EAL

DM: Prevention of Type 2 Diabetes (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

The purpose was to determine whether effectiveness of lifestyle interventions is influenced by severity of insulin resistance and/or insulin secretion.

Inclusion Criteria:

Impaired glucose tolerance (IGT) determined by 2-hour, 75 g glucose tolerance test using WHO criteria for IGT.

Exclusion Criteria:

Did not meet WHO criteria for IGT
Presence of diagnosed type 2 diabetes

Description of Study Protocol:

Recruitment: This paper provides analysis of 284 subjects for whom insulin resistance and insulin secretion measures were available; The original sample of 577 people were recruited from half of the clinics in the Hei Long Jiang province in northern China. The clinics served 126,715 people over 25 years of age.

Design: RCT; subjects were randomized by clinic into four subgroups (see intervention below) to examine effects of lifestyle intervention on development of type 2 DM

Blinding used: unclear

Intervention:

controls
diet alone
exercise
diet and exercise

This paper looks at the influence of insulin resistance and insulin secretion on results of the lifestyle interventions.

Statistical Analysis

To measure the effect of insulin resistance and insulin sensitivity in development of DM, the investigators used a derived model. (HOMA) to compute an index. Log-transformed values were used to normalize distribution of variables. They then used ANOVA to determine differences among groups. Proportional hazards analysis used to assess predictors of NIDDM (insulin resistance, insulin sensitivity, glucose, ß-cell function, and interactions).

Data Collection Summary:

Timing of Measurements

Data collected at baseline exam after 10-12 hour fast:

blood pressure, height, weight, fasting blood glucose, lipids, urine glucose and albumin and questionnaire to assess medical and family history for diabetes;
plasma insulin concentrations measured in these 284 of the original 577 subjects

Data collected at baseline and every 2 years:

Oral glucose tolerance test (OGTT)
Food intake and physical activity as deterined by questionnaire/interviews

Dependent Variable

development of type 2 DM (plasma glucose or oral glucose tolerance test)

Independent Variables

insulin resistance
insulin secretion
lifestyle intervention (diet, exercise, or diet and exercise as compared to control group)

Control Variables

Description of Actual Data Sample:

Initial N: Original study had 577; In this analysis, a subset of 284 individuals for which insulin resistance and insulin secretion was measured at baseline: (147 males, 137 females)

Attrition (final N): n/a

Age: mean age 45

Ethnicity: Chinese

Other relevant demographics: mean BMI 25.8 ±3.8 years

Anthropometrics

Location: Da Qing, China

Summary of Results:

Variables

Control

P-Value (RR)

Diet

P-Value (RR)

Exercise

P-Value (RR)

Diet & Exercise

P-Value (RR)

Adjusted for IR & IS

(1.0)

0.0507 (0.64)

0.0354 (0.62)

0.0006( 0.42)

Adjusted for IR, IS, BMI

(1.0)

0.0842 (0.67)

0.0550 (0.64)

0.0006 (0.42)

IR is insulin resistance; IS is insulin sensitivity; BMI is body mass index.

Other Findings

Effect of lifestyle intervention greatest in less insulin resistant groups 1 and 2 for which there was approximately 50% decrease in NIDDM incidence. In groups 3 and 4 who expressed greater insulin resistance, there was still 30% decrease in NIDDM incidence when compared with controls with corresponding IR values.

Author Conclusion:

Lifestyle change alone is less effective when subjects have higher degrees of insulin resistance. Evaluating insulin sensitivity may be useful when defining optimal strategies for prevention of NIDDM.

Funding Source:

Reviewer Comments:

It is unfortunate that the article has some typographical errors. For example, age of IGT controls is listed a 97±1.04 years (other groups range from 42.5 to 44.3 mean years). For correct information the reviewer referred back to the original Da Qing IGT and Diabetes Study article: Pan X-R, et al. Effects of diet and exercise in preventing NIDDM in people with impaired glucose tolerance. Diabetes Care. 1997;20(4):537-544.

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?	Yes
	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?	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%.)	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?	N/A
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?	???
	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.)	???
	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?	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?	Yes
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	Yes
	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?		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)?	???
	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