EAL

FNOA: Assessment of Overweight/Obesity (2012)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To determine age-specific risk of all-cause mortality across levels of BMI during specified intervals of a 26-year follow-up period.

Inclusion Criteria:

Resident of California at time of cohort entry in 1960
Seventh-day Adventist
Female
Completed a four-page American Cancer Society questionnaire at baseline
Never a smoker
Non-Hispanic white
Aged 30-74 at time of cohort entry.

Exclusion Criteria:

Not enrolled in the Adventist Mortality Study
Male
Former or current smoker
Age less than 30 years or greater than 74 years at time of cohort entry
Non-white.

Description of Study Protocol:

Recruitment

In 1960, 27,530 California Seventh-day Adventists aged 30 and older were invited to complete a four-page American Cancer Society questionnaire through church membership.

Design

Prospective cohort study

Blinding used

None

Intervention

Not applicable

Statistical Analysis

Baseline characteristics of the study population were compared across quintiles of BMI by chi-square analysis or one-way analysis of variance
The relationship between BMI and all-cause mortality was investigated by computing the hazard ratio for each BMI quintile from a Cox proportional hazard model with "time on study" as the time variable.

Data Collection Summary:

Timing of Measurements

Eligible subjects completed a four-page questionnaire upon cohort entry in 1960 including information on demographics, medical history, and lifestyle characteristics. Deaths were ascertained during 26 years of follow-up by computer-assisted record linkage with the California Death Certificate File and telephone contact.

Dependent Variables

All-cause mortality

Independent Variables

Age
BMI.

Control Variables

Prevalence of pertinent diseases
Alcohol use
Vegetarian vs. non-vegetarian diet
Marital status
Education attainment.

Description of Actual Data Sample:

Initial N: 12,576 women
Attrition (final N): All included in final analysis
Age: 30-74 years old at time of cohort entry
Ethnicity: Non-Hispanic white women
Other relevant demographics: Seventh-day Adventists
Anthropometrics: None relevant outside of the studied variables
Location: California, USA.

Summary of Results:

Key Findings

Among middle-aged women (ages 30-52 years at cohort entry), a weak linear relationship existed between BMI and all-cause mortality during years one to eight of follow-up (median age attainment, 51 years); a significant linear relationship was observed during years nine to 14 of follow-up (median age attainment, 57 years) and a significant, non-linear (U-shaped relationship) was observed during years 15-26 of follow-up (median age attainment, 68 years).
Among older women (ages 55-74 years at cohort entry), a significant non-linear relationship (U-shaped) was observed between BMI and all-cause mortality during the first one to eight years of follow-up (median age attainment, 71 years); a significant linear relationship was observed during years nine to 14 of follow-up (median age attainment, 77 years) and during years 15-26 of follow-up (median age attainment, 87 years).

BMI and all-cause mortality risk among middle-aged women

Follow-up time	BMI <21.3 Deaths/PY (HR; 95% CI)	BMI 21.3-22.9 Deaths/PY (HR; 95% CI)	BMI 23.0-24.8 Deaths/PY (HR; 95% CI)	BMI 24.9-27.4 Deaths/PY (HR; 95% CI)	BMI >27.4 Deaths/PY (HR; 95% CI)	P for linear trend	P for non-linear trend
One to eight years	24/11,566 (1.0; --)	22/12,682 (0.79; 0.44-1.40)	16/11,509 (0.56; 0.30-1.06)	21/9,411 (0.87; 0.48-1.58)	25/8,430 (1.14; 0.64-2.03)	--	0.03
Nine to 14 years	16/8,532 (1.0; --)	16/9,383 (0.84; 0.42-1.68)	17/8,525 (0.86; 0.43-1.72)	21/6,925 (1.23; 0.63-2.38)	28/6,161 (1.81; 0.96-3.41)	0.02	0.21
15-26 years	64/16,509 (1.0; --)	53/18,248 (0.69; 0.48-0.99)	70/16,522 (0.87; 0.62-1.23)	68/13,223 (0.98; 0.68-1.39)	102/11,474 (1.64; 1.19-2.26)	--	0.003

PY: Person-years

BMI and all-cause mortality risk among older women

Follow-up time	BMI <21.3 Deaths/PY (HR; 95% CI)	BMI 21.3-22.9 Deaths/PY (HR; 95% CI)	BMI 23.0-24.8 Deaths/PY (HR; 95% CI)	BMI 24.9-27.4 Deaths/PY (HR; 95% CI)	BMI >27.4 Deaths/PY (HR; 95% CI)	P for linear trend	P for non-linear trend
One to eight years	85/5,499 (1.0; --)	65/5,637 (0.81; 0.59-1.12)	56/7,909 (0.50; 0.36-0.70)	85/9,062 (0.66; 0.49-0.89)	147/9,478 (1.07; 0.82-1.40)	--	<0.00001
Nine to 14 years	86/3,539 (1.0; --)	79/3,799 (0.93; 0.69-1.27)	102/5,458 (0.84; 0.63-1.12)	138/6,151 (1.02; 0.78-1.33)	183/6,087 (1.34; 1.04-1.74)	0.002	0.12
15-26 years	182/5,386 (1.0; --)	200/5,734 (1.11; 0.91-1.36)	287/8,223 (1.13; 0.93-1.36)	323/9,321 (1.12; 0.93-1.33)	353/8,605 (1.29; 1.08-1.54)	0.001	0.57

PY: Person-years

Author Conclusion:

An elevation in risk of disease-related mortality among women with a BMI of greater than 27.4kg/m² is consistently shown over time and is in agreement with numerous studies linking obesity to an elevated risk of death.
Among middle-aged women (30-54 years), a linear relationship between BMI and mortality was evident during short-term follow-up through their middle-aged years. During long-term follow-up, through a median age of 68 years, a U-shaped relationship was evident.
Among older women (55-74 years), a U-shaped relationship was evident during short-term follow-up through a median age of 71 years. This trend was reduced to a linear relationship during long-term follow-up through a median age of 87 years.
The findings from long-term follow-up of middle-aged women and short-term follow-up of older women are suggestive of an etiology occurring during the fifth to seventh decade of life that increases the risk of disease-related mortality among a proportion of lean women who were probably lean during middle age.

Funding Source:

Government:

National Institutes of Health

Reviewer Comments:

Large sample size and 26 years of follow-up. Authors note that the anthropometric data were based on self-report, but that in similar studies of Adventists, the correlation between self-reported and in-person measurement of weights were high (R=0.94); thus, measurement error is not likely to have substantially influenced results.

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)	N/A
	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)	N/A

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)	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?	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?		Yes
	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?	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?		No
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	No
	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.)	No
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	No
	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?	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?	???
	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