DLM and Physical Activity
To review the effects of aerobic exercise training (AET) on blood lipids and assess dose-response relationships and diet interactions.
- Does the available evidence support the hypothesis that endurance exercise training has a favorable influence on the blood lipid profile relative to future risk of CHD?
- Does blood lipid responses to training differ by study subjects' sex, age, or race, baseline lipid levels, and baseline relative body wt & its change w/ training?
- Are lipid responses to exercise related to intensity, duration, weekly volume of energy expenditure, length of endurance program, & associated changes w/ training in VO2 max?
Studies published on or after 1987
Studies in English language
Greater than 12 week endurance program
*consisted of supervised structured group aerobic exercise programs in sedentary, apparently healthy, white individuals, unless indicated.
*Few studies w/ monitored "lifestyle activities" &/or home exercises.
*A few with resistance training
Studies before 1987
Less than 12 week endurance exercise program
Studies not of English language
Recruitment - English literature search using Medline & Index Medicus using key words (physical activity, blood lipids, lipoproteins, alone or in combination) for studies published later than or in 1987; Additional studies used that were published before 1987 came from references by predious reviewers.
Design - Meta-analysis
Blinding used (if applicable)- N/A
Intervention (if applicable)- N/A
Statistical Analysis- Pearson correlation, stepwise multiple linear regression two-tailed t-test
Timing of Measurements- Before exercise program and after exercise program
Dependent Variables- % change from before to after training in lipid parameters
Independent Variables- baseline age, sex, TC, LDL-C, HDL-C, TG, BMI, VO2 max, previous medical Hx (ex: one study contained men w/ HTN); KJ/week of exercise performed, changes after training in body wt, VO2 max, blood lipids
Control Variables
Training program:
- type of activity: (walking, jogging, swimming, cycle ergometer, stairclimber, rowing machine, strength training, dancing, circuit training, ball games, ski machine, step aerobics)
- length of the program
- intensity (almost all studies it was moderate to hard), frequency (in almost all it was 3-5 times/week >30 mins),
- duration of sessions (12 weeks to 2 years)
Initial N: 51 studies (28 randomized control)
Attrition (final N): supposedly 51, however, only 44 are in Table 3 (it summarizes each study); 4700 participants
Age: men aged 17-80 and women aged 17-80 per tables (text states 18-80 with a mean age of 46.6 + or - 0.35);
Ethnicity: majority white, text states 2 studies included African-Americans, however table indicates 3 studies included African Americans (Duncan et al, 1991; Leon et al, 2000; Kokkinos et al, 1998), text states 0 hispanics as subjects however tables indicate 1 study included Hispanics (Duncan et al, 1991), 2 studies with Japanese individuals (Sunami et al, 1999; Motoyama et al, 1995)
Other relevant demographics: premenopausal women, postmenopausal women {Cauley et al, 1987 (203 subjects); Lindheim et al, 1994 (95 subjetcs); Klenbanoff et al, 1998 (18 subjects); Fox et al, 1996 (40 subjects)}, 1 study included subjects with antihypertensive meds (Kokkinos et al, 1998)
Anthropometrics: BMI categories- < 25 (10 studies), 25-29.9 (25 studies), >30 (9 studies); Mean baseline lipid levels- TC 204.5 + 33.9 mg/dL, LDL 136.5 + 22.5 mg/dL, HDL 45.6 + 9.3 mg/dL, TG 125 + 27.8 mg/dL
Location: Researchers from University of Minnesota
Table 5:Correlations of baseline and posttraining variables with changes in blood lipids (N=61 study groups involving about 2200 participants)
Percent changes w/ Taining
Variable Total Cholesterol LDL HDL TG
Pretraining
age (yr) -0.219 -0.183 -0.038 -0.154
weight (kg) -0.110 -0.124 0.182 -0.439**
BMI (kg/m2) -0.006 -0.013 0.130 -0.313*
VO2 max -0.216 -0.249 0.103 -0.439**
TC -0.269 -0.094 0.024 -0.077
LDL -0.420** -0.232 -0.067 -0.065
HDL -0.148 0.027 -0.462** 0.348*
TG -0.297 -0.139 0.164 -0.290*
Wks of training -0.137 -0.330* -0.073 0.081
Exercise volume 0.205 -0.045 0.078 -0.097
Posttraining
Weight loss (kg) 0.415** 0.381** -0.227 0.443**
change VO2 max (%) 0.027 0.196 0.222 -0.084
change TC 1.00 0.800** -0.154 0.550**
change LDL 0.800** 1.00 -0.402** 0.128
change HDL -0.154 -0.233* 1.00 -0.069
change TG 0.550** 0.128 -0.175 1.0
*P<0.05, **P<0.01
(analysis was limited to groups which performed exercise without concomitant dietary changes)
1)Significant inverse assoc found b/w the change in HDL with training and baseline HDL (r= -0.462). This association was even stronger in studies reporting significant increases in HDL with training (r= -0.676)
2)Significant association with increased HDL with a change in LDL w/ training (r= -0.402)
3)All lipid parameters generally improved in studies in which there was a substantial weight loss (>a4 kg), usually associated with a concomitant hypocaloric diet
Per question #1 in purpose: The bulk of the evidence supports the hypothesis that endurance exercise training in both RCT and non-RCT, despite great inconsistencies. Exercise training also appears to attenuate the reduction in HDL accompanying a decreased dietary intake of sat fat and cholesterol to promote reduction of LDL.
Per question #2 in purpose: Adult men & women appear to respond similarly to training. Age doesn't appear to be a predictor of lipid responsiveness to training. There is limited data on racial and ethnic differences. Baseline body wt was found to be inversely related to change in TG; Studies in which a sizable wt loss was obtained while holding the percent of energy intake constant generally had a favorable effect on the entire lipid/lipoprotein profile; however a concomitant reduction in percent energy from fat clearly reduces the HDL response to exercise. Baseline lipid levels appear to strongly influence the lipid response to training.
Per question #3 in purpose: Insufficient data to conclusively establish a dose-response relationship b/w intensity and volume of exercise and lipid responses. Most of the reviewed studies showing HDL changes used an exercise prescription w/ moderate- to hard-intensity activities for at least 30 minutes, three times per week (can raise HDL). No significant correlation was found b/w the increas in VO2 max and change in HDL with training
Government: | NHLBI, |
University/Hospital: | University of Minnesota Heart Disease Prevention Clinic, Universidad de Oriente (Venezuela) |
This review indicated the specific flaws of the various studies. The reviewer also listed 8 recommended study topics to improve current studies.
The problem with generalizing these articles is that they pertain to mostly healthy, white individuals.
Inclusion criteria indicated it used articles published >1987, however, additional studies published <1987 were used if they were identified by previous reviewers.
This analysis never explicitly stated what the exclusion criteria were. It was abstracted from the reading.
I think they should have discussed more in depth their findings when diet and exercise were combined. Indicate what was significant or not.
This analysis seemed to focus on HDL changes. I feel that all lipid parameters should have been discussed in more depth. They didn't discuss the significant changes (or p-value) revealed with the other lipid parameters
Quality Criteria Checklist: Review Articles
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Relevance Questions | |||
1. | Will the answer if true, have a direct bearing on the health of patients? | Yes | |
2. | Is the outcome or topic something that patients/clients/population groups would care about? | Yes | |
3. | Is the problem addressed in the review one that is relevant to dietetics practice? | Yes | |
4. | Will the information, if true, require a change in practice? | Yes | |
Validity Questions | |||
1. | Was the question for the review clearly focused and appropriate? | Yes | |
2. | Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? | Yes | |
3. | Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? | Yes | |
4. | Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? | Yes | |
5. | Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? | Yes | |
6. | Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? | Yes | |
7. | Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? | Yes | |
8. | Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? | Yes | |
9. | Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? | Yes | |
10. | Was bias due to the review's funding or sponsorship unlikely? | Yes | |