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Original Research |
University of Hawaii at Manoa, Honolulu, Hawaii (R.N.)
Purdue University, West Lafayette, Indiana (C.B.)
New Mexico State University, Las Cruces, New Mexico (M.A.B.)
Washington State University, Pullman, Washington (L.P.)
Colorado State University, Fort Collins, Colorado (G.A.)
University of California, Davis, Davis, California (C.M.B.)
University of Idaho, Moscow, Idaho (K.G.)
Utah State University, Logan, Utah (D.G., J.K.J.)
University of Arizona, Tucson, Arizona (S.M.)
University of Nevada, Reno, Nevada (M.R.)
Address reprint requests to: Rachel Novotny, PhD, RD, Professor, University of Hawaii at Manoa, 1955 East-West Rd., Honolulu, Hawaii 96822. E-mail: novotny{at}hawaii.edu
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ABSTRACT |
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Methods: Cross-sectional survey with two 24-hour dietary recalls one week apart. Calcium intake was evaluated in 167 male and female adolescents of Asian, Hispanic and white ethnicity, ages 10–18 years, from six states. Main outcome measures were mean daily calcium intake (mg/day). Statistical analyses performed: t tests, Chi-square and analysis of variance for differences by age, ethnicity and gender, multiple regression of factors influencing calcium intake.
Results: Overall median calcium intake was 938 mg/day with 868 mg/day for Asians, 1180 mg/day for whites and 896 mg/day for Hispanics. Daily milk intake was the primary predictor of calcium intake with Asian ethnicity and female gender each showing a negative association to calcium intake in multiple regression models.
Conclusions: Milk intake was the primary factor positively influencing calcium intake, while Asian ethnicity and female gender negatively influenced calcium intake. Thus, interventions to improve calcium intake should focus on improving milk intake of Asians and females.
Key words: dietary calcium, youth, Hispanic, Asian
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INTRODUCTION |
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The Dietary Reference Intakes (DRI) for calcium were established in 1997, taking into consideration levels needed to prevent future osteoporosis [8]. At present, there is insufficient evidence to establish an Estimated Average Requirement (EAR) from which a Recommended Dietary Allowance (or RDA) would be determined; therefore, an Adequate Intake (AI) level was established, based on maximal calcium retention for different age groups [7]. The AI for children, ages four to eight years, and adolescents, ages nine to 18 years, is 800 mg/day and 1300 mg/day, respectively. At this time, the AI levels are the same for male and female children due to insufficient data to establish separate levels. Therefore, the AI levels for calcium have not been adjusted for differences that may occur with body size or pubertal development.
Calcium Intake of Ethnic Populations
According to the Healthy People 2010 Objectives Report [9], 46% of persons age two years and older were at or above the calcium recommendation from 1988–1991 (calcium from foods, dietary supplements and antacids). Data from NHANES III show that 52% of males and 19% of females, ages nine to 19 years, met the 1989 RDA for calcium. The NHANES III survey also provided information on calcium intakes of adolescents among ethnic groups that included "Non-Hispanic Black, Mexican Americans, and Non-Hispanic White" [10]. Adequate information on American Indian/Alaska Native and the total Hispanic population is not available from this survey. Data on calcium intake were considered "statistically unreliable" for Asians, Pacific Islanders and Native Hawaiians due to small sample size [9]. The CSFII 1994–96 survey also provided limited information on mean calcium intake of adolescents by ethnicity (Hispanic vs. non-Hispanic only) [11], but calcium intake was not provided for Asians as a separate group.
Some study results have indicated variation in calcium intake among adolescent ethnic groups [12–15]. In order of highest to lowest calcium intake, the following ethnic groups were studied: Caucasian, Hispanic, Puerto Rican, Mexican American, Mixed/Other (ethnic origin of the Indian Subcontinent), Cuban, African American and Asian. Two studies identified Asians as the ethnic group with the lowest calcium intakes [12,13].
There is limited information on calcium intake and calcium food sources of Asians and Hispanics. Wang et al. [13] obtained calcium intake information using a food frequency questionnaire that had been validated only on white women. A food frequency questionnaire was also used by Barr [12], but it did not include Asian foods. Asian calcium intake appears to be considerably lower than white calcium intake, although this finding remains questionable due to problems with dietary methodology with these studies.
Calcium Sources and Their Bioavailability
Based on adults Chinese and Japanese in Hong Kong and Japan, respectively, Asians consume 23% to 24% of their diet from dairy products [13]. In white populations, this value has been estimated at 70% [14].
Bioavailability (availability of calcium for absorption by the intestines) of calcium from other sources is generally much lower than from dairy products [14]. Key dietary factors that decrease absorption include phytates (found in most cereals and seeds), oxalates (found in spinach, rhubarb, walnuts and sorrel) and tannins (found in tea). These compounds form insoluble complexes with calcium, reducing its absorbability. Some factors that increase calcium absorption are lactose, proteins and phosphopeptides. However, at the kidney, phosphorus, excess protein and sodium increase calcium loss in the urine.
Calcium Intake by Age and Gender
The Continuing Survey of Intakes by Individuals (CSFII) 1994–96 compared mean calcium intake for males and females with recommended levels. Mean calcium intakes for males and females ages nine to 18 were significantly below the 1300 mg/day AI recommendations for calcium [18]. Daily calcium intake from other national studies (NHANES I 1971–74, NFCS 1977–78, NHANES II 1976–80, CSFII 1985–86, NHANES III 1988–91, and CSFII 1989–91) show a decline in calcium intake in both males and females of this age group over a 20 year period [12]. A decline in mean calcium intake was noted in females between six and 11 years old (865 mg/day) and 12–19 years old (773 mg/day) [19]. The converse was true in males where intakes tended to increase with age (6–11 years old: 984 mg/day and 12–19 years old: 1145 mg/day).
According to the CSFII 1994–96 survey and NHANES II data, overall calcium intake tends to be slightly higher in the older age group than in the younger. Eck and Hackett-Renner [16] presented calcium intake by age and gender. Calcium intake by age and gender does not appear to be different in either of these studies, although a widening gap between males and females at the older age is indicated. According to the CSFII 1994–96 survey, males tend to have a higher calcium intake than females (from age six up) [19]. Eck and Hackett-Renner [16] and Looker et al. [17] examined calcium density (calcium/kcal), although Looker et al. [17] did not present the adjusted data. Eck and Hackett-Renner [16] showed that calcium intake was similar for males and females after adjustment for energy, though this was not statistically tested.
When making nutrient comparisons between age and gender groups, it is important to consider differences that may occur with body size and, therefore, energy intake. Since adolescent males consume greater quantities of food than females relative to their body size [25], it is more likely they will meet the DRI for calcium. Female caloric intakes are lower, so that adolescent females must make careful food selections to meet the DRI for calcium.
Food Sources of Calcium
Milk consumption decreased 36% from 1965 to 1996, accompanied by an increase in soft drink and non-citrus juice consumption in the United States [20]. According to Gerrior et al. [21], 73% of the calcium available in the food supply was from milk and milk products in 1994. A shift in sources of calcium in the food supply toward cheese and lower fat milk was seen from 1970–1994. Other calcium contributors in the food supply were vegetables and legumes (10%), grains (5%), meat, poultry and fish (5%), and other sources (7%). In 1990–92, females ages 11–18 obtained 48% of their calcium from milk and milk products, 16% from mixed dishes, 14% from grain products and 22% from other sources [22]. Amount consumed (g) and sources of dairy products (e.g., milk, yogurt) were compared by age and gender in the CSFII 1994–96 survey, but not as a percent of total calcium intake or by ethnic group.
Wang found differences in food and beverage sources of calcium by ethnic group [15]. Low fat milk was selected by whites more frequently than by African Americans; bread and cereals were important sources of non-dairy calcium for Asians and Hispanics. Vegetables and legumes were a major source of non-dairy calcium for Asians, who generally had low dairy consumption [15].
Few studies discuss calcium food and beverage sources consumed by the Asian population and none in the adolescent age group. A study done in Japan by Imaeda et al. [23] summarized the top ten calcium food and beverage sources in the diets of middle-aged Japanese men and women. Whole milk was the top source followed by tofu, eggs, koji miso (soybean paste), white bread, aburage (fried soybean curd), daikon (Japanese radish), spinach, well-milled rice and cabbage. Although calcium content may have placed these sources in the top ten, the calcium bioavailability varies considerably among these foods.
Bioavailability of Calcium
Several dietary factors can affect the bioavailability and excretion of calcium. Phytates, found in cereal bran, legumes and seeds, can reduce absorbability of calcium by forming an insoluble complex with calcium [24]. Oxalates may also form complexes and are found in spinach, rhubarb and walnuts. Excess protein, specifically protein containing sulfur amino acids, can increase acidity in the blood, causing increased excretion of calcium [24]. Sodium shares a similar transport system in the kidney as calcium, which can result in increased calcium excretion if excessive sodium is consumed.
Objective
The primary objective of this study was to describe variation in calcium intake among Asian, Hispanic and white males and females 10–18 years of age. Specifically, this study examined the association of calcium intake with age, gender and ethnicity. The relationship between ethnicity and calcium intake was also examined by calcium food sources.
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METHODS |
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Study Design
Each participant completed two 24-hour dietary recalls scheduled approximately one week apart. In scheduling the appointments, an attempt was made to collect approximately 75% of the recalls as weekdays and 25% as weekend days. For 30 (18%) volunteers the two days each represented a weekend. The two days represented a weekday and weekend for 40 (24%), and the remainder represented two weekdays for 97 (58%).
Dietary Methodology
Twenty-Four-Hour Dietary Recalls.
The 24-hour dietary recall method used in the Continuing Survey of Food Intakes by Individuals (CSFII), 1994–1996 was modified for use in this study. Researchers used the CSFII Day 1 and Day 2 Intake Questionnaires guide to promote a consistent interview style among the interviewers and to increase the use of neutral probes to avoid influencing the participants’ responses. Interviewers conducted each recall as a face-to-face interview. Food models, measuring cups and spoons, rulers, concentric circles, and various-sized bowls, glasses, cups, and plates were used to assist with portion size estimates. One investigator (KJ) conducted the training for the modified CSFII protocol among the investigators of the six study areas via multi-site conference calls in June 1999. Each site investigator trained interviewers in the protocol.
A four-pass method was used where the four passes included 1) the creation of a quick list of foods along with the time they were consumed, 2) a detailed description of the foods and the amounts consumed, 3) the name of each eating occasion and the location from which the foods were obtained, and 4) a review of the food intake. At the end of the interview, interviewers made assessments regarding usual food intake, dieting status, vitamin and mineral supplementation, food allergies or intolerances and alcohol consumption. Participants were asked to use mental imagery and chronologically recount the previous day’s events and activities in order to help them remember where, when and what they ate [9].
Nutrient Database.
All dietary recalls were checked by a Registered Dietitian (KJ) prior to being analyzed using The Food Processor® computer program (Version 7.6, 2000, ESHA Research, Salem, Oregon). To ensure that the most accurate calcium value was assigned to each food reported during the recalls, the calcium value for each food from the ESHA software was compared with the companion value from the USDA Nutrient Database for Standard Reference. If brand names were reported, the calcium value from ESHA was used only if the manufacturer had supplied a value other than zero or missing. Some low-calcium foods did not have a calcium value reported by either USDA or a manufacturer. These missing values were considered negligible and were ignored. Recipes were created for foods that we could not find in the ESHA database (e.g., homemade stir fry). A total of 5,255 foods were recorded from the recalls.
Data Analysis
Each food item included a serving size, a gram weight, an energy value, a calcium value, and calcium density values per 100 grams and per 100 kcal of food. Foods were sorted, and they were assigned to food groups. Data were analyzed by the Statistical Package for the Social Sciences® Version 8 (SPSS Inc, Chicago Illinois). Subgroup analyses were performed by gender, age and ethnic group. Subgroup analyses included t tests and analysis of variance as well as multiple regression of factors influencing calcium intake. Soda intake (mL/day), daily calcium intake (mg/day), water intake (mL/day) and calcium from milk intake (mg/day) were not normally distributed and were transformed using the natural logarithm, except soda which was transformed with the square root.
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RESULTS |
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Calcium density in volume (CDV, calcium/100 g food) was 47.8 ± 22.2 mg/100 g food and in energy (CDE, calcium/100 kcal food) was 50.4 ± 19.9 mg/100 kcal (Tables 2 and 3). Neither expression of calcium density differed by gender, but CDV differed by age group and ethnicity, where the younger children ate more calcium dense diets than the older children and white children ate more calcium dense diets than Asian children (Table 2). CDE differed among ethnicities where white children had more calcium dense diets than Hispanics (Table 3). Energy intake was not different among the ethnic groups (2165.5 ± 719.7 kcal).
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Calcium intake from milk also differed among ethnic groups (364 ± 320 mg/day for Asians, 469 ± 488 mg/day for whites and 247 ± 226 mg/day for Hispanics, F = 4.30, p = 0.02). Post-hoc tests in calcium intake from milk between ethnic groups revealed variations were due to differences between white and Hispanic intake. Energy contribution from milk and servings of milk were not different among ethnic groups.
Other Beverage Intake
A larger proportion of the older children consumed one or more cans of soda per day than the younger children (43% vs. 32%, 
2 = 8.75, p = 0.013). Among the three ethnic groups, the Hispanic youth were more likely to consume one or more cans of soda per day (61%) compared to the Asian (29%) and white (36%) (2 = 16.607, p = 0.002). There were no differences in soda consumption between males and females. Water intake was higher among the older age group than the younger (397 ± 279 mL/day vs. 223 ± 118 mL/day, t = -5.44, p = 0.000) and no differences were detected among the ethnic groups.
Multiple Regression
A multiple regression analysis of factors influencing mean daily calcium intake showed that milk intake overwhelmed all other variables in predicting calcium intake such that only milk is significant in the model (Table 4). A model with the core demographic variables of this study showed that Asian and Hispanic ethnicity and female gender were negatively associated, while age did not significantly contribute.
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DISCUSSION |
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Calcium Intake by Age and Gender
There were no age group differences in calcium intake per day, though females consumed less calcium than males. Still, when adjusted for energy intake, differences between genders disappeared. The recommended intake is the same for males and females, so females will have to consume calcium dense foods to obtain sufficient calcium without consuming excess energy. In the CSFII 1994–96 survey, calcium intakes were also higher among males than females (unadjusted for energy).
Soda and water displaced milk in the older age group in comparison to the younger one. Peer influences to consume "cool drinks" (e.g., soda, sports drinks), matching of beverages with meals (e.g., burgers with soda rather than milk), and availability/cost are several factors that can affect consumption of calcium foods and beverages [26].
Ethnic Differences
The white children consumed more calcium than the Asian children or Hispanic children, apparently due to selection of more calcium dense foods. Hispanics consumed less calcium per kcal, while Asians consumed less calcium per gram of food, compared with whites. When compared with other studies that have included Asians as a sub-population [14,15], our calcium intakes were high. Earlier studies may have failed to assess Asian calcium intakes completely as they used food frequency questionnaires that had not been developed for Asians. Using a standard method (CSFII) for obtaining 24-hour recalls and use of plastic food models/measuring equipment for visual clarity, Asian mean calcium intakes in this study may be more accurate. Additionally, Asian calcium intakes are often reported in combination with other smaller ethnic groups.
The average calcium contribution from milk differed among ethnic groups. Differences were due to differences between white and Hispanic intake, with white intakes higher. But energy contribution from milk was not different among ethnic groups. This may reflect the tendency for Hispanic children and Asian children to choose higher fat milk products than white children.
Milk
Milk products are among the most calcium dense foods. Lactose intolerance can be a barrier to milk consumption among Asians [26]. However, several studies have shown that at least 240 mL of whole or skim milk can be consumed by lactose maldigesters without experiencing adverse symptoms. Additionally, more milk can be consumed without symptoms, if amounts are divided in doses throughout the day [27]. Indeed dairy-rich diets up to 1500 mg/day of calcium can be consumed by lactose maldigesters without significant symptoms [28]. This is important for the Asian population, which has been estimated to have the highest prevalence of maldigestion in the world, close to 100% [29]. This study confirmed the importance of milk as a primary determinant of calcium intake for white, Hispanic and Asian youth. The Committee on Nutrition of the American Academy of Pediatrics does not see primary lactose intolerance as a reason to discourage supplemental milk feeding programs [30].
Added sugars may also displace consumption of milk products and fruits [31]. Data from the present study suggest that soda displaces milk among Hispanic children more than among Asian children. Indeed, association between soda and bone fracture in adolescence has been found [32].
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ACKNOWLEDGMENTS |
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Received June 11, 2002. Accepted August 30, 2002.
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REFERENCES |
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This article has been cited by other articles:
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  S. A. Atkinson, G. P. McCabe, C. M. Weaver, S. A. Abrams, and K. O. O'Brien Are Current Calcium Recommendations for Adolescents Higher than Needed to Achieve Optimal Peak Bone Mass? The Controversy J. Nutr., June 1, 2008; 138(6): 1182 - 1186. [Full Text] [PDF]
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R. Novotny, Y. G. Daida, S. Acharya, J. S. Grove, and T. M. Vogt Dairy Intake Is Associated with Lower Body Fat and Soda Intake with Greater Weight in Adolescent Girls J. Nutr., August 1, 2004; 134(8): 1905 - 1909. [Abstract] [Full Text] [PDF]
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