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Food Sources of Calcium / 199
InternationalJournalofSportNutritionandExerciseMetabolism,2001,11,199-208
© 2001 Human Kinetics Publishers, Inc.
FoodSourcesofCalciuminaSample
ofAfrican-AmericanandEuro-American
CollegiateAthletes
DeborahLeachmanSlawson,BarbaraS.McClanahan,
LindaH.Clemens,KennethD.Ward,RobertC.Klesges,
ChristopherM.Vukadinovich,andEdwinD.Cantler
Adequate calcium intake is integral to bone health as well as for optimal athletic
performance. This study was conducted to investigate: (a) food sources of calcium
in a sample of collegiate athletes, (b) gender and/or ethnic differences in food
sources of calcium, and (c) whether athletes that derive less of their calcium intake
from dairy sources increase their calcium intake from supplements or other food
sources. Participants were African-American and Euro-American NCAA Division 1-A athletes. Eighty-five men and 59 women participated. Calcium intake
for the previous 7-day period was assessed with a brief calcium screen.
Men consumed significantly more calcium than women (1,354 vs. 898 mg/
day), with female cross-country runners exhibiting the lowest average intake
(605 mg/day). Both men and women obtained the majority of their calcium
from dairy products and mixed dishes, while men consumed significantly more
calcium-fortified foods. Several gender and ethnic interactions for calcium intake
from food groups were found. Mean total dairy calcium intake was found to
vary according to total calcium intake in men, and supplemental calcium was
not used to augment low dairy intakes of calcium in any group.
While African-Americans and Euro-Americans athletes were consuming
similar levels of calcium, the female athletes in the sample did not get adequate
amounts.
Key Words: nutrition, sports, diet, race, gender
Adequate calcium intake is necessary for general health and well being, as well as for
optimal athletic performance. To date, no ergogenic qualities have been attributed to
calcium supplementation, but it is clear that inadequate intake may impair skeletal
integrity, nerve impulse transmission, maintenance of membrane potential, and
muscle contraction (7). In an early study, Drinkwater et al. (8) found that too little
D. Leachman Slawson, B.S. McClanahan, K.D. Ward, R.C. Klesges, and C.M. Vukadinovich are with The Center for Community Health at the University of Memphis, Memphis,
TN 38152. L.H. Clemens is with the Department of Consumer Science and Education at the
University of Memphis. E.D. Cantler is with the Department of Intercollegiate Athletics at
the University of Memphis.
199
200 / LeachmanSlawsonetal.
calcium in the diet could be a major contributor to bone loss in otherwise healthy
female athletes. The severity of conditions associated with compromised skeletal
health and inadequate calcium intake heighten the need to identify groups that may
be at increased risk for the potential adverse consequences of inadequate calcium
intake. Athletes, particularly women in weight-conscious sports, appear to be such
a group.
In spite of increased physiologic demands that may lead to additional pathways
for calcium loss, there is evidence that athletes consume less than the current Daily
Reference Intake (DRI) for calcium (1, 7, 16, 27). The DRI for 19–30 year-olds is
1,000 mg/day (11). Further, the NIH Consensus Conference on Optimal Calcium
Intake has recommended the intakes for adolescents and young adults be set at 1,500
mg/day (29). At particular risk for low calcium intake are those athletes who strive
to achieve low body fat, those who are involved in excessive training programs, and
those who have inadequate energy intake (10). Additionally, it appears that calcium
intake may be related to stress fracture risk. For example, Myburgh et al. (28) found
that athletes with confirmed stress fractures had lower calcium intakes than did
activity-matched athletes with no history of fractures. In addition, those with stress
fractures reported a history of low intakes of dairy products, suggesting that calcium
intake may influence the incidence of stress fractures in athletes (28).
These findings point to the need to investigate the adequacy of calcium intakes
in certain athletes who may be at increased risk of inadequate intake. For example,
many female athletes have been shown to consume less than the Recommended
Dietary Allowance of calcium (7). Low calcium intake in young adulthood is of
particular concern given that this stage in the lifespan is one of the prime times for
optimizing bone density, and women, particularly Euro-American women, are at
greater risk for developing osteoporosis in later years (5).
While osteoporosis is less common in African-Americans (23), several investigators have related low calcium intakes with the development of hypertension (12,
19, 21, 25), a potentially life-threatening condition prevalent in the older AfricanAmerican population (20). Eck and Hackett-Renner (9) found that African-American
children and adolescents consistently consumed less calcium than did Euro-American
children and adolescents. Similarly, Looker et al. (22) found that, in the general U.S.
population, African-Americans of both genders had the lowest calcium intake of
several ethnic groups. Given that dairy foods are a primary source of calcium for this
ethnic group (3, 22), the prevalence of lactose intolerance in African-Americans (31)
may have a large negative effect on calcium intake in this population.
Further, while the majority of calcium intake for both ethnic groups is derived from dairy foods (3, 22), the perception of dairy products as being high in fat
may influence their intake (17). This possibility is illustrated in an investigation of
changes in calcium intake in youth, where girls of both ethnic groups, aged 13–18
years old, consumed almost 200 mg/day less calcium than girls 6–7 years old (9).
Additionally, calcium intake in that study steadily decreased as age increased, with
the most dramatic decrease seen between the ages of 11–12 and 13–18.
Given that calcium intake plays an integral role in multiple physiologic responses to increased physical workloads, and is necessary for the optimization of
long-term health outcomes, the purpose of this study was three-fold: (a) to add to
the existing body of literature by documenting calcium intake in athletes involved
in sports with differing physiologic requirements; (b) to examine ethnic and gender
variations in dietary sources of calcium in athletes; and (c) to examine issues of dietary
Food Sources of Calcium / 201
compensation and supplementation in athletes with low intakes of dairy foods.
Methods
Participants were 145 collegiate athletes (86 males and 59 females) representing five
menʼs teams (basketball, football, golf, soccer, track/cross-country) and five womenʼs
teams (basketball, golf, tennis, track/cross-country, volleyball). All participants were
volunteers and were not financially compensated for their participation. The average
age for female participants was 19.6 years (range: 18–23), and for males, 20.3 years
(range: 18–24). These team selections represent a spectrum of physiologic requirements in relation to differences in exertion, sweat loss, and weight-bearing skeletal
impact. Overall, males represented 59.3% of the sample. Of the male athletes, 66%
were Euro-American and 34% African-American. Of the female athletes, 63% were
Euro-American, and 37% were African-American.
A calcium checklist developed by Hertzler and Frary (13) was used to assess
calcium intake. This measure was developed for use with adolescents and has been
shown to compare well to food recalls and records (13). For this study, this measure
was used in its entirety and included three additional items that were used to query
the intake of locally available foods fortified with calcium (orange juice, bread, light
bread). Using food models to demonstrate serving sizes, a member of the research team
administered all assessments. Participants were asked to report the number of times
each food had been consumed over the previous 7 days. All measures were checked
Table 1
Foods/Beverages Included on the Calcium Checklist
Mixed dishes:
cream soups/sauces; macaroni and cheese; pizza or quiche;
Milk, yogurt:
cheese, cottage cheese; milk or cocoa; soy milk; yogurt;
Dairy desserts:
custard, pudding, cream pie; ice cream, frozen yogurt, milk shake;
Fruits and
vegetables:
broccoli or cooked greens (beet/turnip greens, kale, collards,
spinach); other vegetables; fruits;
Grains:
bread or cereal; biscuit/roll, or corn tortilla; muffin, cornbread, or
doughnut; rice, noodles, or pasta; pancake, waffle, or French toast;
Calcium-fortified
foods:
orange juice with calcium added, bread with calcium added; light
bread with calcium added;
Protein foods:
dried beans, cooked (navy, pinto, kidney); meat, fish, poultry;
peanuts, egg; salmon with bones or sardines with bones; shrimp or
oysters; tofu;
Miscellaneous:
cake; beer; colas; chocolate;
Supplements:
Subjects were asked if they had taken any vitamin/mineral supplements in the past 7 days. If they responded affirmatively, they were
asked to list the type of supplement and how many they had taken in
the 7 days covered.
Note. Subjects were instructed to report how many times they had consumed each
item in the previous 7 days.
202 / LeachmanSlawsonetal.
for completeness before each participant left the laboratory. Foods on the checklist
were then collapsed into the following categories: mixed dishes, milk/yogurt, dairy
desserts, fruits/vegetables, grains, calcium-fortified foods, protein foods, miscellaneous foods, and supplements. Table 1 provides a list of foods in each grouping.
Results
TeamEffects
Table 2 presents average daily calcium intakes by gender and sports team, with the
percent of participants by team reporting calcium intakes less than two thirds of the
Daily Reference Intake (DRI) of 1,000 mg/day.
Supplemental calcium also is included in the mean calcium intakes listed.
Female cross-country runners consumed the least calcium, with an average of 605
mg/day, and the majority of these athletes reported calcium intakes less than two
thirds of the DRI. Conversely, male basketball players consumed the most calcium,
with a mean of 1,730 mg/day, with none of these athletes reporting calcium intakes
Table 2 Mean Daily Calcium Intakes by Gender and Sport, With Percent of
Participants Reporting Calcium Intakes Less Than Two Thirds of DRIa
(N = 145)
Variable
Men
Basketball
Football
Golf
Soccer
Cross-country
Indoor/outdoor track
Subtotals for men:
Women
Basketball
Golf
Tennis
Cross-country
Indoor/outdoor track
Volleyball
Subtotals for women:
n
% of total
sample
Mean calcium
intake (mg/day)b
Percent below
two thirds DRI
10
24
11
21
7
13
86
6.9
16.5
7.6
14.5
4.8
9.0
59.3
1730
1335
784
1367
1706
1369
1354
±
±
±
±
±
±
±
867c
1003
292
560
1153d
1248
904e
0
16.7
45.4
4.8
14.3
15.4
15.1
13
7
6
12
12
9
59
9.0
4.8
4.1
8.3
8.3
6.2
40.7
1101
1052
849
605
974
804
898
±
±
±
±
±
±
±
934
604
215
182
459
321
467
23.1
42.9
16.7
66.7
25.0
44.4
37.3
a
Two-thirds of the Daily Reference Intake of 1,000 mg/day is 670 mg/day.
Mean ± SD.
c
Significant difference between menʼs basketball and womenʼs cross-country (p = .022).
d
Comparison of menʼs and womenʼs cross-country teams (p = .083).
e
Significant difference between men and women overall (p = .0037).
b
Food Sources of Calcium / 203
below two thirds of the DRI. With the exception of the male golf team, calcium intakes
of women on all teams were lower than those of the male teams. While the overall
mean for male athletesʼ calcium intakes exceeded the DRI, 15% (one in seven) did
not consume at least two thirds of the DRI. Further, one in three of the female athletes
did not consume at least two thirds of the DRI. Team effects were investigated via an
analysis of variance (ANOVA). The overall model was significant (F11,133 = 2.444,
p = .008 with Tukey Honestly Significant Difference follow-up tests indicating a
significant difference between womenʼs cross-country and menʼs basketball (p =
.022), and a marginally significant difference between womenʼs and menʼs crosscountry teams (p = .083).
SexandEthnicEffectsinSourcesofCalciumIntake
Sex and ethnic differences in calcium intake were examined using 2-way ANOVA,
with sex (male, female) and ethnicity (African-American, Euro-American) as main
factors. Significant main effects and interactions were followed up using Tukeyʼs
Honestly Significant Difference tests. Table 3 shows average daily calcium intake
from each food group, reported for the previous 7-day period according to gender
and ethnicity. Values are presented as mg/day, representing the mean for the 7-day
period. There were no significant differences in total calcium intakes by race, though
males had significantly higher intakes of total calcium than did females (1,354 vs. 898
mg/day, F1,141 = 8.73, p = .0037). When categories of calcium intake were examined
separately, significant sex effects were observed for three categories, with males
having higher intakes than females for mixed dishes (359 vs. 239 mg/day, F1,141 =
4.33, p = .04), calcium-fortified foods (220 vs. 130 mg/day, F1,141 = 3.70, p = .056)
and protein foods (38 vs. 21 mg/day, F1,141 = 12.56, p = .0005).
Sex by race interactions were observed for the milk/yogurt group (F1,141 =
Table 3
Calcium Intake (mg/day) by Gender and Race (Mean ± SD)
Men
Variable
EuroAmerican
n = 57
AfricanAmerican
(n = 29)
Women
EuroAfricanAmerican
American
(n = 37)
(n = 22)
Mixed dishes
Milk/yogurt
Dairy desserts
Fruit/vegetables
Grains
Calcium-fortified foods
Protein foods
Miscellaneous
Supplements
402
506
74
67
108
206
34
41
34
273
255
56
91
102
248
51
35
9
225
195
75
82
79
135
16
33
37
±
±
±
±
±
±
±
±
±
287
592
84
56
86
292
29
31
127
Total dairy
984 ± 740
Total mean calcium/day 1,472 ± 962
±
±
±
±
±
±
±
±
±
274
306
63
81
74
454
53
44
34
584 ± 487
1,120 ± 740
±
±
±
±
±
±
±
±
±
224
165
91
68
48
158
14
39
76
496 ± 325
878 ± 434
262
255
89
46
91
122
28
31
8
±
±
±
±
±
±
±
±
±
201
330
83
30
74
129
28
31
25
605 ± 489
930 ± 527
204 / LeachmanSlawsonetal.
Figure 1 — Proportional intake of calcium from each food grouping by ethnicity:
men.
Figure 2 — Proportional intake of calcium from each food grouping by ethnicity:
women.
4.32, p = .04), fruits/vegetables (F1,141 = 7.49, p = .007, and total dairy (F1,141 = 6.36,
p = .013). Follow-up testing indicated that for milk/yogurt, Euro-American males
had significantly higher intakes than did Euro-American females (p < .05). Looking
at fruit/vegetable intake, African-American males had significantly higher intakes
than African-American females. Finally, and perhaps most interestingly, a followup 1-way ANOVA revealed that, for total dairy intake, Euro-American males had
significantly higher intakes than any other group (for all, p < .05). Figures 1 and 2
present an illustration of the proportional intake from each food grouping for each
racial group for men and women, respectively.
AnalysisofPotentialCompensationforLowDairyFoodIntake
To investigate whether individuals compensated for low calcium intake from dairy
foods by increasing intake from non-dairy calcium sources, participants were grouped
by gender, and classified into tertiles of low, medium, and high dairy calcium intake.
As body weight was associated with both total calcium intake (r = 0.311, p < .001)
and calcium intake from dairy sources (r = 0.270, p = .001), an analysis of covariance
(ANCOVA) was carried out for each tertiled gender group using body weight as a
covariate. For men, there was a marginally significant, positive linear trend, such that
greater dairy calcium intake was associated with greater non-dairy calcium intake
Food Sources of Calcium / 205
(F2,82 = 2.680, p = .075). There were no significant trends noted for the women (F2,55
= 0.303, p = .740). Thus, there was little evidence that individuals with low dairy
calcium intake compensated by increasing intake from other food groups. The same
pattern of results emerged when subjects were excluded who were statistical outliers
(≥3 SDs above the mean) on dairy calcium intake (n = 4).
Further, subject groupings by tertile of dairy calcium intake were examined to
determine whether individuals with low dairy calcium intake, compared to individuals
with higher intake, were more likely to have used oral calcium supplements in the
previous week. Among the three tertiles of dairy calcium intake, the percentage of
subjects using oral supplements ranged from 12.5–16.0%, with daily doses ranging
from 23–771 mg. These differences were not statistically significant [C2(2) = 0.25,
p = 0.88]. Similarly, oral supplement use was not related to dairy calcium intake when
the lowest two tertiles were combined and compared to the highest tertile [C2(2) =
0.23, p = .63]. Thus, subjects with a low intake of calcium from dairy sources did not
compensate by taking calcium supplements.
Discussion
Similar to earlier reports in non-athletes (5), the men in the present investigation
consumed more calcium than did the women. Average daily means were 1,354 and
898 mg for men and women, respectively; and while menʼs average intake exceeded
the DRI, one out of seven failed to consume two thirds of the DRI. The women, on
average, consumed slightly below the DRI of 1,000 mg/day, and a full 37% consumed
less than two thirds of the DRI. Concerning sources of calcium intake, men consumed
significantly more calcium from mixed foods, calcium-fortified foods, and protein
foods. Overall, men tended to obtain the majority of their calcium from dairy products (848 mg), mixed dishes (359 mg), and calcium-fortified foods (220 mg). While
women also consumed the majority of their calcium via dairy products (536 mg) and
mixed dishes (238 mg), their total intake of calcium remained below the DRI.
The observed low calcium intakes in female athletes are in agreement with
previous reports of low calcium intake in both athletic women (1, 7, 16, 27) and
non-athletic women (15). Such findings are particularly troubling, since there are
more pathways for calcium loss in athletes, and given the recommendations of the
NIH Consensus Conference on Optimal Calcium Intake (29), which suggest optimal
calcium intakes for adolescents and young adults as 1,500 mg/day, a level that is 500
mg greater than the DRI. This group of women consumed roughly 60% of the level
recommended by the NIH, suggesting that these female athletes may be at increased
risk for compromised skeletal integrity. This finding is even more alarming for those
athletes who seem to be most prone to low calcium intake and, subsequently, lowered
bone density (1, 7, 16, 27). Of particular concern are those athletes who frequently
participate in long endurance, impact-loading activities such as jogging. Frequent
participation in such activities has been associated with compromised bone health
by several investigators (2, 4, 14, 24, 26). The female cross-country runners in this
sample averaged the lowest calcium intake of all teams (605 mg/day) and thus may
be at increased risk for low bone density.
Although both Euro-American and African-American men consumed more
than the DRI at a mean intake of 1,476 mg/day and 1,120 mg/day, respectively, 15.1%
(one in seven) of the male athletes reported calcium intakes less than two thirds of
the DRI. This level of intake may be inadequate to prevent exercise-related bone loss
206 / LeachmanSlawsonetal.
(28). Similarly, preliminary research in our laboratory found evidence of exerciserelated bone mineral loss among male basketball players that was more pronounced
at calcium intakes of less than 2,000 mg/day (18). Therefore, it is plausible that the
DRI, which is designed to address the needs of most Americans, may not represent
an adequate goal for athletes. Interestingly, while the Klesges et al. (18) investigation was conducted under conditions that would promote increased dermal losses
of calcium through perspiration, the observed bone loss was subsequently reversed
by supervised calcium supplementation. Given that the male athletes in the current
investigation were consuming calcium at levels much lower than 2,000 mg per day
and did not use supplementation to augment their calcium intakes, it is possible that
these athletes might be losing bone mass.
While no specific U.S. standards currently exist for athletes for calcium intake,
this study underscores the need to investigate athletesʼ requirements as they relate to
differing physiologic requirements of sport-specific activities. Increased pathways
for calcium loss associated with athletic participation suggest that calcium intake
and possibly calcium supplementation should be important considerations for all
athletes. However, athletes typically take part in nutrient supplementation in hopes of
improving athletic performance (30). To date, calcium supplementation has not been
associated with any ergogenic qualities, and many athletes may fail to understand the
long-term consequences of inadequate calcium intake. Thus, it is important to educate
athletes about the importance of adequate calcium intake in order to promote skeletal
integrity and possibly to reduce the risk of stress fractures. Further, investigations
should be pursued to determine which athletes may be at greatest risk for bone loss,
and at what level supplementation may mediate that loss.
Contrary to other investigations (9, 22), African-Americans and Euro-Americans in this sample were consuming a similar level of calcium. There were several
gender and ethnic differences in sources of intake. African-American men consumed
more calcium from the fruit/vegetable group than did African-American women.
Euro-American men were consuming more calcium from the milk/yogurt group than
were any of the other three groups. This finding may indicate that the young women
in this sample avoided dairy products as a way of controlling total energy and fat
intake, as has been observed in other studies (9, 17).
When the sample was stratified based on total dairy calcium intake, there was
no relationship between total dairy calcium intake and non-dairy calcium intake for
women, and the relationship was only marginally significant for men. Thus, athletes
did not compensate for low intakes of calcium from dairy foods by consuming food
from other groups. Athletes from the three tertiles of total dairy calcium intake did
not differ in their use of calcium supplements, indicating that athletes who consumed
a relatively low amount of dairy products did not attempt to compensate either from
non-dairy calcium sources or from calcium supplements.
Although this study provides information on the food sources of calcium and
compensation for low intake from dairy foods, several design issues limit the study.
First, we elected to study only calcium intake. Although it is clear that other nutrients
are important in bone health, we felt that calcium intake held the most promise for
developing educational strategies to positively impact bone health. That is, other
nutrients (e.g., phosphorus) are important but may be less amenable to education
efforts. Furthermore, calcium content of foods is easy to understand and is probably
more salient to this age group. Other issues, such as the absorption rate of calcium
and bone mineral density, also were not evaluated in this study. Such information
Food Sources of Calcium / 207
would require more extensive laboratory analyses and was not the focus of this study.
Lastly, our sample was limited to NCAA Division 1-A athletes at the university level,
and further work is needed to determine how well these results generalize to athletes
at other competitive levels and other ages.
In summary, it appears that college-age female athletes are not getting adequate
calcium. Further, while college-age male athletes are generally surpassing the DRI
for calcium, one in seven were consuming calcium at levels less than two thirds of
the DRI. Neither male nor female athletes reached the level of calcium intake recommended by the NIH Consensus Conference (29). Furthermore, African-American
athletes were consuming a level of calcium similar to that of the Euro-American
athletes. Finally, athletes with low levels of intake from dairy foods do not appear to
be compensating by consuming calcium from other food sources or supplements.
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