability to perform the behavior and is known as an important predictor of nutrition behaviors [6789]. SCT has been used to identify factors that explain nutrition behaviors, such as fruit and vegetable consumption, breakfast consumption, whole-grain intake, and prevention of weight gain [10111213].
The purpose of this study was to determine if cognitive factors, including nutrition knowledge, outcome expectations, self-efficacy, and eating behaviors, differ according to calcium intake level in female college students, based on the consideration that their calcium intake is important for bone health and osteoporosis prevention in later life. In addition, calcium intake in young adult women is well known to be inadequate compared to the recommended intake level. Study findings will provide baseline information for developing nutrition education programs for college and young adult women to increase calcium consumption.
SUBJECTS AND METHODS
Subjects
A cross-sectional survey design was employed in this study. Subjects of this study were female college students attending university in Seoul, Korea. Investigators explained the study, and those who were willing to participate in the survey completed written informed consent. Subjects were also informed that they could withdraw from the study if they were not willing to respond to the questionnaire. Data were collected by self-report from 300 female college students in 2014. Excluding incomplete responses on calcium intake or other major study variables, data on 240 students (80% of completion rate) were used for statistical analysis. This study was approved by the Institutional Review Board of Seoul Women's University (IRB-2013A-3).
Measurement
The draft of the survey questionnaire was developed based on literature reviews regarding calcium intake and related factors among young adults or college students [81415161718192021222324252627]. After several revisions of the draft, the final survey questionnaire included items measuring general characteristics, calcium intake, nutrition knowledge, outcome expectations of consuming calcium-rich foods, self-efficacy in consuming calcium-rich foods, and eating behaviors.
General characteristics included age, grade, height, weight, and the attended colleges. Calcium intake was measured by a food frequency questionnaire, which surveyed the consumption frequencies and eating sizes of 20 foods contributing to calcium intake in women, based on results of the 2012 Korea NHANES [14]. Twenty food items were used, including milk, yogurt, cheese, tofu, beans, anchovy, perilla leaves, radish leaves, and seaweeds. Subjects were surveyed on how often and how much they usually eat each food item. Consumption frequency of each food was measured using 8 categories from 'never/rare' to '≥ 3 times/day' based on the Korea NHANES food frequency questionnaire. Size of each food item eaten was measured by comparison with the serving size of each food (e.g., 1 cup of milk). For this, subjects were asked to choose their regular eating size from four categories, 'small' (0.5 times of serving size for each food) to 'about two time the serving size'. Calcium intake for each food (mg/day) was calculated by multiplying the consumption frequency of each food (converted as frequency per day) by the corresponding size of each food eaten and calcium content in the serving size of each food (e.g., calcium content in one cup of milk, anchovy 15 g, etc.) based on the food composition data [151617]. Calcium intake for each food was summed up to represent calcium intake per day (mg/day).
Nutrition knowledge was measured using 20 items regarding general nutrition (8 items), calcium nutrition (6 items), and osteoporosis knowledge (6 items) [1819202122]. Nutrition knowledge included items on balanced diet, food sources of calcium or other nutrients, recommended amounts of calcium or energy intakes, risk factors, and prevention of osteoporosis. For each nutrition knowledge item, the number and percentage of correct responses by subjects were examined. Total score of nutrition knowledge was the summated score of correct responses for the 20 nutrition knowledge items.
Outcome expectations of consuming calcium-rich foods were measured based on 12 items. These included 7 health or practical benefits (e.g., osteoporosis prevention, healthy teeth, good taste, going well with other snacks or side dishes) and 5 negative expectations (i.e., disadvantages) of consuming calcium-rich foods (e.g., indigestion of dairy foods, bad taste, time to cook green vegetables, cost) [82324]. Each item was measured on a 5-point scale from 'strongly disagree' (1) to 'strongly agree' (5) to indicate the strength of each outcome expectation. Total score of outcome expectations of consuming calcium-rich foods was calculated by summing the 12 items while reversely coding the scores for negative expectation items of consuming calcium-rich foods. The higher total score indicates more positive or favorable expectations regarding consuming calcium-rich foods (Cronbach's alpha = 0.69).
Self-efficacy in consuming calcium-rich foods was measured using 10 items, including 'eating calcium-rich side dishes at meals', 'eating dairy foods for snacks', 'drinking dairy foods instead of soft drinks or caffeine beverages', and 'difficulty in eating calcium-rich foods because of cost' [82325]. Each item was measured on a 5-point scale from 'very difficult' (1) to 'very easy' (5) as a measurement of the perceived ability to perform each behavior. Total score for self-efficacy in consuming calcium-rich foods was calculated by summing the 10 items while reversely coding the scores for two negatively stated items. The higher total score for self-efficacy indicates higher perceived ability to consume calcium-rich foods (Cronbach's alpha = 0.75).
Eating behaviors covered 17 items, including 3 items related to eating right (diverse foods, adequate amounts of foods, regularity of meals), 8 items related to consumption of different food groups (e.g., grains, protein foods, vegetables, fruits, dairy products, green vegetables), and 6 items related to unhealthy behaviors (e.g., eating fatty foods, salty foods, sweets, and caffeine beverages) [82627]. Subjects were asked to select a frequency category of '0-2 days/week', '3-5 days/week', or '6-7 days/week'. For each eating behavior, numbers and percentages of subjects in each consumption frequency category were examined. To calculate the total score for eating behaviors, each item was coded from 1 (0-2 days/week) to 3 (5-7 days/week), and unhealthy behaviors were reversely coded. Total score for eating behaviors was the summated score of 17 items, with a higher score indicates more desirable eating behaviors (Cronbach's alpha = 0.73).
Statistical analysis
Data on 240 students were analyzed using SPSS (PASW statistics 18.0; SPSS Inc., Chicago, IL, USA). Descriptive statistics such as frequency, percentages, mean, and standard deviation were calculated. Subjects were categorized into two groups by calcium intake level, according to the recommended intake of calcium in women aged 19-29 years [28]. Thus, subjects in the high calcium intake group (HC) had a calcium intake of 650 mg or more per day, whereas those in the low calcium intake group (LC) had a calcium intake of less than 650 mg per day. To examine differences in factors, including nutrition knowledge, outcome expectations, self-efficacy, and eating behaviors by calcium intake level, t-test or χ2-test was used. Statistical significance was set at α = 0.05.
RESULTS
General characteristics of subjects by calcium intake level
Table 1 presents general characteristics of subjects. Mean age of subjects was 20.4 years. Mean height, weight, and body mass index (BMI) were 161.9 cm, 54.2 kg, and 20.7, respectively. Based on recommended calcium intake (650 mg/day for women aged 19-29 years) [28], subjects were categorized into low calcium intake group (LC, n = 187, 77.9%) or high calcium intake group (HC, n = 53, 22.1%). There was no significant difference in age, mean height, weight, or BMI between the HC and LC groups. About 30% of subjects were junior and freshman students, respectively, followed by sophomore (22.5%) and senior (19.2%) students. About half of subjects (48.8%) attended college of natural sciences, followed by college of social sciences (23.3%) and humanities (16.7%). Distribution of grade or attending college was not significantly different by calcium intake level (Table 1).
Nutrition knowledge of subjects by calcium intake level
Total score for nutrition knowledge was 13.5 on average (possible score: 0-20), which was 67.5 out of 100 (Table 2). Total score was not significantly different between the HC and LC groups. For each nutrition knowledge item, most subjects responded correctly regarding 'excessive intake of caffeine or soda and bone loss', 'whole grains and dietary fiber', 'food sources of proteins', 'food sources of vitamin A', and 'alcohol, smoking and osteoporosis'. In contrast, less than half of subjects answered correctly regarding 'food balance wheels', 'the recommended energy intake for young adults', 'adequate intake ratio of calcium and phosphorus for bone health', 'risk factor (body weight) and osteoporosis', and 'calorie comparison of foods'.
None of the nutrition knowledge items was significantly different between the HC and LC groups. Correct responses for some items, such as 'the recommended level of calcium intake for young adult women' (correct response: 84.9% in HC vs. 75.4% in LC), 'risk factor (body weight) and osteoporosis' (39.6% vs. 33.7%), and 'vegetable sources of calcium' (60.4% vs 53.5%), were slightly higher in the HC group than LC group, although there was no statistical significance by calcium intake level.
Outcome expectations of consuming calcium-rich foods by calcium intake level
Total score for outcome expectations regarding consumption of calcium-rich foods was 46.0 on average (possible score: 12-60), which was 76.7 out of 100 (Table 3). Total score for outcome expectations in the HC group was significantly higher than that in the LC group (47.3 vs. 45.6, P < 0.05).
Three out of 12 items were significantly different by calcium intake level (Table 3). Specifically, subjects in the HC group scored higher for benefits of consuming calcium-rich foods, such as 'milk or cheese is delicious' (P < 0.01) and 'dairy foods go well with other snacks' (P < 0.05), than those in the LC group. Scores for other practical benefits (e.g., dairy foods for quenching thirst, dairy foods for snack, green vegetables with other side dishes) were slightly higher in the HC group than LC group, although this difference did not reach statistical significance. Expectations regarding the health benefits of consuming calcium-rich foods, such as prevention of osteoporosis and healthy teeth, were not significantly different by calcium intake level.
Among the negative expectations of consuming calcium-rich foods, the item of 'eating dairy foods causes indigestion' was significantly different between the HC and LC groups (P < 0.001). Those with low calcium intake more strongly agreed with the expectation that eating dairy foods results in indigestion (e.g., diarrhea, abdominal pain).
Self-efficacy regarding consuming calcium-rich foods by calcium intake level
Total score for self-efficacy regarding consumption of calcium-rich foods was 34.5 (possible score: 10-50), which was 69 out of 100 (Table 4). Total score for subjects in the HC group was 36.4, which was significantly higher than that in the LC group (P < 0.01). For each self-efficacy item, subjects showed high scores for 'eating cheese or yogurt for snacks' (mean score of 4.1 in a scale of 1-5), 'eating dairy products every day', and 'drinking milk or yogurt instead of soft drinks or caffeine beverages' (mean score of 3.8).
Three out of 10 self-efficacy items were significantly different between the HC and LC groups. Subjects in the HC group scored significantly higher in terms of self-efficacy items such as 'eating cheese or yogurt for snacks' (P < 0.001), 'eating dairy products every day' (P < 0.01), and 'eating calcium-rich side dishes when I have a meal' (P < 0.05) compared to those in the LC group. Those with high calcium intake also showed higher scores for self-efficacy of eating calcium-rich foods in situations such as eating alone and eating with others, although there was no significant difference in these self-efficacy items by calcium intake level.
Eating behaviors of subjects by calcium intake level
The total score for 17 eating behaviors was 33.9 (possible score: 17-51) on average, which was 66.5 out of 100 (Table 5). Total score was slightly higher in the HC group than LC group, although it did not reach statistical significance (34.8 vs. 33.6).
Seven out of 17 eating behavior items were significantly different by calcium intake group. The percentage of subjects who consumed 'dairy foods once or more per day' almost every day (6-7 days/week) was significantly higher in the HC group than LC group (43.4% vs. 18.3%, P < 0.001). Other eating behaviors contributing to calcium intake were also significantly different by calcium intake level. The percentage of those who consumed seaweeds frequently (≥ 3 days per week) was 39.6% in the HC group and 28.5% in the LC group (P < 0.05). Subjects in the HC group also consumed anchovy more frequently; 11.3% of the HC group and 2.2% of the LC group ate anchovy or dried strip of icefish 6-7 days per week (P < 0.05). Consumption of green vegetables, such as pepper leaves, leaf beat, and broccoli, was also more frequent in the HC group than LC group (P < 0.05). The percentage of those who consumed 'protein foods more than two meals per day' almost every day was 39.6% in the HC group compared to 22.5% in the LC group (P < 0.05). The percentage of those who ate fruits or fruit juice almost every day was 35.8% in the HC group and 18.7% in the LC group (P < 0.001).
Among six unhealthy eating behaviors, only 'eating sweets or soft drinks' was significantly different by calcium intake level (P < 0.01). About 37% of the HC group compared to 16.2% of the LC group ate sweets infrequently (0-2 days/week).
DISCUSSION
This study examined the cognitive factors, including knowledge, outcome expectations, self-efficacy, and eating behaviors, in relation to calcium intake based on SCT. In this study, only 22.1% of subjects consumed the recommended level of calcium, indicating that most subjects had insufficient calcium in their diets. Mean intake of calcium by subjects in this study was 464.1 mg (not presented in Table), which was 71.4% of the recommended intake for calcium [28]. The study result was similar to that of the Korea NHANES (2013), wherein women aged 19-29 years consumed 69.4% of the recommended calcium intake [4]. Hong et al. (2012) [29] also reported that calcium intake by college female students was 74% of the recommended level, with significant differences among groups by bone mass (527.9 mg/day in the normal group, 488.8 mg/day in the osteopenia group, and 479.5 mg/day in the osteoporosis group). In a study by Yu et al. (2013) [30], calcium intake by Koreans was lower than that by Americans in all age groups examined, especially adolescents. These results raise concerns that calcium intake by young adult women is deficient and needs to be increased for bone health. A study on female college students [31] also reported that 27% of students were at risk for osteopenia or osteoporosis. In the current study, major foods contributing to calcium intake were mainly dairy products (milk 25.0%, ice cream 10.0%, yogurt 7.6%, and cheese 5.1% of calcium intake) and anchovy (6.5%, not presented in Table). Therefore, practical tips for consuming dairy foods or anchovy need to be developed to increase calcium consumption in young adult women.
The study results show that nutrition knowledge of subjects had a score of 67.5 out of 100. In a study on college students, Kim (2012) [19] reported that mean score of nutrition knowledge scored 6.7 out of 15 (44.9 out of 100). Other studies on college students also reported a nutrition knowledge score of 10.8 out of 20 (54.2 out of 100) [32] and osteoporosis knowledge score of 12.7 out of 20 (63.5 out of 100) [18]. A study on female osteoporosis patients [20] showed that osteoporosis knowledge (risk factors, food and nutrition, etc.) scored 19.8 out of 27 (73.3 out of 100). Zhang & Chandran [22] measured osteoporosis knowledge in nurses and reported a mean knowledge score of 14.5 out of 20 (72.5 out of 100). Since the nutrition knowledge measure in the current study was developed for this study based on literature reviews, it is not possible to directly compare the knowledge results to other studies. Nutrition knowledge in this study was slightly higher than that of previous studies on college students [193233], although the nutrition knowledge of subjects was still inadequate. Nutrition knowledge, either total score or each knowledge score, was not different by calcium intake status. Nutrition knowledge items in this study were composed of items on general nutrition, calcium nutrition, and osteoporosis knowledge. Subjects were knowledgeable in relation to general nutrition (e.g., food sources of nutrients) and risk factors (caffeine, alcohol) of osteoporosis. In contrast, many subjects answered incorrectly regarding specific nutrition knowledge, such as adequate energy intake for young adults, adequate intake of minerals for bone health, and energy comparison of foods. Due to increased use of the web and other IT sources, it is likely that college women obtain their nutrition information from these sources as well as from books or classes. However, it seems that college women did not know the specifics of nutrition knowledge for calcium nutrition or osteoporosis prevention. Study findings also suggest that nutrition knowledge might not be enough to promote healthy behavior, which was calcium consumption in this study.
The total score for outcome expectations (76.7 out of 100) suggests that subjects had slightly favorable expectations regarding consumption of calcium-rich foods. Subjects with high calcium intake hold more positive expectations towards consuming calcium-rich foods compared with those with low calcium intake (P < 0.05). College women with high calcium intake felt more strongly about the practical benefits of calcium intake, such as 'taste of milk or cheese' (P < 0.01) and 'dairy foods go well with other snack foods' (P < 0.05). Taste is the major determinant in food selection. In contrast, health benefits (e.g., osteoporosis prevention, healthy teeth) were not significantly different between the HC and LC groups. College women in both groups perceived health benefits similarly, as shown in Table 3. Similar to the current study, previous studies on children, young adults, or older adults [81234] also reported a significant relationship between practical advantages (e.g., taste, convenience to cook) and healthy eating behaviors (e.g., eating fruits and vegetables). The current study suggests that nutrition education for college women needs to focus on the practical benefits of consuming calcium-rich foods, such as taste and going well with other snacks.
With respect to the disadvantages of consuming calcium-rich foods, 'eating dairy foods cause indigestion' was the belief that differentiated those in the HC group from those in the LC group. Lactose intolerance is common in Asians compared to Caucasians. However, there might be several ways to deal with lactose intolerance, including choosing lactose-free or lactose-degraded milk, drinking small servings of milk each time, eating milk with other foods (e.g., bread, crackers), and choosing other dairy foods (e.g., cheese, yogurt). Nutrition educators might provide several tips for consuming milk for those with lactose intolerance.
In this study, young adult women in the HC group showed significantly higher self-efficacy in consuming calcium-rich foods than those in the LC group (P < 0.01). As suggested in previous studies [5233435], the current study supports the importance of self-efficacy in performing healthy eating behaviors, including eating dairy foods, fruits, and vegetables as well as reading nutrition labels. Self-efficacy in this study was measured by perceived confidence in doing specific behaviors or performing behaviors in specific situations (e.g., eating out, eating with others). Results on each self-efficacy item suggest that the two groups differed in perceived confidence of performing specific behaviors, such as eating dairy foods regularly, eating dairy foods for snacks, and eating calcium-rich side dishes at meals. These findings suggest that teaching strategies to increase the perceived ability of performing specific, simple behaviors (e.g., eating one or more dairy foods every day, eating yogurt as snacks) might be useful in nutrition education to increase calcium intake. In contrast, there was no difference in the perceived ability to eat calcium-rich foods in specific situations, such as eating out and eating with others. Results for these self-efficacy items (possible score: 1-5, mean score 3.2 for eating out, 3.1 for eating with others) indicate that the perceived ability to consume calcium-rich foods was not high in social situations. Therefore, college women should learn the methods for choosing calcium-rich foods in social eating situations. Contrary to previous studies [35], perceived constraints of cost or time were not barriers to calcium intake.
The study results show that eating behaviors in general or consumption of food groups were not desirable in the current study. Eating behaviors such as eating a variety of foods, eating adequate amounts, and eating meals regularly were not significantly different by calcium intake level. A previous study on college women [36] also reported problems such as irregular meals, skipping meals, eating speed, and eating late at night.
With respect to consumption of food groups, several differences in eating behaviors were noted by calcium intake status. College women in the HC group, showed more desirable behaviors in eating dairy foods (P < 0.001), anchovies, seaweeds, green vegetables, and protein foods (P < 0.05) than those in the LC group. Foods in these food groups are major sources of dietary calcium, and thus more frequent consumption of these foods contributes to higher calcium intake. This study also showed that those with high calcium intake exhibited more desirable eating behaviors, such as eating fruits more often (P < 0.001) and having sweets or soft drinks less (P < 0.01). Song et al. [37] reported that the traditional meal group (e.g., healthy eating) showed higher intakes of nutrients (e.g., proteins, iron, and vitamin A) and higher bone mass compared to the modified group (e.g., like to eat noodles, bread, fast food, snack, etc.). Studies on nutrient intakes [383940] have reported that intakes of calcium, protein, iron, and vitamins contribute to bone mass, suggesting the importance of modifying eating behaviors.
In conclusion, this study examined the factors related to calcium intake by applying theoretical background (SCT) and revealed that those with high calcium intake had more favorable outcome expectations, higher self-efficacy in consuming calcium-rich foods, and more desirable eating behaviors. However, there was no difference in nutrition knowledge by calcium intake level. Based on this study, nutrition education for college women needs to modify personal expectations of consuming calcium-rich foods, increasing self-efficacy in consuming calcium-rich foods, and changing specific behaviors for increased calcium intake. More specifically, nutrition education might focus on practical benefits of eating calcium-rich foods (e.g., taste, for snack foods, convenience, etc.) as well as health benefits. Nutrition education should also incorporate methods for increasing perceived confidence to consume calcium-rich foods (e.g., eating dairy foods regularly, eating dairy foods for snacks, eating high-calcium side dishes at meals). Perceived self-efficacy might be increased through step-by-step performance of eating behaviors, observing others' healthy behaviors, and praise or persuasion [7]. These methods could be used to plan nutrition education for college women. To modify eating behaviors for calcium intake, behavior modification skills such as monitoring, goal setting, stimulus control, behavior substitution, and reinforcement might be employed in nutrition education for college women.
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