DM: Prevention and Treatment of CVD (2007)

Citation:
 
Study Design:
Class:
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Quality Rating:
Research Purpose:

1)  To evaluate the influence of dietary habits and lifestyle on plasma total homocysteine (tHcy) in subjects with type 2 diabetes in a Mediterranean population

2) To examine the potential differences in tHcy levels between diabetic and control subjects and the relationships between plasma tHcy levels and sex, age, anthropometric parameters, duration and degree of hyperglycemia, plasma vitamin B12 and folate levels, and insulin resistance in these subjects.

Inclusion Criteria:
  • type 2 diabetes
  • 40-75 years old
  • no history of nephropathy or microalbuminemia
  • no history of hypothyroidism, liver disease, active infections, autoimmune diseases, stage III or IV heart falilure according to NYHA criteria, uncontrolled hypertension, pregnancy, known vitamin B12 or folate deficiency, cancer or leukemia, psoriasis or alcohol abuse.
Exclusion Criteria:
  • taking medications known to affect plasma tHcy levels (methotrexate, phenytoin, fibrates, oral contraceptives, hormonal replacement therapy, sulfonamides, l-dopa, theophylline, and vitamin supplementation)
Description of Study Protocol:

Recruitment:

  • 126 type 2 diabetic patients were consecutively recruited from the outpatient diabetes clinic of the authors' hospital
  • 76 healthy controls matched for age, sex, and smoking habits to the diabetic patients were also recruited and were hospital staff and their relatives and friends

Design

  • dietary and physical activity records were obtained for the previous month as data collected for another, larger study
  • biological assays obtained once

Blinding used (if applicable):  not applicable 

Intervention (if applicable):  not applicable

Statistical Analysis

  • all variables were tested for normal distribution
  • skewed variables were log-trnasformed to improve normality for statistical testing and then were back-transformed for presentation in the tables.
  •  a two-sample t-test or a Wilcoxon test was used to dompare differences between non-diabetic and diabetic subjects.
  • a chi-square test was used for categorical variables
  • univariate linear regression analysis was applied to exaine the relationship between plasma tHcy  levels and the variables of interest in the control and the diabetic group.
  • multivariate linear regression analyses were performed to look for independent associations bwteen plasma tHcy levels and the variables that were found to have a statistical associaation (P<0.05) or a trend for an association (P <0.20) with the plasma tHCY concentration in univariate analysis
Data Collection Summary:

Timing of Measurements:  all measurements obtained once

Dependent Variables

  • plasma homocysteine (tHcy)
  • blood pressure
  • BMI
  • waist-to-hip ratio
  • folate
  • vitamin
    B12
  • lipids
  • HbA1c
  • creatinine
  • uric acid
  • glomerular filtration rate

Independent Variables

  • dietary habits; assessed using food frequency questionnaire that focused on fruits, vegetables, red meats, fish, coffee, and alcohol consumption
  • smoking habits; subjects classified as non-smokers, ex-smokers, or current smokers
  • physical activity records were used to obtain an account of all physical activities performed by the subject in the month prior to enrollment.  The data were expressed as (METS)-min per day (the product of the minutes for each activity times the MET intensity level)

Control Variables

  • in multivariate linear regression:
    • for control group:  age, sex, GFR, weekly dietary intake, physical activity
    • in the diabetic group:  age, sex, systolic blood pressure, GFR, duration of diabetes, plasma uric acid levels, and the amount of weekly consumption of fruit and vegetables. 
Description of Actual Data Sample:

Initial N: 126 diabetic subjects and 76 controls

Attrition (final N): as above

Age:  58.4±9.1 for subjects with diabetes

Ethnicity: not specified

Other relevant demographics: 53.2% of diabetic subjects were male

Anthropometrics

  • BMI 29.4±4.8 for subjects with diabetes
  • WHR 0.92±0.08 for subjects with diabetes
  • no siginificant differences between diabetic group and healthy group for age, gender, BMI, or WHR
  • systolic and diastolic blood pressures were significantly higher in the group with diabetes
    • SBP 123.5±14.7 in controls, 135.4 ±18.9, P=0.01
    • DBP 77.6±7.5 for controls, 82.7±9.5, P=0.03

Location: Greece

 

Summary of Results:

 

Variables

Control Group

 

Diabetic group

 

P value

Fasting glucose, mmol/l

 5.06±0.92  9.53±3.22

 <0.0001

HbA1c

 5.40±.3

 7.6±1.8

 <0.0001

Total Cholesterol, mmol/l

 5.64±1.05

 5.52±1.03

 0.81

HDL, mmol/l 1.18±0.28  1.12±0.55  0.04
LDL, mmol/l 3.88±1.09  3.72±0.92  0.27
Triglyceride, mmol/l 1.35±0.80  1.61±0.92  0.008
Uric Acid, mmol/l 0.24±0.06  0.24±0.07  0.99
Creatinine, micromol/l 82.2±12.4  75.1±15.0  0.60
GFR, ml/min 107.9±33.5  102.6±30.4  0.30
Folate nmol/l 14.5±6.0  19.4±14.6  0.01
B12, pmol/l 320.6±135.9  311.9±145.3  0.39
albumin, g/l 52.3±2.1  53.5±2.9  0.59
homocysteine, micromol/l 12.67±3.79  11.49±3.68  0.40

 

Other Findings

  • univariate linear regression analysis in non-diabetic subjects showed that plasma tHcy levels were significantly associated with male sex (P=0.04), portions of red meat consumed per week (P=0.005) and GFR (P=0.01) 
  • the same analysis in diabetic subjects showed significant relations between plasma tHcy levels and age (P=0.02), male sex (P=0.02), systolic blood pressure (P=0.03) plasma uric acid (P=0.001), GFR (P= 0.02) and the amount of the weekly consumption of fruit and vegetables (P=0.02)
  • multivariate linear regression analysis in the non-daibetic group, showed that onlyu GFR was independently and significantly associated with tHcy (P=0.03)
  • the same analysis in the diabetic group shoed that age (P=0.001), GFR(P<0.0001) and weekly consumption of fruits and vegetables (P=0.04)were independently and significantly associated with tHcy.

 

Author Conclusion:
  • Plasma tHcy levels do not differ between subjects with type 2 diabetes and non-diabetic subjects
  • In patients with type 2 diabetes, age, renal function, and weekly consumption of fruits and vegetables are important determinants of plasma tHcy levels
Funding Source:
Reviewer Comments:
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) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? No
  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? 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? 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? N/A
  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