COPD: Determination of Energy Needs (2007)

Citation:

Prescott E, Almdal T, Mikkelsen KL, Tofteng CL, Vestbo J, Lange P.  Prognostic value of weight change in chronic obstructive pulmonary disease:  results from the Copenhagen City Heart Study.  Eur Respir J 2002;20:539-544.

PubMed ID: 12358326
 
Study Design:
Cohort Study
Class:
B - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To prospectively study whether changes in BMI in subjects with COPD independently predict mortality. 
Inclusion Criteria:
  • Individuals aged > 20 years
  • Living in Copenhagen
Exclusion Criteria:
  • Self-reported asthma
  • Missing data on crucial variables
Description of Study Protocol:

Recruitment

Subjects from Copenhagen City Heart Study.  Population derived from random, age-stratified sample of 19,329 individuals.

Design

Cohort Study.

Blinding used (if applicable)

Not applicable.

Intervention (if applicable)

BMI was determined on 2 occasions with an interval of 5 years and subjects were thereafter followed for mortality for up to 18 - 20 years.

Statistical Analysis

To assess independent contribution of changes in BMI to mortality in COPD, Cox proportional hazards model was used.  Only interaction terms reaching statistical significance were included in the final model.  Results of regression analyses are given in terms of estimated rate ratio with corresponding 95% confidence intervals.

Data Collection Summary:

Timing of Measurements

Measurements completed and subjects folllowed for up to 18 - 20 years.

Dependent Variables

  • Mortality measured through Notification of Death and cause of death obtained from national Board of Health 

Independent Variables

  • BMI

Control Variables

  • Age
  • Smoking habits
  • Baseline BMI
  • Lung function measured using spirometer
Description of Actual Data Sample:

Initial N: 10,424 subjects available, but after application of exclusion criteria, 1,612 subjects with COPD were used in the analysis, 736 females, 876 males. 

Attrition (final N):  1,612 subjects

Age:  mean age females:  55.8 +/- 9.0 years, males:  56.6 +/- 9.7 years

Ethnicity:  not mentioned

Other relevant demographics:

Anthropometrics:

Location:  Denmark 

 

Summary of Results:

 

   COPD: FEV1/FVC <0.07

Weight loss >3 BMI units

2.14 (1.18 - 3.89)
Weight loss 1 - 3 BMI units 1.31 (0.89 - 1.92) 
Weight gain 1 - 3 BMI units 0.83 (0.53 - 1.32)
Weight gain >3 BMI units 0.95 (0.43 - 2.08)
Test for linear trend p = 0.01
Initial BMI < 20 1.68 (1.06 - 2.66)
Initial BMI 20 - 24.9 ref
Initial BMI 25 - 29.9 0.66 (0.44 - 0.98)
Initial BMI > 30 0.72 (0.38 - 1.35) 
Test for linear trend p = 0.002

 FEV1 % predicted (per 10% decrease)

1.50 (1.37 - 1.65)

Other Findings

The proportion of subjects who lost > 1 unit BMI (~3.8 kg) between the 2 examinations was significantly associated with level of COPD, reaching 30% in subjects with severe COPD.

After adjusting for age, smoking habits, baseline BMI and lung function, weight loss was associated with higher mortality in both persons with and without COPD - rate ratio for weight loss >3 BMI units 1.71 (95% confidence interval 1.32 - 2.23) and 1.63 (95% confidence interval 1.38 - 1.92), respectively.

Weight gain was associated with increased mortality, but not significantly so in subjects with COPD.

Risk of COPD-related death increased with weight loss - rate ratio 2.14 (95% confidence interval 1.18 - 3.89) but not with weight gain - rate ratio 0.95 (95% confidence interval 0.43 - 2.08).

In subjects without COPD or with mild-to-moderate COPD, the effect of weight change was the same irrespective of initial weight.

In subjects with severe COPD, there was a significant risk ratio modification (p = 0.045) between effect of baseline BMI and weight change:  in the normal-to-underweight (BMI < 25), best survival was seen in those who gained weight, whereas for the overweight and obese (BMI > 25), best survival was seen in stable weight. 

Author Conclusion:
In conclusion, the present study has shown that weight loss is common in chronic obstructive pulmonary disease and is an independent risk factor for all-cause mortality.  In addition, weight gain seems to have a protective effect in under- and normal-weight subjects with severe chronic obstructive pulmonary disease.  These results should be tested in an intervention study.
Funding Source:
Reviewer Comments:
Study based on same data as Vestbo et al.  Measurements not well described.  Body composition measurements not included in this study.
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? 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? 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? 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? 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? N/A
  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%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? N/A
  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.) N/A
  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? Yes
  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? 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? Yes
  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? ???
  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? ???
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  7.6. Were other factors accounted for (measured) that could affect outcomes? ???
  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