DM: Physical Activity (2007)

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

To study in men with diabetes

1) the risk of mortality associated with fitness and BMI when examined as continuous and categorical variables

2) the dose-response relationship between fitness and mortality both with adjustment for BMI and within levels of BMI.

Inclusion Criteria:

All were participants in the Aerobics Center Longitudinal Study (ACLS)

  • male
  • examined at least once during 1970 to 1995
  • completed at least one year of follow-up
  • diagnosis of diabetes or fasting plasma glucose level greater than or equal to 7.0 mmol/l
Exclusion Criteria:
not specified
Description of Study Protocol:

Recruitment: Recruitement for the ACLS study is not specified in this article

Design Participants were given a thorough clinical examination, including a maximal exercise test, and then followed until their deaths or until December 31, 1996. 

Blinding used (if applicable):  not applicable 

Intervention (if applicable):  not applicable

Statistical Analysis

  • mean and SD of each variable calculated with participants categorized as surviviors or decedents
  • log-linear proportional hazards models used to assess the independent association of fitness and BMI as continuous variables as well as to evaluate the contributions of traditional CVD risk factors
  • subjects divided into MET quartiles and risk of mortality assessed by four log-linear proportional hazards models, adjusted for
    • age and year of examination
    • same as above + non-modifiable risk factors
    • all of the above + modifiable risk factors
    • all of the above + BMI
  • the association of fitness to mortality within levels of BMI by cross-tabulated MET and BMI categories to create 11 fitness-BMI categories (not enough subjects for the MET quartile 4 obese cell)
  • Log-linear proportional hazard models were used to estimate adjusted relative risks for mortality for each fitness-BMI category
  • the continuous variables of METS and BMI used to test linear trends
  • analyses repeated using body fat percentage quartiles instead of BMI categories


Data Collection Summary:

Timing of Measurements:  Followed for 1 - 26 years

Dependent Variables

  • mortality as reported in the National Death Index

Independent Variables

  • blood pressure
  • anthropometry, including body composition by hydrostatic weighing for more than 1400 of the participants
  • maximal exercise test on a treadmill; patients began walking on a treadmill at 3.3 mph with no elevation. After the first minute elevation was increased to 2% and was increased 1% every minute until the 25th minute, when increases in elevation stopped and speed was increased by 0.2 mph each minute
  • self-reported smoking history
  • history of CVD:  history of heart attack, stroke, abnormal resting or exercise EKG, parental history of premature CVD (before age 50)
  • regular physical activity, defined as reporting regular walking, jogging, cycling, or participation in a racket sport

Control Variables


Description of Actual Data Sample:

Initial N: 2196 men with diabetes, followed for 1-26 years

Attrition (final N): 2196 men, until death

Age: 49.3±9.5 years

Ethnicity: predominantly non-Hispanic white

Other relevant demographics: well-educated and currently or previously employed in professional or executive positions

Anthropometrics reported in results

Location: United States


Summary of Results:

Baseline characteristics of 2196 men with diabetes grouped by survival status, Aerobics Longitudinal Study, 1970-1996







Person-years of observation  29008











Exercise tolerance (METS)  10.5±2.1  8.8±1.9  


total cholesterol level, mg/dl  225.9±43.4  235.0±47.7  


fasting glucose, mg/dl  134.3±49.3  146.0±60.7  


systolic blood pressure, mmHg  126.0±15.0  132.8±17.3  


diastolic blood pressure, mmHg  83.5±9.7  85.7±11.4  


never smoked, %  36.1  26.5  0.007
Past smokers, %  44.0  49.1  
current smokers, %  19.9  24.4  
physically active, %  46.8  38.9  0.01
hypertension, %  30.2  44.4  <0.0001
family history of premature CVD, %  15.0  17.1  0.38
prevalent CVD, %  15.3  34.5±  <0.0001

Age and examination year adjusted for risk of death according to cardiorespiratory fitness (maximal METS attained during the exercise test), BMI, and other clinical, health status, and lifestyle variables.

  BMI only   Treadmill METS only   BMI and Treadmill METS  
Variable RR and 95% CI P RR and 95% CI P RR and 95% CI P
Fitness,(for each 1-MET increase)      0.750.70-0.81  <0.0001  0.74(0.68-0.80)   <0.0001
BMI for each 1-kg/m2 increment  1.04(1.02-1.07) 0.003       0.98(0.95-1.01)  0.27
fasting glucose, for each 10 mg/dl increment  1.04(1.02-1.05)  <0.0001   1.041.02-1.05   <0.0001  1.04(1.02-1.05)   <0.0001
systolic blood pressure (for each 10 mm/Hg increase)  1.12(1.04-1.20)  0.002 1.10(1.02-1.17 ) 0.02  1.10(1.02-1.18) 0.01 
Prevalent CVD  1.80(1.38-2.34)   <0.0001  1.34(1.02-1.76) 0.04  1.30(0.98-1.72)   0.07
Family history of premature CVD  1.45(1.05-1.99) 0.023  1.39(1.01-1.91)  0.04  1.37(1.00 1.89) 0.05 
total cholesterol (for each 1--mg/dl increment  1.03(1.00-1.06) 0.04  1.02-(1.00-1.05)  0.10  1.02(1.00-1.05)   0.12
Past cigarette smoking  1.23(0.92-1.64) 0.16  1.08-(0.81-1.44)  0.61 1.07(0.80-1.43)   
current cigarette smoking  1.75(1.24-2.46) 0.001  1.27(0.89-1.80)  0.19  1.25(0.88-1.77)  0.21

Relative Risk (RR) and 95% confidence Interval forrisk of mortality across fitness caegories (quartiles of maximal METS attained during the exercise test) and BMI categories.  

  Fitness Quartiles (METS)           BMI categories      
Adjustments <_8.82 8.83-10.08 10.09-11.71 >11.71 (ref) P for trend Adjustments <25.0 (ref) 25.0-29.9 >-30.0 P for trend
Age, examination year 5.72(3.54-9.24) 3.01(1.84-4.93) 1.64(0.97-2.79) 1.0 <0.0001 Age, examination year 1.0 1.23(0.93-1.63) 1.86(1.34-2.59) 0.0003
Above + nonmodifiable risk factors 5.23(3.22-8.49) 2.93(1.79-4.80) 1.62(0.95-2.75) 1.0 <0.0001 Above + nonmodifiable risk factors 1.0 1.23(0.93-1.63) 1.82(1.31-2.53) 0.0005
Above + modifiable risk factors 4.29(2.61-7.05) 2.68(1.62-4.44) 1.58(0.92-2.70) 1.0 <0.0001 Above + modifiable risk factors 1.0 1.07(0.81-1.43) 1.51(1.08-2.10) 0.02
Above + BMI 4.49(2.64-7.64) 2.77(1.65-4.66) 1.60(0.93-2.76) 1.0 <0.0001 Above + fitness (treadmill METS) 1.0 0.81(0.61-1.09) 0.81(0.56-1.16) 0.22

Author Conclusion:

Fitness has a strong and independent inverse association with mortality in men with diabetes and this result was seen in all BMI and body fatness groups.

The findings show a steep inverse relation between fitness and mortality and that this relation is evident within all BMI strata.

Approximately half of all obese individuals in this study were in the lowest fitness quartile and these low-fitness obese men had a 5.6-fold higher risk of death than men in the reference group- the most fit quartile of normal-weight men.

Obese men with fitness levels greater than the lowest quartile were at no increased risk for mortality when compared with men in the reference group, but this group had a relatively small sample size.

79% of men in the highest quartile of fitness reported participating in regular physical activity, a rate that was 3 times higher than in men in the lowest fintess quartile.  Therefore we assume that the objective measure of fitness used in our study in an excellent marker of physical activity habits.

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? N/A
  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? N/A
  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? 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? 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? 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? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  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? 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? 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? 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)? 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