EAL

FNOA: Assessment of Overweight/Obesity (2012)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To ascertain the pattern of adult height change as a function of age and gender. To examine the effect of height change with age on BMI.

Inclusion Criteria:

Member of the Baltimore Longitudinal Study on Aging (BLSA)
Age 17 to 94 years at cohort entry
Non-Hispanic white
Three or more measurements of height taken at separate occasions over the course of the study.

Exclusion Criteria:

Race other than Non-Hispanic white
Less than three height measurements taken over the course of the study.

Description of Study Protocol:

Recruitment

Subjects recruited between 1958 and 1993 in the Baltimore Longitudinal Study of Aging in Baltimore, Maryland.

Design

Prospective cohort study

Blinding Used

Implied with measurements.

Statistical Analysis

Change in height with age included only those subjects whose height was measured three or more separate times
A two-stage random effects model was used to analyze the data
The first stage consisted of computing each subjects's rate of height loss by regressing the subject's heights on the ages at which heights were measured
The second stage began by characterizing each subject by height loss and age at enrollment
The subjects were assigned to one of nine groups on the basis of entry age
Within each age group, the subject-specific slope and entry age were averaged to produce a decade-specific mean slope and a decade-specific entry age
The sex-specific age differences in height were quantified by regressing height on age using both linear and quadratic models.

Data Collection Summary:

Timing of Measurements

Height was measured over the course of the cohort trial from 1958 to 1993. Frequency of follow-up varied by the date of cohort entry and compliance with follow-up regimen. Only subjects with height measured on at least three separate occasions were included in this analysis.

Dependent Variables

Height was measured in stocking feet using a moving anthropometer
BMI.

Independent Variables

Age
Gender.

Description of Actual Data Sample:

Initial N:
- 1,068 men and 390 women in cohort
- 1,430 men and 654 women analyzed cross-sectionally
Attrition (final N): All accounted for
Age: 17 to 94 years at cohort entry
Ethnicity: Non-Hispanic white
Other relevant demographics: Cohort described as "generally well educated, middle to upper-middle class, community dwelling and in good health."
Location: Baltimore, MD, US.

Summary of Results:

Key Findings

In both men and women, the longitudinal slope of height on age became increasingly negative with increasing age. The rate of height lost increased with increasing age.
Age explained 33% of the variance in the rate at which men's height changed. Age explained 28% of the variance for women (P<0.001 for both men and women).
For men, the relationship between age and rate of change in height was curvilinear (P<0.001). For women, there was a suggestion that the quadratic equation fit the data better than the linear equation did (P<0.16).
The rate of loss of height was a function of initial height for men, but not for women. Taller men lost height faster than shorter men did.

Change in Height with Age Among Men in the Baltimore Longitudinal Study of Aging

Age Group (years)*	Mean Height (cm)	Mean Slope (SE) (cm per year)	P-value
17 to 19	180.8	0.106 (0.080)	0.25
20 to 29	179.2	0.013 (0.006)	0.04
30 to 39	178.9	-0.024 (0.006)	0.00
40 to 49	176.7	-0.063 (0.005)	0.00
50 to 59	175.1	-0.102 (0.009)	0.00
60 to 69	174.2	-0.143 (0.011)	0.00
70 to 79	172.8	-0.192 (0.013)	0.00
80 to 89	171.1	-0.308 (0.038)	0.00
90 to 94	167.6	-0.575

*Subjects assigned to age groups on the basis of their age at first visit.

Change in Height with Age among Women in the Baltimore Longitudinal Study of Aging

Age Group (Years)*	Mean Height (cm)	Mean Slope (SE) (cm per year)	P-value
20 to 29	166.7	-0.005 (0.022)	0.81
30 to 39	164.0	-0.026 (0.021)	0.21
40 to 49	165.1	-0.110 (0.024)	0.00
50 to 59	160.7	-0.165 (0.015)	0.00
60 to 69	160.6	-0.223 (0.016)	0.00
70 to 79	157.5	-0.290 (0.030)	0.00
80 to 89	154.3	-0.472 (0.113)	0.00
90 to 93	157.7	-0.336	0.00

*Subjects were assigned to age groups on the basis of their age at first visit.

Cross-sectional analysis:

Height decreased with age among both men and women
The relation between age and height was curvilinear; a quadratic equation described the relation better than a linear equation did (partial F-test, P<0.02). Height was lost at an increasing rate with increasing age.
For men, age explained 14% of the variance in height; for women, age explained 22% of the variance (P<0.001 for men and women).

Author Conclusion:

In the Baltimore Longitudinal Study on Aging population, men and women lose height with age (cross-sectional analysis) and with aging (cohort analysis). The relationship between height and aging is curvilinear for men and somewhat curvilinear for women indicating that the rate of height loss increases with increasing age.
Height loss begins around age 30 and accelerated with increasing age
Cumulative height loss from age 30 to age 70 averaged 3cm for men and 5cm for women; by age 80, it increased to 5cm for men and 8cm for women
BMI is generally assumed to be an age-invariant measure of obesity. BMI is inversely proportional to the square of height, therefore even small changes in height can have a large effect on BMI.
BMI, on average, will increase by 1.5kg/m² for men and by 2.5kg/m² for women from age 20 to age 80 independent of any weight change
Height is not the only aspect of body composition that changes with age. Lean body mass is lost as well. Simple adjustment of the observed BMI for height loss will not make BMI an age-invariant measure.

Funding Source:

Government:	National Institute on Aging
University/Hospital:	University of Maryland School of Medicine

Reviewer Comments:

Results cannot be generalized to racial/ethnic groups other than non-Hispanic white.

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?	???
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.)	Yes
	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?		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?	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?	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)?	???
	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