EAL

UWL: Association With Outcomes (2009)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To examine the natural history of weight loss in patients with Parkinson's disease and its relation to energy intake.

Inclusion Criteria:

Study population included male health professionals from the Health Professionals Follow-up Study and registered nurses from the Nurses' Health Study, who provided detailed information on their medical history and lifestyle practices.

Exclusion Criteria:

Investigation restricted to men and women who provided baseline information on their weights or dietary habits, and who were free of Parkinson's disease, stroke or cancer (other than nonmelanoma skin cancer) at that time.

Description of Study Protocol:

Recruitment

Data from two large prospective cohorts of men and women with repeated measurements on weight and energy intake (the Health Professionals Follow-up Study, 1986 to 2000, and the Nurses' Health Study, 1976 to 1998).

Design

Prospective cohort study.

Statistical Analysis

Overall results of men and women are presented since the findings are similar across gender
Mean weight changes were plotted according to the time from diagnosis
To account for age and secular-related weight changes, the weight reported by all cohort participants were regressed on age, age squared and height for each time period
A similar approach was used to derive energy intake residuals with adjustment for age and time period
Generalized estimating equation models were used to test for the statistical significance of the changes of weight or energy intake over time
Relative risks were calculated using the Cox proportional hazards models adjusting for age, smoking status, alcohol intake and caffeine consumption.

Data Collection Summary:

Timing of Measurements

Data from the Health Professionals Follow-up Study (HPFS), 1986 to 2000, and the Nurses' Health Study (NHS), 1976 to 1998
Participants were followed up with biennial questionnaires to update information on potential risk factors for and the occurrences of major chronic diseases
Food frequency questionnaires were administered in the HPFS in 1986, 1990, 1994 and 1998 and in the NHS in 1980, 1984, 1986, 1990 and 1994
The end of the follow-up was January 31, 2000 for males and May 31, 1998 for females.

Dependent Variables

Weight change: Participants asked to report their current weight in 1986 for males and 1976 for females
Energy intake: Dietary information first collected in 1986 for males and 1980 for females through the use of food frequency questionnaires.

Independent Variables

Parkinson's disease: A specific question on lifetime Parkinson's disease occurrence was first asked in 1988 for males and in 1994 for females, and a question on Parkinson's disease diagnosis within the previous two years was asked in subsequent surveys
Diagnosis was confirmed by the treating neurologist.

Control Variables

Age
Smoking status
Alcohol intake
Caffeine consumption.

Description of Actual Data Sample:

Initial N: 51,529 male health professionals and 121,700 female registered nurses
Attrition (final N): 468 individuals with Parkinson's disease (267 males and 201 females). 174 (96 males and 78 females) reported their weights around the time of diagnosis and were included in the weight change analyses.

Age

Male health professionals, aged 40 to 75 years
Female registered nurses, aged 30 to 55 years.

Location

United States.

Summary of Results:

Other Findings

The average weight of patients with Parkinson's disease was stable until shortly before the diagnosis (P=0.2) and then declined thereafter (P<0.0001)
There was a clear trend of weight loss over the observational period (P<0.005)
The average weight loss was 5.2 lb in the 10 years before the diagnosis and 7.7 lb in the eight years after the diagnosis
On average, Parkinson's disease patients lost 8.5 lb more than participants without Parkinson's disease, and most of the loss (5.0 lb) occurred in the four years preceding diagnosis
Parkinson's disease patients tended to increase their energy intakes as their weights decreased (P<0.002)
Compared with non-cases, the average increment in energy intake starting from two to four years before the diagnosis was 347kcal among Parkinson's disease patients.

Author Conclusion:

In summary, we found in this prospective study that patients with Parkinson's disease began to lose weight several years before the disease was diagnosed, despite an increased energy intake, suggesting that energy expenditure increases early in the course of Parkinson's disease. Further investigations are needed to assess whether this increase in energy expenditure is explained by early symptoms of the disease or whether it results from an underlying metabolic defect in patients with Parkinson's disease.

Funding Source:

Government:

NIH

Not-for-profit

Kinetics Foundation

Other non-profit:

Reviewer Comments:

Cohorts represented health professionals and nurses. Weight was based on self-report. Energy expenditure was noted as contributing to weight loss, but cohort data on physical activity was not included.

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?		???
	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?	N/A
	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?		N/A
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	N/A
	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?		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?	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?		???
	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?	No
	7.5.	Was the measurement of effect at an appropriate level of precision?	???
	7.6.	Were other factors accounted for (measured) that could affect outcomes?	No
	7.7.	Were the measurements conducted consistently across groups?	N/A
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?	???
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