EAL

DM: Prevention of Type 2 Diabetes (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

Researchers used data from the University of Pennsylvania Alumni Health Study to determine whether higher levels of physical activity are associated with a lower incidence of NIDDM.

Inclusion Criteria:

Men who enrolled at the University of Pennsylvania between 1928 and 1947 and who responded to a questionnaire about lifestyle habits and health in 1962 and 1976.

Exclusion Criteria:

Diagnosis of diabetes on 1962 questionnaire.

Description of Study Protocol:

Recruitment: Questionnaires on lifestyle habits and health were sent to alumni men who attended the University of Pennsylvania between 1928 and 1947.

Design: Cohort Study. Information on lifestyle and personal characteristics that were considered possible risk factors for the development of NIDDM was obtained from the 1962 questionnaire. They used the physical activity variable as an indicator of an individuals weekly energy expenditure, largely during leisure time. They assigned a specific number of kilocalories of energy expenditure to each activity reported on the 1962 questionnaire in order to compute a physical-activity index.

Blinding used (if applicable): not applicable

Intervention (if applicable): not applicable

Statistical analysis: They determined the relation between the predictor variables in 1962 and the incidence of diabetes during the 14-year follow-up period. For the descriptive analyses, they classified the men according to their 1962 levels of physical activity and suspected risk factor for diabetes and compute age-adjusted rates of diabetes per 10,000 man years of observation for each level of the risk variables studied. Relative risks and significance values for linear trend were computed with the Mantel extension of the Mantel-Haenszel test. To test for the independence of the association between physical activity and the development of NIDDM, they used the proportional-hazards regression model.

Data Collection Summary:

Timing of measurements:

Baseline data collected in 1962: weight, height, family history of diabetes, hypertension, and leisure time physical activity index
Similar questionnaire completed in 1976 that caputured diagnosed of diabetes over the 14-year period between 1962 and 1976
Physical exam data available from 1928-1947 for 4965 alumni including height and weight.

Dependent variables:

Diagnoses of type 2 diabetes mellitus

Independent variables:

Physical activity index calculated in kcal/wk for vigorous, moderate, and flights of stairs or blocks walked.

Control variables:

Age
BMI at baseline (1962)
History of hypertension
Parental history of diabetes
Change in weight from the time of college physical examinations to 1962

Description of Actual Data Sample:

Initial N: 5990 men completed the 1962 and 1976 quesionnaires

Attrition (final N): 5990

Age: In 1962, the men in the study population ranged in age from 39 to 68 years old

Ethnicity: not given in article

Other relevant demographics: none

Anthropometrics: BMI ranged from 14.1 to 46.0

Location: Alumni from the University of Pennsylvania

Summary of Results:

Other Findings

Of the 5990 men who met the study criteria, 202 had developed type 2 diabetes mellitus by the end of 1976. The sensitivity of the questionnaires in identifying patients with diabetes was 85% and the specificity was 97% as estimated on the basis of mail or telephone surveys of 2200 alumni who were physicians.

Leisure-time physical activity was inversely related to the development of type 2 diabetes mellitus.

The incidence rates of type 2 diabetes mellitus decreased as energy expenditure increased from <500 kcal to 3500 kcal.

For each 500 kcal increase in energy expenditure, the age-adjusted risk of type 2 diabetes mellitus was decreased by 6% (relative risk, 0.94, 95% CI, 0.90 to 0.98). This association remained when the same when the data were adjusted for obesity, hypertension, and family history for diabetes.

The protective effect of physical activity was strongest in those at increased risk for type 2 diabetes mellitus-- increased BMI, history of hypertension or family history of diabetes. These factors + weight gain since college were independent predictors of the disease.

Author Conclusion:

The data reported here support the concept that diabetes may be prevented by increased overall activity and that vigorous activities, including swimming, tennis and running may have an even stronger protective effect than less vigorous activity.

The data also suggest that increased energy expenditure should be encouraged in subgroups of the population that are at increased risk for type 2 diabetes including those with hypertension, family history of diabetes and obesity.

We believe that exercise should be recommended as an adjunct to proper diet and weight control for the prevention of type 2 diabetes mellitus.

Funding Source:

Government:

NHLBI

Not-for-profit

Foundation associated with industry:

Reviewer Comments:

The findings of this study are consistent with others that demonstrate a decreased risk for type 2 diabetes mellitus with regular physical activity even when other risk factors for diabetes are present. However, it is important to remember that NIDDM diagnoses was based on self-report and not on clinical diagnoses.

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?	???
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?	Yes
	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")?	No
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?	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?	???
	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?	Yes
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	Yes
	6.6.	Were extra or unplanned treatments described?	Yes
	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?		No
	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?	No
	7.5.	Was the measurement of effect at an appropriate level of precision?	No
	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