Tami's Folder
To investigate the predictive ability of the BMI categories identified in the WHO Weight Classification System and change in BMI on mortality in Canadian seniors.
- Canadian Study of Health and Aging participants who completed clinical examination in 1991 and 1996 were included
- Participants with height and weight from CSHA1 and CSHA2, as well as information about whether they died between CSHA2 and CSHA3.
- Those who died in the first five years of follow-up
- Those diagnosed with dementia at CSHA2 and were not followed to CSHA3 (N=317)
- Those lost to follow-up between CSHA2 and CSHA3 (N=23).
Recruitment
The Canadian Study of Health and Aging (CSHA) is a national multi-center cohort study of dementia, as well as a longitudinal health study of elderly Canadians. Of the 10,263 individuals 65 years and above surveyed in 1991 and 1992 (CSHA1), 9,008 were living in the community and 1,028 in long-term institutions. The very old were oversampled. 2,914 elderly underwent the clinical examination at CSHA1.
Design
Cohort study.
Statistical Analysis
- Descriptive analyses were completed for covariates included in the analyses
- Bivariate analyses were completed for weight change categories with other covariates
- Logistic regression controlled for age, gender, education level, marital status, smoking and cognitive status
- Odds ratios and 95% confidence intervals were calculated.
Timing of Measurements
CSHA1 occurred in 1991, CSHA2 in 1996 and CSHA3 in 2001.
Dependent Variables
- Five-year mortality (death between CSHA2 and CSHA3)
- Information about vital status was collected from a decedent questionnaire administered to a proxy resident at CSHA3
- Death certificate information was collected for most of the subjects who died.
Independent Variables
- Actual measurements of height (using stadiometer) and weight (using calibrated balance scales) recorded
- BMI change (CSHA1 to CSHA2) was categorized as no change or mild increase (between zero and two units), mild decrease (between -0.1 and -2.0 units) or significant increase or decrease (more than two units either way).
Control Variables
- Age
- Gender
- Education level
- Marital status
- Smoking
- Cognitive status at CSHA2.
- Initial N: 2,914 elderly underwent the clinical examination at CSHA1.
- Attrition (final N): 539 participants included in the analysis,61% were female
- Age
- 65 to 74 years: 30.6%
- 75 to 84 years: 55.8%
- 85 years or older: 13.5%
- Ethnicity: Not mentioned
- Location: Canada.
Adjusted Relative Odds of Death Between 1996 and 2001: Multivariate Models (n = 539)
Variables |
Model I |
Model II |
Model III |
Age 75 to 84 years |
3.46 (2.17, 5.53)
|
3.52 (2.19, 5.68)
|
3.89 (2.28, 6.63)
|
Age 85+ years |
12.3 (6.30, 24.0)
|
11.4 (5.8, 22.3)
|
11.6 (5.3, 25.2)
|
Male |
1.78 (1.21, 2.62)
|
1.91 (1.28, 2.84)
|
1.73 (0.99, 2.98)
|
BMI <18.5 |
1.84 (0.66, 5.18)
|
1.94 (0.68, 5.51)
|
1.95 (0.61, 6.31)
|
BMI, 25-29.9 |
0.74 (0.49, 1.12)
|
0.69 (0.45, 1.05)
|
0.70 (0.44, 1.11)
|
BMI 30+ |
1.01 (0.54, 1.90)
|
0.90 (0.47, 1.70)
|
0.91 (0.45, 1.86)
|
BMI Increase >2 |
|
1.32 (0.73, 2.40)
|
1.35 (0.71, 2.58)
|
BMI Decrease <2 |
|
1.12 (0.64, 1.96)
|
1.01 (0.55, 1.87)
|
BMI Decrease >2 |
|
2.27 (1.32, 3.91)
|
2.10 (1.17, 3.81)
|
Did Not Complete High School |
|
|
1.27 (0.82, 1.97)
|
Never Married |
|
|
0.49 (0.23, 1.08)
|
Divorced |
|
|
1.08 (0.64, 1.84)
|
Smoking |
|
|
1.50 (0.92, 2.44)
|
Cognitive Impairment |
|
|
2.45 (1.59, 3.79) |
Other Findings
- More than half of the participants at baseline were in the normal BMI category of 18.5 to 24.9 and only 3.5% were considered underweight
- Almost 60% lost weight between 1991 and 1996
- BMI at CSHA1 was not a significant predictor of all-cause mortality between CSHA2 and CSHA3
- A significant decrease in BMI, regardless of BMI category, predicted death (odds ratio, 2.10; 95% confidence interval, 1.17, 3.80)
- Other factors predictive of death were age and cognitive impairment without dementia.
A two-unit change in BMI is a significant predictor of mortality in community-dwelling seniors without dementia. This BMI change translates into approximately five kg to seven kg over a five-year period or about one kg per year. Such a weight change is potentially important and future work should examine yearly weight change to determine if rate of weight change has an influence on mortality.
Government: | Seniors' Independence Research Program, National Health Research and Development Program of Health Canada | ||
Not-for-profit |
|
Authors note that there were very few seniors in the underweight category (3.5%), as well as the fact that those included in the analysis were "survivors," as the subjects who developed dementia were excluded.
Quality Criteria Checklist: Primary Research
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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) | N/A | |
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) | N/A | |
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? | Yes | |
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? | Yes | |
2.3. | Were health, demographics, and other characteristics of subjects described? | Yes | |
2.4. | Were the subjects/patients a representative sample of the relevant population? | Yes | |
3. | Were study groups comparable? | N/A | |
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? | N/A | |
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? | N/A | |
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? | Yes | |
4.1. | Were follow-up methods described and the same for all groups? | Yes | |
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%.) | N/A | |
4.3. | Were all enrolled subjects/patients (in the original sample) accounted for? | Yes | |
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? | Yes | |
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.) | Yes | |
5.3. | In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? | Yes | |
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? | Yes | |
6.3. | Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? | Yes | |
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? | Yes | |
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? | N/A | |
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 | |