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DM: Prevention of Type 2 Diabetes (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To examine the association between regular vigorous exercise and the subsequent incidence of type 2 diabetes in a prospective cohort of US women.

Inclusion Criteria:
  • Completed exercise frequency questionnaire in 1980
  • Diagnosis of type 2 diabetes mellitus after 1980
Exclusion Criteria:
  • Medical diagnosis of one of the following: diabetes mellitus, CHD, stroke, or cancer.
Description of Study Protocol:

Recruitment:  questionnaire sent to 121,700 female Registered Nurses in 11 US states.

Study Design:

Cohort Study.  The Nurses’ Health Study cohort was established in 1976 when 121,700 female RNs, 30 – 55 years of age residing in 1 of the 11 states responded to mailed questionnaires regarding their medical history and health practices and self-reported height and weight and followed for up to 8 years.

Blinding:  Endocrinologist blinded to self-reported diagnosis of diabetes confirmed the diagnosis of 61 of the 62 women. 

Intervention

1. Follow-up questionnaires biennially from 1976 to 1988.

2. Physical activity assessment in 1980 : validated questionnaire that asked the frequency of physical activity that was vigorous enough to cause sweating.

3. A  random review of medical records of 62 women by an Endocrinologist blinded to self-reported diagnosis of diabetes confirmed the diagnosis of 61 of the 62 women. 

Statistical Analysis

  • Incidence rates of type 2 diabetes were computed according to physical activity at baseline in 1980, with the follow-up period extending to the date of diagnosis of diabetes, or June 1, 1988.
  • rates of type 2 diabetes obtained by dividing the number of cases by person-years in each category of physical activity
  • Relative risk was determined after adjustment for age and BMI, with BMI updated every two years

 

Data Collection Summary:

Timing of Measurements:  Validated questionnaire regarding self-reported diagnosis of diabetes mailed in 1984, 1986, and 1988

Dependent Variable

Diagnosis of diabetes: >=1 of the following:

  •  fasting plasma glucose >=140 mg/dL along with one or more classic symptoms
  • random plasma glucose >=200 gm/dL
  • >=2 elevated plasma glucose measurements on different occasions
  • treatment with oral hypoglycemic medications

Independent Variables

  • subjects divided into 2 categories according to frequency of vigorous exercise
    • less than once a week
    • once or more per week
  • second analysis done with 5 categories: 0, 1, 2, 3 or 4 or more times per week

Control Variables

Multivariate analysis of

  • effects of physical activity
  • age
  • BMI
  • family history of diabetes
  • smoking
  • alcohol consumption
  • history of hypertension
  • high serum cholesterol
  • parental history of heart attack before age 60.

 

Description of Actual Data Sample:

Initial N:  87, 253 women met the criteria for this study.

Attrition (Final N):  92% of potential total person-years of follow-up.

Age:  30-55 years, 46.1 +/- 7.2

Ethnicity:  98% of the subjects were white.

Other relevant demographics:Family history of diabetes, 18.4%.  During followup from 1980 to 1988, 1303 women were diagnosed with type 2 diabetes mellitus.

Anthropometrics:  BMI 24.3 ±4.4

Location:  United States

Summary of Results:

 

Weekly Vigorous Exercise, 1980-88 No. Cases of Type 2 diabetes Age-adjusted Relative Risk Age and BMI- adjusted Relative Risk
No 844 1.0 1.0
Yes 459 0.67(0.6-0.75)* 0.84 (0.75-0.95)**
Total 1303    

* P<0.0001  **P<0.005

Other Findings

Women who engaged in vigorous exercise at least once a week had an age-adjusted relative risk of type 2 diabetes mellitus of 0.67 compared with women who did not exercise weekly (P < 0.0001).

After adjustment for BMI, the decrease in risk was attenuated but remained statistically significant (RR = 0.84, P = 0.005).

Among women who exercised at least once a week, there was no clear dose-response gradient according to frequency of exercise (exercising more than once a week did not decrease the risk more than once a week).

Family history of diabetes did not modify the effect of exercise, and risk reduction with exercise was evident in women regardless whether their weight was were normal or of they were obese.

Author Conclusion:

Our results indicate that physical activity may be a promising approach to the primary prevention of type 2 diabetes mellitus.

Further research is needed to assess the magnitude of the benefits of exercise and to determine the most effective exercise programs to decrease  the incidence of type 2 diabetes mellitus.

Funding Source:
Government: NIH
Reviewer Comments:

Only ~ 1/3 of the subjects participated in vigorous physical activity. However, many nurses do considerable walking during work hours.

This study showed a reduced risk for developing type 2 diabetes mellitus in women participating in physical activity only 1 day/week.

Physical activity was assessed only once, in 1980.  Potential changes in physical activity after that were not monitored.

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? 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? 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? No
  4.4. Were reasons for withdrawals similar across groups? ???
  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? 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? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? No
  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? 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? N/A
  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? 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)? No
  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