Maturitas 69 (2011) 168–172
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Validation of a calcium assessment tool in postmenopausal Canadian women
Ada Hunga,b, Maryam Hamidia,b, Ekaterina Riazantsevaa, Lilian Thompsonc, Lianne Tilea,d,
George Tomlinsond,f, Brooke Stewarta, Angela M. Cheunga,b,d,e,f,∗
aOsteoporosis and Women’s Health Programs, University Health Network, Toronto General Hospital, Toronto, Canada
bInstitute of Medical Science, University of Toronto, Toronto, Canada
cDepartment of Nutritional Sciences, University of Toronto, Toronto, Canada
dDivision of General Internal Medicine, University of Toronto, Toronto, Canada
eDivision of Endocrinology, Department of Medicine, University of Toronto, Toronto, Canada
fClinical Epidemiology Program, Department of Health Policy, Management and Evaluation, University of Toronto, Toronto, Canada
a r t i c l ei n f o
Received 3 August 2010
Received in revised form 18 February 2011
Accepted 28 February 2011
Dietary assessment tool
a b s t r a c t
is neither widely done nor standardized in North American clinical practices.
Objective: Our goal was to validate a calcium assessment tool (CAT), a modified version of the Calcium
CalculatorTM, against the 3-day food record.
Methods: Data were obtained from 348 participants in the ECKO (Evaluation of the Clinical use of vita-
min K supplementation in postmenopausal women with Osteopenia) trial. In this study, CAT data was
collected at baseline and 3-day food records (FRs) were collected at baseline and 3 months by trained
study coordinators. CAT and 3-day FR data were compared using correlations and Bland–Altman plots.
Additionally, receiver operator characteristic (ROC) curves of CAT were constructed to identify subjects
with low calcium intake at thresholds of 500mg/day and 1000mg/day on the 3-day FR curves.
Results: Mean calcium intake values per day were 902mg for the 3-day FRs and 781mg for the CAT. The
Pearson correlation was 0.57 (95% CI: 0.50–0.64). Areas under the ROC curves at thresholds of 500 and
1000mg calcium were 0.81 (95% CI: 0.73–0.89) and 0.82 (95% CI: 0.78–0.86), respectively.
Conclusions: The CAT is a valid tool for the measurement of dietary calcium intake using cut-off values of
the CAT and 3-day FR. This tool may facilitate the determination of whether calcium supplements are
needed in the clinical setting.
© 2011 Elsevier Ireland Ltd. All rights reserved.
Calcium is an essential nutrient in maintaining optimal health.
It is a structural element in the bone and also involved in nerve
Abbreviations: CAT, calcium assessment tool; ECKO„ Evaluation of the Clini-
cal use of vitamin K supplementation in postmenopausal women with Osteopenia;
ROC, receiver operator characteristic; FR, food record; CI, confidence intervals; RDA,
recommended daily allowance; BMD, bone mineral density; FFQ, food frequency
questionnaires; AUROC, area under the ROC curve; ICC, intra-class correlation coef-
∗Corresponding author at: 200 Elizabeth Street, 7 Eaton North – 221, Toronto,
Ontario, M5G 2C4, Canada. Tel.: +1 416 340 4301; fax: +1 416 340 4105.
E-mail addresses: firstname.lastname@example.org (A. Hung),
email@example.com (M. Hamidi), Ekaterina.Riazantseva@uhn.on.ca
(E. Riazantseva), Thompson@utoronto.ca (L. Thompson), firstname.lastname@example.org
(L. Tile), email@example.com (G. Tomlinson), firstname.lastname@example.org
(B. Stewart), email@example.com (A.M. Cheung).
conduction, muscle contraction and blood clotting and therefore,
from the skeleton, leaving the bones less dense and more frag-
ile over time. In combination with vitamin D, adequate calcium
intake through diet and supplementation has been shown in ran-
maintaining BMD [1,2], decreasing fractures [3,4], and even reduc-
ing colorectal cancers and gynaecologic cancers [5,6]. On the other
hand very high intakes of calcium may lead to an increased risk of
kidney stone formation , myocardial infarctions , hypercal-
cemia , and decreased absorption of other essential minerals.
The Recommended Dietary Allowance (RDA) for calcium are
1000mg/day for adults 19–50 years of age and 1200mg/day for
adults aged ≥51 and the tolerable upper intake level is set at
under age 51 meet the RDA levels, older women may be at risk of
0378-5122/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved.
A. Hung et al. / Maturitas 69 (2011) 168–172
calcium is needed to maintain health without causing adverse
calcium intake through diet and supplements. Assessing dietary
calcium intake, however, is neither widely done nor standardized
in North American clinical practices.
The food record (FR) is the gold standard for assessing calcium
tise in the use of nutrition analysis software as well as subject
training. By contrast, food frequency questionnaires (FFQ) are a
more practical and efficient means of collecting dietary data in the
of calcium intake in different countries [11–20] yet, these studies
also identified a need to validate FFQs in each region of use, due to
cultural and geographic variations.
There are currently no published studies using a validated
by registered dietitians working for the BC Dairy Foundation in the
1980s . The objective of our study was to assess the validity of
a modified FFQ from the Calcium CalculatorTM, called the Calcium
Assessment Tool (CAT), by examining its agreement with the 3-day
FR method among Canadian postmenopausal women.
2. Materials and methods
2.1. Study population and design
The subjects for this validation study were postmenopausal
Canadian women participating in an osteoporosis prevention trial
(ECKO—Evaluation of the Clinical use of vitamin K supplementa-
tion in postmenopausal women with Osteopenia) at the University
Health Network (UHN), University of Toronto . Women were
recruited through health fairs, advertisements and posters from
January 2002 to September 2004 in the Greater Toronto Area.
Women were included if they were postmenopausal (at least 1
year after their last menses) and had their lowest BMD T-score
(total lumbar spine L1–L4, total hip or femoral neck) between
−1.0 and −2.0. Women were excluded if they had osteoporo-
sis, fragility fracture after the age of 40, bone medication use in
the past 3 months (bisphosphonates, selective estrogen receptor
modulators, hormone replacement therapy or calcitonin); any bis-
phosphonate use for more than 6 months; known metabolic bone
diseases or diseases of the liver, kidney, pancreas, lung or heart;
history of active cancer in the past 5 years; or chronic oral steroid
or E (>400IU/day). All women gave informed consent prior to the
start of study procedures and the protocol was approved by the
UHN and University of Toronto research ethics boards.
2.2. Dietary calcium assessment
2.2.1. Dietary calcium assessment using CAT
Participants were interviewed by trained study coordinators at
on a short FFQ developed by the BC Dairy Foundation, as part of
their 2002 brochure version of the Calcium CalculatorTMwhich
is an interactive educational tool [21,23,24]. This FFQ contains 26
items that are most abundant in calcium and commonly eaten in
British Columbia (Sydney Massey, personal communication). Por-
tion sizes are given in common household measurements such as
slices, cups, tablespoons, cube size and cans. Each portion size con-
tains at least 50mg of calcium, with increments of 75, 150, 250
and 300mg per portion. The 2002 brochure version of the BC Dairy
Foundation Calcium CalculatorTMasked individuals what they ate
the day before. In our study, we asked individuals what they had
consumed in the past 7 days to obtain an average daily intake. Use
of calcium supplements was asked separately afterwards. The total
amount of calcium (in mg) was divided by 7 to find the average
intake per day.
2.2.2. Dietary calcium assessment using 3-day food records
consecutive days (two weekdays and one weekend) in two time
periods; once immediately after the baseline visit and again the
week prior to the 3-month visit. Subjects recorded the descrip-
tion, time, portion sizes (using common household measurements
such as cups, slices and tablespoons) and recipes of the foods
eaten. A portion size guide, developed by the Fred Hutchinson
Cancer Research Center , was used in this study. Completed
and returned FRs were entered by trained research assistants into
the Food Processor software from Elizabeth Stewart Hands and
2.3. Statistical methods
and 3-month 3-day FRs was assessed using the intra-class correla-
tion coefficient (ICC)  (estimated from one-way random effects
means. The Bland–Altman method  was used to assess agree-
ment of calcium intake as measured by the FR and CAT. Using this
method, we estimated the difference in the mean calcium intake
on the two calcium intake values calculated for any one individual.
We also computed the Pearson correlation between the calcium
intake on the FR above and below two important thresholds :
below 500mg/day and below 1000mg/day on the FR. These two
thresholds were chosen based on the distributions of dietary cal-
cium consumption in the population , along with RDA levels.
CAT values for classifying calcium intake as high or low. The area
under the ROC curve (AUROC) and its confidence intervals were
calculated by using the equivalence to the Mann–Whitney statis-
tic. Boxplots were used to present the distributions of CAT values
for subjects above and below the thresholds on the 3-day FR.
Out of 440 postmenopausal women in the ECKO trial, 52 had
either incomplete CATs or 3-day FRs or both at baseline. At 3
months, 36 women had missing and 4 had incomplete 3-day FRs.
day FRs are included in this study. The demographic characteristics
of the 348 subjects are shown in Table 1.
The ICC between the baseline and 3-day FRs was 0.61 and
the difference in mean calcium intake on the two occasions was
60mg/day. Calcium intake from the 3-day FRs ranged from 135
to 2398mg/day, with a mean of 902mg/day. Calcium intake, as
calculated by the CAT, ranged from 50 to 2486mg/day, with a
mean of 781mg of calcium per day. There was a moderate corre-
lation between the 3-day FRs and CAT (r=0.57, 95% CI: 0.50–0.64)
(Figs. 1 and 2) but the CAT on average underestimates the total cal-
calcium per day. The estimated 95% limits of agreement for values
computed on the same person by the two techniques were −600
to 841mg of calcium per day. When we examined the performance
A. Hung et al. / Maturitas 69 (2011) 168–172
Demographic characteristics of 348 postmenopausal women who completed 3 day
food records at baseline and three months follow-up, along with a CAT.
Age at Menarche (range)
Age of menopause
Natural menopause (range)
Surgical menopause (range)
Years since menopause (SD)
BMI (kg/cm2) (SD)
Ethnicity (number and proportion)
African Canadian (%)
Education (number and proportion)
High school or less (%)
Community College (%)
Post graduate (%)
Married/common law (%)
Family osteoporosis history (%)
Previous HRT use (%)
Current smoker (%)
Previous smoker (%)
≤1serving /day (%)
≥1serving /day (%)
Bone mineral density (g/cm2)
Spine L1–L4 (SD)
Total hip (SD)
Femoral neck (SD)
Ultra distal radius (SD)
25-Hydroxyvitamin D (nmol/L) (SD)
Discontinued within 1 year (%)
of the CAT for identifying subjects below different thresholds of
calcium intake per day based on the 3-day FR, we found that the
AUROC was 0.81 (95% CI: 0.73–0.89) (Fig. 3a), with a sensitivity of
0.73 (95% CI: 0.56–0.85) and specificity of 0.79 (95% CI: 0.75–0.84)
the threshold of 500mg/day, while 315 were above the threshold.
For the threshold of 1000mg/day, the AUROC was 0.82 (95% CI:
0.78–0.86), with a sensitivity of 0.71 (95% CI: 0.65–0.77) and speci-
ficity of 0.72 (95% CI: 0.63–0.79) (Fig. 3b). 230 and 118 participants
were respectively below and above this threshold.
Fig. 1. Plot of values (mg/day) from 3-day food records (average of baseline and 3
months follow-up) versus the values for CAT, with Pearson correlation of 0.57.
Fig. 2. Bland–Altman plots of values from 3-day food records and CAT.
This is the first large study in Canada to validate a short FFQ to
assess calcium intake for clinical use in postmenopausal women.
Our study showed moderate correlation between the CAT and the
3-day FR. Although, CAT underestimates the 3-day FRs by 121mg
of calcium intake per day, the magnitude of our underestimation
of calcium intake by the CAT falls within the range of underes-
timations found in other calcium FFQ validation studies (range:
6.7–212mg) [11,14–16,18,20,31–33]. The AUROC values show that
below certain thresholds of calcium intake.
Our results are similar to other validation studies between FFQs
and reference methods [11–20]. While most studies showed corre-
lations between 0.49 and 0.79, Khan et al.  and Montomoli et al.
 showed the highest correlations of 0.84 and 0.9, respectively,
likely because their subjects lived in small towns with a cultur-
ally homogenous diet. This is in contrast to the dietary diversity
found in most metropolitan populations. Similar to results in the
Magkos et al. study , the Bland–Altman plot in our study shows
that the differences increase at higher intakes of calcium, which
is expected as variability increases with higher calcium levels. On
the other hand, the higher value of the 3-day FRs can be attributed
to various factors. First, the 3-day FRs have better capture of the
total calcium intake than the CAT which has a limited number of
food items. Second, the analysis software used in this study also
accounted for calcium intake from foods with partial ingredients
from mixed food items, such as sesame seeds from a bagel.
(95% CI: 0.73-0.88)
0.0 0.2 0.4 0.60.8 1.0
(95% CI: 0.77-0.86)
Fig. 3. The receiver operator characteristic curve identifying values above the (a)
500mg/ day and (b) 1000mg/ day thresholds using the CAT.
A. Hung et al. / Maturitas 69 (2011) 168–172
Our study has several strengths. First, the CAT questionnaire
reflects Canada’s multicultural population by including a variety of
naires are typically difficult to adapt from other countries for use
in North America, due to variations in the local diet of the culture.
For example, Khan et al. , showed that small crabs account for
33.8% of the calcium intake of a population in the Red River Delta in
Vietnam, however, dairy products contributed only 0.38%. By con-
trast, dairy products accounted for at least 46% of calcium intake
in Canadian diets . Second, our study contains a large cohort
of 348 postmenopausal women, compared to other North Ameri-
can studies with typically fewer than 100 postmenopausal women
calculate the calcium intake directly onto one record sheet which
FFQs commonly use a separate reference sheet to calculate intake
Our study has several limitations. First, despite the availabil-
ity of multicultural foods in supermarkets and restaurants our
subjects were predominantly Caucasian postmenopausal women
recruited from one geographic region, the Greater Toronto Area.
Second, there are limitations related to our dietary intake instru-
ments. Recall bias may be associated with the CAT, as food intake is
underreporting and simplification, as study participants are faced
with the new and unusual routine of recording every food item
eaten throughout the day. However, despite these potential limita-
FR is a good compromise between reliability, compliance and daily
dietary variability. Finally, even though nutritionists were avail-
able to clarify any unclear dietary items, misinterpretations may
Despite the limitations we have noted, our study shows that the
CAT is a valid tool and can be used to assess dietary calcium intake
and adequacy in postmenopausal women when 3-day FRs are not
possible. When the CAT is used in the clinical setting, clinicians
must be aware that the values obtained may be slightly lower than
the patient’s actual intake.
Dr. Angela Cheung led the study concept, design, acquisition
of data and critical review of the manuscript and had primary
responsibility for final content. Ada Hung actively participated in
data management and was involved in the analysis and interpre-
tation of data, drafting of the manuscript, and critical review of
design of the study, acquired and had full access to all of the data,
sis and critical review of the manuscript. George Tomlinson led the
statistical analysis and was involved in the critical review of the
manuscript. Ekaterina Riazantseva, Lilian Thompson, Lianne Tile,
and Brooke Stewart contributed to data acquisition and critically
reviewed the manuscript.
Cheung has been supported by a 5-year CIHR mid-career award in
We thank all our subjects for participating in this study. We
also thank Lidia Matic for data entry and organization of the food
record data, and Yena Ahn and Zoe Agnidis for their assistance in
preparation of the manuscript for submission.
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