- Click here for explanation of classification scheme.

To assess the association between the amount, types, and intensity of exercise in relation to risk of CHD in a large cohort of men.

Was not explicitly stated, but we can assume these:

*male gender

*Health professional (dentist, optometrist, pharmacist, podiatrist, osteopath, and veterinarian)

*40-75 years of age

*Free of:  cardiovascular dz (MI andgina, &/or coronary revascularization & stroke) & cancer other than nonmelanoma skin cancer prior to 1986

*Able to climb stairs and walk

*Men with a diagnosis of cardiovascular dz (MI, angina, &/or revascularization & stroke) & cancer other than nonmelanoma skin cancer prior to 1986

*Men w/ a CHD event during the follow-up were excluded from analyses in the subsequent intervals.

*Men who reported difficulty climbing stairs or walking were excluded from analysis at each time point starting from 1988

*Men were excluded throughout the study if they drastically reduced their levels of activity (>20 MET-h/wk) from one questionnaire to the next.

Recruitment:  Men enrolled in the Health Professionals' Follow-up Study.  This article did not explain how these men were recruited, nor did they give a reference for this process.  All that was stated was that they were health professionals. 

 

Design:  Prospective cohort of 44,452 men enrolled in the Health Professionals' Follow-up Study.  They were followed up at 2 year intervals from 1986-January 31, 1998.

*Follow-up questionnaires were sent in 1988, 1990, 1992, 1994, 1996, & 1998 to update information on potential risk factors & to identify newly Dx'ed cases of CHD & other illnesses.

*Leisure time physical activity was assessed every 2 years between 1986 and 1996, using the question: "During the past year what was your average time per week spent at each activity [walking (also walking pace), hiking, jogging, running, bicycling, lap swimming, tennis, squash or racquetball, calisthenics, or rowing]?"  Heavy outdoor work was added in 1988 and wt training in  1990. 

*Validity & reproducibility of the physical activity questionnaire was assessed in 1991 when 238 participants in the study completed a 1-week activity log at 4 periods corresponding to different seasons throughout the year.

 

Blinding used (if applicable):  N/A

 

Intervention (if applicable):  N/A

 

Statistical Analysis:  Main analyses- 1) used the cumulative avg of physical activity levels from all available questionnaires up to the start of each 2-year follow-up interval.  Additional analyses were performed using baseline levels of activity and simple updated levels of physical activity in which CHD was predicted only from the most recent questionnaire  2) Tests for trend were calculated by assigning the median values to increasing categories of activity  3) RR's were initially calculated adjusting for age  4) Cox proportional hazard models were used to estimate RRs of CHD over each 2-year follow-up interval using the cumulative avg of the reported levels of activity on prior questionnaires, adjusting for other potential confounders  5) Analyzed cumulative, simple-updated, and baseline (1986) activity as categorical and continuous variables  6) Corrected RRs corresponding to increments of simple-updated and baseline physical activity using the method of Rosner et al (Rosner B, Willett WC, Spiegelman D.  Correction of logistic regression relative risk estimates and confidence intervals for systematic within-person measurement error.  Stat Med.  1989;8:1051-1069; discussion 1071-1073)  7) Multivariate models included alcohol intake, family history of MI, use of vitamin E supplement, hx of DM, hypertension, & hypercholesterolemia at baseline, and quintiles of dietary intake of trans fatty acids, polyunsaturated fat, fiber, & folate.  Secondary analyses- 1) additionally controlled for BMI to estimate how this potential intermediate factor would affect RRs  2) Interaction between physical activity and obesity was assessed by the difference in -2 log likelihood  b/w the model containing the interaction w/ obesity in 2 categories (BMI<30, BMI>30) and the main effects model  3) Performed a propensity analysis in which they used logistic regression modeling to predict the highest as opposed to the lowest quintile of physical activity.  Demographic, clinical, & dietary variables were included in this.  The resulting propensity scores were used to match men from the two groups

 

Timing of Measurements: Follow-up questionnaires were sent every 2 years after the initial start of the study (1986=baseline, 1988, 1990, 1992, 1994, 1996, & 1998

 

Dependent Variables

• Occurrence of fatal CHD & nonfatal MI between the return of the 1986 questionnaire and January 31, 1998.  Self reported MI's were confirmed by a review of medical records based on criteria that included characteristic symptoms with either typical ECG changes or elevations of cardiac enzymes.  Probable cases of MI (no available records but confirmed by hospitalization & info from telephone interview/letter) were also included in the analysis after ensuring that results were not appreciably different from those including definite cases alone.  Deaths were reported by next of kin, work associates, and postal authorities.  In case of persistent nonresponse, the National Death Index was used to identify deceased cohort members.  Fatal CHD was confirmed by reviewing medical recoreds or autopsy reports.  Sudden deaths(ie, deaths w/in 1 hr of symptom onset in men w/out known dz that could explain death)  were included in the fatal CHD category. 

 

Independent Variables:  age, gender, activity level, BMI, dietary intake, alcohol intake, smoking status, hx of DM/HTN/hypercholesterolemia, use of supplements, family Hx of MI, ethnicity, economic status, mental status

 

Control Variables:  N/A

 

Initial N: 51,529 men, US health professionals

Attrition (final N):  44,452 men

Age: 40-75 years of age

Ethnicity: not available

Other relevant demographics: men who lived in the United States

Anthropometrics: Was not provided, however, the men were classified into three categories based on BMI (<25, 25-29.9, >30)

Location:  United States 

 

*Physically more active men tended to have lower BMIs, lower intakes of total fat and saturated fat, higher intakes of fiber and alcohol, a higher prevalence of vitamin E supplement use, and a lower prevalence of smoking & hypertension.

*During a 475,755 person-years follow-up, there were 1700 new documented cases of CHD. 

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                Cumulatively Updated Vol of Physical Activity by Quintile

Model                        1               2                3                   4                5

Age-adjusted            1.00           0.85           0.78              0.72           0.58

                                            (0.74-0.98)  (0.67-0.92)   (0.62-0.83) (0.49-0.68)

Multiv. Model 1*       1.00           0.90           0.84              0.80            0.65

                                            (0.78-1.03)  (0.73-0.98)   (0.68-0.92)  (0.56-0.77)

Multiv. Model 2**     1.00           0.90           0.87              0.83            0.70

                                            (0.78-1.04)  (0.75-1.00)   (0.71-0.96)  (0.59-0.82)

Multiv. Model 3^       1.00           0.93           0.90              0.87            0.74

                                            (0.80-1.06)  (0.78-1.05)  (0.71-1.01)   (0.63-0.87)

Multiv. Model 4^^     1.00           0.90           0.88              0.84            0.72

                                            (0.78-1.04)  (0.76-1.01)   (0.72-0.98)  (0.61-0.85)

*Adjusted for alcohol consumption, smoking, family hx of MI, & nutrient intake

**Adjusted for covariates in model 1 & for the presence of DM, high cholesterol levels, and HTN at baseline

^Adjusted for the covariates in model 2 and for BMI

^^Adjusted for the covariates in model 2, w/ physical activity volume in MET-hours per week and intensity in METS included in the same model

Side note:  All of the above had a P<0.001 for trend 

___________________________________________________________

1) Age-adjusted RRs across quintiles of total physical activity decreased monotonically and were modestly attenuated after adjustment for alcohol consumption, smoking, family history of MI before age 50, and nutrient intake.  The association was further attenuated by additionally adjusting for baseline presence of HTN, DM, and high cholesterol levels.  The RR comparing extreme quintiles was 0.70 (P<0.001 for trend).  Using simple updated and baseline physical activity, the corresponding RRs were 0.70 (P<0.001) and 0.77 (P<0.001).  Adjustment for BMI did not appreciably alter these results. 

2) Secondary analysis of propensity-matched men, showed that those who were at the highest quintile of activity still had a reduced CHD risk compared with those in the lowest quintile

3) When physical activity was modeled as a continuous variable, every 50 MET-h/wk increase of cumulatively updated physical activity was associated w/ a 26% reduction in risk of CHD.  The association was strengthened considerably after correction for measurement error.

4)  When analyzed separately, exercise intensity was related to reduced risk of CHD.  Multivariate analysis was used to assess if exercise intensity is related to CHD risk independent of exercise volume and the RRs corresponding to moderate and high exercise intensity were 0.94 and 0.83, respectively, compared w/ that for low exercise intensity (P=.02 for trend).  When assessed as a continuous variable, exercise intensity was related to a reduction in risk of 4% for each 1-MET increase independent of the total exercise volume.

5) Based on supplementary analyses, compared w/ men who maintained a low intensity of exercise, men who maintained a high level of intensity had an RR of 0.72, and those who increased intensity from low to high over time had an RR of 0.88

6) The RRs across quintiles of physical activity, adjusted for alcohol consumption, smoking, family hx of MI before age 50 years of age, nutrient intake, and baseline presence of HTN, high cholesterol, and DM were 1.0, 0.91, 0.87, 0.81, and 0.66 (P<0.001) 

7) When they evaluated the effect of physical activity across different subgroups defined by established risk factors for CHD (smoking, alcohol, obesity, HTN, family hx of MI, age, and presence of high cholesterol) an inverse association was observed in all groups.  However, the interaction b/w obesity status and physical activity was not statistically sig (P=0.09) 

Other Findings

*Running, jogging, rowing, and racquet sports were associated w/ reduced risk in age-adjusted analyses.  In multivariate analyses including previously mentioned covariates plus all activities, running and rowing remained significant predictors of CHD.  Running for one or more hours per week was associated w/ a 42% risk reduction and rowing for one or more hours per week was associated w/ an 18%risk reduction compared with men who didn't engage in these activities.  Cycling and swimming weren't associated w/ risk.

*Compared with men who didn't perform resistance training, the RRs for men who performed resistance training for less than 30 mins or for 30 or more mins per week were 0.83 and 0.65, respectively (P<0.001).  In multivariate analyses that also controlled for other types of physical activity, wt training for 30 minutes or more per week was associated w/ a significant 23% risk reduction (P=0.03 for trend)

*Total walking volume was associated w/ reduced risk of CHD in age-adjusted analysis.  In multivariate analysis, risk of CHD was reduced only for men in the highest quintile, corresponding to 14.75 MET-h/wk or more, w/ an 18% reduction in risk of CHD (P=0.04 for trend)

*Walking pace was significantly associated w/ reduced risk in age-adjusted and multivariate models.

*When analyzed in the same multivariate model w/ walking MET-hours and compared w/ walking at an easy pace, the RRs corresponding to normal pace, brisk pace, and very brisk pace were 0.72, 0.61, and 0.51, respectively (P<0.001 for trend).  Thus, walking pace is relatd to reduced CHD risk over and above the effect of walking volume.  

 

*Increased total physical activity was associated w/ reduced risk of CHD in a dose-dependent manner.  This inverse association was not explained by other known coronary risk factors, including BMI.  Exercise intensity was associated w/ an additional risk reduction.  Running, wt training, and rowing were each associated with reduced risk.  Walking pace was strongly related to reduced risk independent of walking MET-hours.  Thus, increasing intensity of aerobic exercise from low to moderate and from moderate to high, and adding wt training to the exercise program are among the most effective strategies to reduce the risk of CHD in men.

Government:

NIH

*The authors stated the strengths of the study (prospective design, large size of cohort, detailed info on exposure and covariates, extensive follow-up time, strict and uniform criteria for coronary events and relative homogeneity of socioeconomic status among subjects).

*They also indicated the limitations of the study (self-report of physical activity, cannot completely rule out the possibility of residual & unmeasured confoundings and cannot draw a causal relationship simply based on these data due to the observational nature of this study; when specific activities were analyzed, such as swimming and cycling, the findings were limited by their low range of exposure and some participants who performed these activities may have done them at lower intensities or spent less than reported time in actual exercise).

*One has to be cautious as to why these men chose to be in the study.  This could be a confounding factor.

*Inclusion criteria was not explicity stated.