EAL

DLM: BMI (2001)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To assess the mortality over 12 years among white men and women who participated in the American Cancer Society's Cancer Prevention Study I (from 1960 through 1972) and to analyze mortality as a function of body mass index (BMI) across age groups.

Inclusion Criteria:

Adults 30 to 54 years of age
Non-medicated diastolic blood pressure (DBP) of 83 to 89mmHg and systolic blood pressure (SBP) less than 140mmHg
BMI: Men: 26.1 to 37.4kg per m²; women: 24.4 to 37.4kg per m².

Exclusion Criteria:

Current treatment with medications that would alter blood pressure
Clinical or laboratory evidence of CVD
Diabetes mellitus
Renal insufficiency: Serum creatinine greater than 1.7mg per dL for men and greater than 1.5mg per dL for women
Current or planned pregnancy.

Description of Study Protocol:

The authors studied mortality over 12 years among white men and women who participated in the American Cancer Society’s Cancer Prevention Study I (from 1960 through 1972)
The 62,116 men and 262,019 women included in this analysis had never smoked cigarettes, had no history of heart disease, stroke or cancer (other than skin cancer) at baseline in 1959 to 1960, and had no history of recent unintentional weight loss
The date and cause of death for subjects who died were determined from death certificates
The associations between BMI and mortality were examined for six age groups
Multicenter trial to evaluate lifestyle interventions
- Subjects were randomly assigned with equal probability to one of four groups:
  - Weight loss only
  - Sodium reduction only
  - Combined weight loss and sodium reduction
  - Usual care (controls)
The proportional-hazards analysis (PROC PHREG, SAS Institute, Cary, NC) is used to assess associations between BMI and mortality from all causes and from cardiovascular disease. Body mass index was examined as both a continuous and a categorical variable. Likelihood-ratio tests were used to test for interactions in the proportional-hazards models. The linear trends for the relative risks associated with an increase of one in the BMI across age groups were tested by weighted linear regression analysis. The inverse of the variance of the risk estimates was used for the weight.

Data Collection Summary:

Study protocol:
- Baseline blood pressure measurements taken at three screening visits, each separated by seven to 45 days. Three readings of SBP and DBP were averaged.
- Blood pressure and weight were measured every six months after randomization to the end of follow-up at 36, 42 or 48 month
- Dietary intake was assessed by 24-hour recall and physical activity by questionnaire
- Intervention included individual counseling session, followed by 14 weekly group meetings led by RD’s or health educators. This was followed by six, bi-weekly group meetings and then monthly group meetings.
- Intervention: Three-year program of self-directed behavior change, nutrition education, social support and to increase physical activity to 30 to 45 minutes per day, four to five times per week at moderate intensity.
Outcome measures: Blood pressure.

Description of Actual Data Sample:

N: 595 assigned to weight loss and 596 assigned to usual care
Demographics: 66% men, 79% white, 18% black, 51% college graduates
Mean age: 43 years at baseline.

Summary of Results:

81% of the subjects attended at least half of the sessions they were expected to attend during the first six months; 64% attended at least 80% of their assigned sessions. Follow-up at the end of the study (36 months) was 92% for the intervention group and 93% for the usual care for weight measurements and 89% and 86% for blood pressure measurements. Mean weight change from baseline in the intervention group was –4.4kg at six months, -2kg at 18 months and –0.2kg at 36 months. Mean weight change in the control group was 0.1, 0.7 and 1.8kg for the same time period. (P<0.001). Blood pressure was significantly lower in the intervention than the control group at six, 18, and 36 months.
The risk ratio for hypertension in the intervention group was 0.58 (95% CI, 0.36 to 0.94) at six months; 0.78 (CI, 0.62 to 1.00) at 18 months and 0.81 (CI, 0.70 to 0.95) at 86 months. In subgroup analysis, subjects in the intervention group who lost at least 4.5kg at six months and maintained this weight reduction for the next 30 months had the greatest reduction in blood pressure and a relative risk for hypertension of 0.35 (CI, 0.20 to 0.59). Clinically significant long-term reductions in blood pressure and reduced risk for hypertension can be achieved with even modest weight loss.
Weight loss at six months was strongly related to attendance at the intervention sessions, but the relationship between attendance and weight diminished later in the trial. Subjects who successfully maintained weight loss of 4.5kg or more experienced a reduction in DBP that was sustained throughout the remainder of follow-up.
In contrast, SBP decreased over the initial six months but subsequently increased halfway to baseline levels even though weight loss was sustained which suggests that weight loss alone, even if maintained, may not be sufficient to prevent an age-related increase in SBP.

Author Conclusion:

Those who had the largest short-term weight loss (-6.6 kg) in six months attended 14 counseling sessions. In this study, BMI was estimated only once, at one age, for each subject. Thus, no conclusions can be drawn about the effect of changes in weight over time.The design of this study also did not allow the effects of age to be distinguished from temporal or birth-cohort effects. In addition, the fact that these data were collected between 1959 and 1972 may limit the generalizability of our results. Another limitation is the number of years of follow-up. Twelve-year mortality in a cohort of 30-year-old subjects is very different from that among 85-year-old subjects. Despite these limitations, the very large number of subjects in a wide range of age groups, the 12 years of follow-up information and the availability of information on both intended and unintended.
Weight loss made the Cancer Prevention Study I data set a rich resource for these analyses
Excess body weight increases the risk of death from any cause and from cardiovascular disease in adults between 30 and 74 years of age. The relative risk associated with greater body weight is higher among younger subjects.

Funding Source:

Government:

National Institute of Diabetes and Digestive and Kidney Diseases and by the Institute of Nutrition

Reviewer Comments:

Greater BMI was associated with higher mortality from all causes and from cardiovascular disease in men and women up to 75 years of age. However, the relative risk associated with greater BMI declined with age. This may be due to aging changes and increased risk of other factors.
Authors agreed there are limitations for this study.

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?	N/A
	1.2.	Was (were) the outcome(s) [dependent variable(s)] clearly indicated?	N/A
	1.3.	Were the target population and setting specified?	Yes
2.	Was the selection of study subjects/patients free from bias?		N/A
	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?	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?	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?	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%.)	N/A
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	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?		N/A
	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?	N/A
	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?	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?	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?	Yes
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