AWM: High Calcium (2006)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

The purpose of this study was to:

  • further investigate the relation between daily calcium intake and direct measures of body composition
  • test the hypothesis of an association between dietary calcium intake and plasma lipoprotein-lipid concentrations
Inclusion Criteria:
Men and women ages 20-65 years of age who were recruited in phase 2 (1991-1998) of the Quebec Family Study.
Exclusion Criteria:

Participants in the Quebec Family Study sample who regularly used vitamin or mineral supplements

Description of Study Protocol:

Recruitment No information was indicated about specific recruitment procedures used

Design Participants were divided into 3 groups based on their daily calcium intake: groups A (<600 mg), B (600-1000 mg), and C (>1000 mg). After controlling for age, daily energy intake, % body fat, dietary protein, and markers of socioeconomic status and after classifying participants according to daily calcium intake, comparisons were made for men and for women on the following: anthropometric measurements and lipoprotein-lipid concentrations.  

Blinding used (if applicable) NA

Intervention (if applicable) NA

Statistical Analysis Values for men and women were analyzed separately. Pearson's correlations were calculated between daily calcium intake and all body composition variables after taking into account effects of age, daily energy intake, % body fat, dietary protein, and socioeconomic status (total income and highest academic level). Correlations also were performed with residual scores between daily calcium intake and plasma lipoprotein-lipid concentrations after controlling for fat mass and waist circumference.

A 1-way ANOVA was conducted to test for differences in body weight, BMI, fat mass, fat-free mass, % body fat, waist circumference, and abdominal adipose tissue between groups with different calcium intakes. A 1-way analysis of covariance was performed to control for a series of covariates (age, daily energy intake, % body fat, dietary protein, and socioeconomic status) which can impact energy balance and body weight control. A 1-way ANOVA and analysis of covariance were used to compare plasma lipoprotein-lipid profile across subgroups of daily calcium intake with fat mass and waist circumference as covariates. A Tukey's test was then used to assess specific between-group differences when statistical differences were detected.

 

Data Collection Summary:

Timing of Measurements All measurements were obtained during phase 2 of the Quebec Family Study

Dependent Variables

  • Anthropometric measurements: (a) body weight (kg)-measured with a standard beam scale; (b) BMI (kg/meters squared); (c) waist circumference (cm)-measured according to

    Lohman et al.; (d) percentage body fat (%)-measured using the Siri formula; (e) fat mass mass (kg)calculated from the derived % body fat and total body weight; and (f) fat-free mass (kg)-calculated by subtracting fat mass from body weight. 

  • Abdominal adipose tissue-calculated by delineating area with a graph pen and then computing total adipose tissue surface with an attenuation range of -190 to -30 Hounsfield units
  • Plasma lipids and lipoproteins: (a) HDL cholesterol (mmol/L); (b) LDL cholesterol (mmol/L), (c) Triacylglycerol (mmol/L); (d) Total cholesterol (mmol/L); and (e) Total HDL cholesterol. Serum blood lipids were determined using blood samples collected at 0800 after participants had fasted overnight for 12 hours. Total cholesterol and triacylglycerol concentrations were determined enzymatically using commercial kits. HDL-cholesterol and LDL-cholesterol concentrations were analyzed after precipitation of LDL in the infranatant fluid with heparin and magnesium chloride. Ratio of total cholesterol to HDL cholesterol was derived as a lipid index of ischemic heart disease risk.etc

Independent Variables Daily Calcium Intake (Daily energy, macronutrient, and micronutrient intakes)-determined using 3-day dietary records with contents of diet calculated with the Canadian Nutrient File.  For some analyses participants were divided into 3 groups on basis of daily calcium intake: group A has < 600 mg, group B had 600-1000 mg, and group C had intakes of >1000 mg calcium/day.

Control Variables Age, daily energy nitake, % body fat, dietary protein, and markers of socioeconomic status

 

Description of Actual Data Sample:

Initial N: 470 (235 males, 235 females)

Attrition (final N): 470 (235 males, 235 females)

Age: Participants ranged from 20-65 years of age. Women were a mean of 43.5+1.6, 38.8+1.2, and 36.7+1.5 years for Groups A, B, and C, respectively. Men were a mean of 45.3+2.0, 43.2+1.4, and 37.9+1.3 years for Groups A, B, and C, respectively.

Ethnicity: Not indicated

Location: Not indicated specifically, other than this being a Quebec Family Study dataset 

 

 

Summary of Results:
  1. After adjusting for control variables, women who consumed <600 mg dietary calcium/day had significantly greater values than those with daily calcium intakes (P<0.05) for the following: body weight (82.3+3.3 vs. 69.8+1.9 and 65.0+2.7), BMI (31.8+1.2 vs. 27.0+0.7 and 25.2+1.0), % body fat (37.3+1.6 vs. 31.3+0.9 and 28.9+1.2), fat mass (32.4+2.5 vs. 23.6+1.4 and 19.8+1.9), waist circumference (93.6+2.6 vs. 82.0+1.6 and 78.4+2.2), and abdominal adipose tissue (552.2+40.8 vs. 405.7+24.4 and 373.3+33.7).  No significant differences were found across subgroups of men.
  2. Women in group A had a significantly greater ratio of total to HDL cholesterol (P<0.05) than did group C (4.16+0.14 vs. 3.69+0.11);no other significant between-group differences were observed for other lipid-lipoprotein concentrations in women.  No significant differences in plasma lipoprotein-lipid concentrations were found between subgroups among men.
  3. Daily calcium intakes were 861.8+22.8 and 1016.4+30.3 mg/day in women and men, respectively (P<0.01). Most dietary calcium was obtained from dairy products.  
  4. After correcting for confounding variables, significant correlations between daily calcium intake and body-composition variables persisted only in women. Daily calcium intake in women was significantly and inversely correlated with % body fat (r=-0.19, P<0.01), fat mass (r=-0.17, P<0.05), BMI (r=-0.07, P<0.05), and waist circumference (r=-0.07, P<0.05).
  5. After correcting for confounding variables, significant correlations between daily calcium intake and plasma lipoprotein-lipid concentrations were found in women and in men. In women, daily calcium intake was significantly and inversely correlated with LDL cholesterol (r=-0.18, P<0.01), total cholesterol (r=-0.16, P<0.05), and ratio of total to HDL cholesterol (r=-0.15, P<0.05). In men, daily calcium intake was significantly and inversely correlated with LDK cholesterol (r=-0.26, P<0.01), total cholesterol (r=-0.26, P<0.01), and ratio of total to HDL cholesterol (r=-0.15, P,0.05).   

 

 

Author Conclusion:
  1. Results were consistent with other recent studies, indicating a potential effect of calcium on body weight and fat mass in humans.
  2. An interesting finding was that the significant relationships with dietary calcium were observed mainly in women. Body weight, BMI, % body fat, fat mass, waist circumference, and abdominal adipose tissue were all significantly greater in women reported a low calcium intake (<600 mg/day).
  3. This study also indicated a difference in the lipoprotein-lipid profile by dietary calcium intake, independently of adiposity. In males and females, LDL cholesterol, total cholesterol, and ratio of total to HDL cholesterol were all inversely correlated with daily calcium intake.
  4. Dietary calcium was provided predominantly by dairy products in both men and women. This potential effect of calcium on body fatness and lipid metabolism appears to be independent of the macronutrient content (e.g., protein, fat) of dairy products.   
Funding Source:
Government: CIHR
University/Hospital: Laval University, University of Ottawa, Louisiana State University
Reviewer Comments:
No information was provided about race or ethnicity.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? ???
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? N/A
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? No
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) No
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? ???
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes