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SCI: Lipid Abnormalities (2007)

Citation:

Bauman WA, Adkins RH, Spungen AM, Herbert R, Schechter C, Smith D, Kemp BJ, Gambino R, Maloney P, Waters RL. Is immobilization associated with an abnormal lipoprotein profile? Observations from a diverse cohort. Spinal Cord. 1999;37(7):485-493.

PubMed ID: 10438115
 
Study Design:
Cohort Study
Class:
B - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

The purpose of this study was to compare components of the serum lipid profile, using the same commercial laboratory between two relatively large cohorts: those with spinal cord injury (SCI) and a comparable age-, gender-, and ethnic-matched able-bodied control population.

Inclusion Criteria:

Out-patients with SCI being seen for routine annual physical examination at the Comarr Spinal Injury Clinic at Rancho Los Amigos Medical Center, Downey, California from May 1994 to May 1996 and controls from the Bridge and Tunnel Officers of the New York Metropolitan Transportation Authority employed from 1993 to 1995, and those who had retired since 1985.

Exclusion Criteria:

Subjects with missing data or serum triglycerides greater than three standard deviations from the mean were excluded (10 in the group with SCI and 31 in the control group).

Description of Study Protocol:

Recruitment

  • Subjects with SCI were recruited at their routine annual physical examination at the Comarr Spinal Injury Clinic at Rancho Los Amigos Medical Center, Downey, California from May 1994 to May 1996
  • Controls from the Bridge and Tunnel Officers of the New York Metropolitan Transportation Authority employed from 1993 to 1995, and those who had retired since 1985.

Design

  •  The two cohorts were compared and divided into two categorical groups for gender and ethnicity [white (non-Latino), African American and Latino]. 
  • SCI group were evaluated at their routine physical examination.
  • Subjects in the control group completed a physical activity qquestionnarie obtained from The Lipids Research Clinics Program Prevalence Study.
  • All laboratory analyses for both cohorts were performed by the same clinical laboratory facility. Serum lipid profiles were performed on SCI subjects after an overnight fast and after a 4 h fast for the controls.

Blinding used (if applicable)

 Not described

Intervention (if applicable)

 N/A

Statistical Analysis

  • Results were reported as mean ± standard error of the mean (SEM).
  • Unpaired t-test was used for comparisons between the SCI and control groups for age and BMI, and on the dependent variables of total cholesterol, triglycerides, HDL-cholesterol, LDL-cholesterol and total cholesterol.
  • Comparison between males and females for the above variables were also performed with the unpaired t-test.
  • Analysis of variance (ANOVA) was used for the comparisons among the subgroups factored by ethnicity.
  • Statistical power calculations were determined for serum HDL-cholesterol for the groups and each of the subgroup comparisons.
  • A stepwise regression model using 12 continuous variables of interest to determine the most important predictors of HDL-cholesterol was used.
  • A multiple regression model was used to determine group differences for serum HDL-cholesterol controlling for TG levels.
  • Chi-squared analyses were performed to determine distribution differences between the SCI and control groups for gender and ethnicity.
  • Simple regression analyses were used to determine the associations between HDL-cholesterol and TG: BMI and estimated percent fat. 
  • Two analysis of covariance (ANCOVA) models were used to determine the covariance of the two groups on either BMI or estimated percent body fat with HDL-cholesterol.
Data Collection Summary:

Timing of Measurements

Data was obtained at baseline for both groups from 1993 to 1996..

Dependent Variables

  • Total cholesterol
  • Triglycerides
  • HDL-cholesterol
  • LDL-cholesterol
  • Total cholesterol/HDL-cholesterol ratio

Independent Variables

  • Study group (control and SCI group)
  • Gender (male, female)
  • Ethnic group (white, African-American, Latino)

 

Control Variables

 A random iterative process was used to produce similar histogram distributions of gender and ethnicity in order to control for age, gender and ethnic distribution between the two groups.

Description of Actual Data Sample:

 

Initial N: Subjects: n=656. Controls n=526. 

Attrition (final N): Subjects: n=320. Controls: n= 303.

Age:

  • SCI group: 41 years ± 0.62 (range 20-77).
  • Control group: 42 years ± 0.57 (range 21-75)

Ethnicity:

SCI group:

  • White 47% (n=149)
  • African American 28% (n=88)
  • Latino 26% (n=83)

Control

  • White 56% (n=169)
  • African American 29% (n=87)
  • Latino 16% (n=47)

Other relevant demographics:

SCI group:

  • BMI>27.8: 28% (n=88)
  • Male: 73% (n=233)
  • Female: 27% (n=87)

Control:

  • BMI>27.8: 64% (n=189)
  • Male: 81% (n=244)
  • Female: 20% (n=59)

 

Anthropometrics:

BMI and % body fat were significantly different at baseline for controls and SCI group (P<0.0001)

At baseline controls had significantly more BMIs > 27.8 than SCI gorup (P<0.0001).

Location:

  • Subjects: Downey, California. 
  • Controls: New York Metropolitan area

 

 

Summary of Results:

 Comparison of serum lipid results between the study groups.

 

 

SCI Group

n=320

Mean ± SEM

Control group

n=303

Mean ± SEM

Statistical Significance of Group Difference

P

TC

190±2.27 207±2.34 <0.0001*

TG

108±3.08

118±3.25

<0.05*

HDL-c

 42±0.79

 47±0.67

<0.0005*

LDL-c 126±2.13 137±2.16 <0.0001* 
TC HDL-c  5.0±0.11  4.6±0.08 <0.01*

 

Other Findings

  • The serum HDL-c was signficantly lower in males with SCI than males in the control group (P<0.0001), but not the females. 
  • Within subgroups for whites and Latinos, HDL-c values were also lower in subjects with SCI than in controls, P<0.0001 and P<0.05 respectively) but not for African Americans.
  • African Americans with SCI had had higher HDL-c values than whites or Latinos wtih SCI (P<0.0001). 
  • In persons with SCI, HDL-c values were inversely related to body mass index and estimated percent body fat (P<0.0001).
Author Conclusion:

In white and Latino males, but not in females or African Amercians, immobilization from SCI appears to be associated with lower HDL-c values than in controls.

Funding Source:
Government: national institute for disability and rehabilitation research
Reviewer Comments:

Confounding factors were not inlcuded in the analysis.

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? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? No
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  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.) Yes
  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? No
  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")? Yes
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%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? Yes
5. Was blinding used to prevent introduction of bias? ???
  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? ???
  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? Yes
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? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
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? 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? ???
  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? ???
  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)? ???
  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