DLM and Physical Activity

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To compare the roles of walking and vigorous exercise in the prevention of coronary and cardiovascular events in a large, ethnically diverse cohort of postmenopausal women. 
Inclusion Criteria:

 Was never explicitly stated, but this can be assumed:

*postmenopausal

*50-79 years of age at entry of study

*free of: any medical condition (Coronary heart dz, stroke, cancer, class IV CHF, Obstructive lung dz requiring O2, severe chronic liver or kidney dz), alcoholism, mental illness, dementia, or nonambulatory

*Completely filled out questionnaire (including physical activity section)

Exclusion Criteria:

*presence of any medical condition associated w/ predicted survival of less than 3 years (e.g., class IV CHF, Obstructive lung disease requiring supplemental O2, severe chronic liver or kidney dz), alcoholism, mental illness, or dementia

*At base line if they had a history of coronary heart dz, stroke, or cancer; were nonambulatory (unable to walk at least one block), or had missing data on the physical-activity questionnaire

Description of Study Protocol:

Recruitment: Provided a reference to find this information [Langer RD, White E, Lewis CE, et al.  Baseline characteristics of the participants in the Observational Study of the Women's Health Initiantive and reliability of baseline measures.  Ann Epidemiol (in press).] 

 

Design: Prospective, ethnically and racially diverse, multicenter clinical trial and observational study

*All women in the study were required to go to the clinic for base-line screening.  The completed self-administered questionnaires related to personal and family medical history, physical activity, smoking, diet, and other behavioral lifestyle-related factors.  Clinical measurements included ht, wt, waist and hip circumferences, and blood pressure.

*Recreational physical acitivity was assessed by a detailed questionnaire on the frequency and duration of walking and of several other types of activity (strenuous, moderate, and mild - giving examples for each intensity)

*Participants were asked to estimate the number of hours per day spent engaged in sedentary behavior, including time spent sitting as well as lying down or sleeping

*A sample of participants (1092 women) were recruited into a reliability study to assess the reproducibility of selected questionnaires, including the physical activity assessment

Blinding used (if applicable): N/A

 

Intervention (if applicable): N/A

 

Statistical Analysis:  PRIMARY ANALYSES (Used the detailed physical-activity assessment at baseline)-Age adjusted relative risks were computed (as the incidence rate in a specific category of activity divided by the incidence rate in the lowest quintile, with adjustment for one-year age categories), tests of linear trend (statistical significance were two-sided), Cox proportional-hazards regression (to adjust for potential confounding variables), differences in the results for activity according to race, age, and BMI were assessed SECONDARY ANALYSES- excluded data for the first year follow-up in order to minimize potential bias caused by the presence of subclinical disease

 

Data Collection Summary:

Timing of Measurements: date of return of the baseline questionnaire to the date of a confirmed cardiovascular event, death from any cause, or August 27, 2000, whichever came first.

 

Dependent Variables

  • Newly diagnosed coronary heart disease (nonfatal MI or death from coronary causes) and total cardiovascular events (MI, death from coronary causes, coronary revascularization, angina, CHF, stroke, or carotid revascularization)  Newly diagnosed cardiovascular events were identified on the basis of annual mailed follow-up questionnaires (response rates > 95%).  These were measured by study physicians with no knowledge of the self-reported risk factor status reviewed by the records.  Study physicians confirmed events by medical records (elevated cardiac enzymes, diagnostic tests, diagnosis by a physician and medical treatment, cause of death on death certificate) 

 

Independent Variables:  age, postmenopausal status, gender, activity level, ht, wt, waist to hip circumference, ethnicity, BMI, smoking status, alcohol consumption, use of hormone replacement therapy, parental history of premature MI, education, familiy income, dietary variables, hypertension history, diabetes, high cholesterol levels, functional status, mental/emotional health

 

Control Variables: N/A

 

Description of Actual Data Sample:

Initial N: 93,676 women

Attrition (final N):  73,743 women (61,574 were non-Hispanic White, 5661 were non-Hispanic Black, 2880 were Hispanic, 2288 were Asian or Pacific Islander, 1340 were American Indian or of other racial or ethnic background) 

Age: 50-79 years of age

Ethnicity: Noted above in attrition (non-Hispanic White, non-Hispanic Black, Hispanic, Asian or Pacific Islander, American Indian or other racial/ethnic background)

Other relevant demographics: postmenopausal

Anthropometrics: *Baseline anthropometrics were given in a different article referenced in this paper [Langer RD, White E, Lewis CE, et al.  Baseline characteristics of the participants in the Observational Study of the Women's Health Initiative and reliability of baseline measures.  Ann Epidemiol (in press).] *BMI ranges that were given included:  BMI<25.0 (n=30,583), BMI:25.0-29.9 (n=24,590), BMI> 30.0 (n=16,806)

Location: 40 different clinical centers across the United States (they are all listed in the appendix of the article)

 

Summary of Results:

                                                    Quintile of total MET-Hr per Week

Category                                    1             2               3                4                5

                                                (lowest)

Total Exercise

Coronary Heart Dz

    Age-adjusted RR (95%CI)    1.00        0.73           0.69            0.68             0.47

                                                           (0.53-0.99) (0.51-0.95)  (0.50-0.93) (0.33-0.67)

Total CVD                

    Age-adjusted RR (95% CI)    1.00        0.83           0.72            0.63            0.55

                                                            (0.71-0.95) (0.62-0.84)  (0.54-0.74)  (0.47-0.65)

    Multivariate RR (95% CI)        1.00       0.89           0.81            0.78            0.72

                                                            (0.75-1.04)  (0.68-0.97)  (0.66-0.93)  (0.59-0.87)

Walking

Total CVD

    Age-adjusted RR (95% CI)       1.00        0.88           0.70             0.66            0.58

                                                               (0.77-1.01)  (0.60-0.81)  (0.57-0.77)  (0.56-0.82)

    Multivariate RR (95% CI)          1.00        0.91           0.82             0.75            0.68

                                                                (0.78-1.07)  (0.69-0.97)  (0.63-0.89)  (0.56-0.82)

Vigorous Exercise

Total CVD

     Age-adjusted RR (95% CI)      1.00         0.87            0.73             0.69            0.60

                                                                (0.72-1.04)  (0.58-0.92)  (0.53-0.89)  (0.47-0.76)

*P Value < 0.001 for all of the above

*The total physical-activity score (in MET hours per week) at base line had a strong inverse relation with the risk of coronary heart dz during the follow-up period.

*In age-adjusted analyses, the RR declined w/ increasing quintiles of the total MET score.

*Risk reductions for increasing categories of walking (P for trend= 0.004) were similar to those for increasing categories of vigorous exercise (P for trend= 0.008)

*Reductions in the risk of total cardiovascular events w/ increasing categories of total MET scores, walking, and vigorous exercise were similar to those for the risk of coronary disease.

*In multivariate analyses, after simultaneous control for covariates, physical activity remained a predictor of the subsequent risk of cardiovascular events.  For increasing quintiles of the total MET score P was < 0.001.  Increasing categories of walking were associated with similar reductions in risk (P for trend <0.001), which were also similar to the risk reductions w/ vigorous exercise.

Other Findings

*In 5.9 years of follow-up (mean, 3.2 years; total 232,971 person-years), documented 345 newly Dx'ed cases of coronary dz (287 nonfatal MI & 58 deaths from coronary causes), 309 strokes, 1551 first cardiovascular events among the 73,743 women.

*Women who either walked or exercised vigorously at least 2.5 hours per week had a risk reduction of approx 30%.  Simialr reductions in the risk of cardiovascular events w/ an increasing MET score were observed for white and black women (for other racial/ethnic groups, the samples were not large enough to be analyzed separately), as well as for women in different categories of age or BMI.

*Increasing categories of walking were inversely associated w/ the risk of cardiovascular events.

*Women who engaged in both walking and vigorous exercise had greater reductions in cardiovascular risk than those who did either one alone.

*Walking pace was also an important determinant of reduction in cardiovascualr risk.  As compared w/ women who never or rarely walked, women who walked at faster paces of 2-3 mph, 3-4 mph, & >4 mph had relative risks of cardiovascular dz of 1.00, 0.86, 0.76, 0.58, respectively (P for trend=0.002).

*In relation between hours spent sitting, as well as lying down or sleeping, the RR of cardiovascular dz was 1.38 among women who spent 12-15 hrs per day lying down or sleeping and 1.68 among women who spent at least 16 hours per day sitting, as compared w/ those who spent less than 4 hours per day.  Other durations of sitting or lying down were not significantly associated w/ cardiovascular risk.

 

Author Conclusion:

The prospective data from an ethnically diverse cohort of postmenopausal women indicate that both walking and vigorous exercise are associated with substantial reductions in the incidence of cardiovascular events.  A graded inverse relation was observed among both white and black women, lean and obese women, and younger and older women.  In contrast, prolonged time spent sitting predicts increased risk.

The results also lend further support to current federal exercise guidelines that endorse moderate-intensity exercise for at least 30 mins on most, and preferably all days of the week.

Funding Source:
Reviewer Comments:

*They state the strengths of the study (Including, it is a prospective design, large size, racially and ethnically diverse cohort, had a detailed assessment of physical activity as well as sedentary behavior, & had uniform and strict criteria for the coronary and cardiovascular end points, had a high f/u rate and detailed info about potential confounding variables.  The exclusions and prospective design minimized any influence of preexisting dz on the level of physical activity.  Secondary analyses excluding data from the first year of follow-up in order to minimize bias related to the presence of subclinical dz.)

*They also indicated study limitations (Physical activity was assessed by questionnaire, possible residual confounding by lifestyle-related factors, and it is not an entirely representative cross-section of women in the US despite the fact that it had more diverse racial and ethnic background & socioeconomic status individuals than in most previously studied cohorts.

*Inclusion criteria was not explicitly given in this article.  It referenced it from another article.

*There was no mention about subjects who may have been on cholesterol lowering meds or HBP meds and if that may affect risk of coronary dz events.

*Something to consider is bias from the subjects in that it was a volunteer option.  Does that mean this group is healthier?

*Something that could be looked into would be how exercise would benefit those already with cardiovascular events.  Will it prevent or decrease any future incidents?

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) 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")? N/A
4. Was method of handling withdrawals described? N/A
  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? 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.) 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? 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? 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? 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? 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