EAL

DLM: Homocysteine, Folate, B6 or B12 (2007-2011)

Citation:

Weng LC, Yeh WT, Bai CH, Chen HJ, Chuang SY, Chang HY, Lin BF, Chen KJ, Pan WH. Is ischemic stroke risk related to folate status or other nutrients correlated with folate intake. Stroke. 2008. 39:3152-8.

PubMed ID: 18988909

Study Design:

Retrospective cohort study

Class:

B - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

To determine the association of dietary or plasma folate with ischemic stroke (IS) incidence and to identify nutrient patterns associated with folate intake and IS risk in Taiwan.

Inclusion Criteria:

Adults in the CardioVacular Disease risk FACtor Two-township study in Taiwan (CVD-FACTS) over 40 years old with a total energy intake range between 500-5500 kcal/day for women who had baseline food frequency data (n=6314).

persons were in the Chu-Dong and Pu-tzu township

Exclusion Criteria:

persons under 40 years old, with history of cancer, stroke which may have changed their dietary intake habits (n=84), and people who had missing values for Food Frequency Questionaire (N=613), for other variables (n=797), or was lost of follow-up (n=11). Persons were excluded for extreme dietary intake data (n=5)

Description of Study Protocol:

Recruitment: Nov. 1990-Sept. 1993

Design: Retrospective cohort study

Dietary Intake/Dietary Assessment Methodology: Food Frequency Questionnaire (FFQ) included 49 items of 8 food groups. Nutrient intakes were adjusted by the residual method.

Blinding used: investigators and laboratory staff were blinded to disease status

Intervention: N/A

Statistical Analysis: baseline characteristics for event and non-event groups were compared by t-tests for continuous variables and by Chi-square test for categorical variables.

Cox proporitional hazard model to examine relationship between incidence of IS and levels of folate, plasma folate concentration, other dietary nutrients and dietary factor scores.

Two models were used in the study to adjust other CVD risk factors. Model 1 adjusted for age, sex, age–sex interaction, and model 2 additionally adjusted for area, drinking habit, smoking habit, sex–smoking habit interaction, hypertension, diabetes mellitus, taking hypertensive drugs, BMI, self-report heart disease, central obesity, physical activity, hypertriglyceridemia, hypercholesterolemia, plasminogen, apolipoprotein B, and fibrinogen. Factor analysis (principal component) was used to identify how dietary levels of 22 nutrients were related to one another and fallen into smaller number of factors. All nutrient intake levels had been calorie-adjusted by residual method and then normalized. Varimax rotation was used to separate dietary nutrients into orthogonal dietary factors. Factor score was calculated by summing up intakes of nutrients weighted by their factor loading if the factor loading was greater than 0.45. SAS version 9.1 (SAS institute).

Data Collection Summary:

Timing of Measurements: baseline = Nov. 1990 to sept. 1993. cycles of data collection = 1994-1997, 1997-1999, 2000-2002.

Dependent Variables:

Ischaemic stroke (IS) self-reported and cross-checked by medical records or death certificate.
Fibrinogen and plasminogen from citrated fasting plamsa (after 8h fast) with ACL 300 Plus Automat Clotting and Fibrinolyzing Analysis System. Lipoprotein A and B by nephelometric immunoassay with automated assay Array Protein System. fasting plasma glucose, cholesterol, triglyceride by Monarch 2000 Autoanalyzer. Plasma folate concentration by competitive immunoassay.
Weight, height, waist circumference, Body mass index (BMI). Three times blood pressure was measured after sitting for 5 minutes, and the mean of the last 2 readings was used for analysis. Questionnaire including demographic data (birth date and sex), lifestyle (smoking, alcohol consumption, physical activity), and self-reported health conditions (disease status and drug using record) were also collected.

Independent Variables

Stroke event occurring before 1996 was self-reported and crosschecked by medical records or death certificate. Three sources of information were used to determine the first-ever IS status and the onset time after 1996, including death certificate data, insurance claim records of the National Health Insurance (NHI) database, and
subject’s self-reported disease history. 99.5% of studied subjects were covered by NHI. A first-ever stroke was
defined by any one of the following conditions with codes 430 to 438 from International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM): (1) hospitalization claim for > one day, or (2) more than 3 consecutive outpatient visits to hospitals, followed either by claims for various neurological imaging technology (computed tomography, MRI, transcranial or carotid Doppler sonography) and long-term prescriptions used for IS or by claims for rehabilitation and the long-term IS prescriptions. An unpublished validation study showed that sensitivity and specificity for the above rules were 100% and 95%, respectively; using data from 508 ischemic stroke patients of a hospital-based case-control study.

Control Variables: Model 1: age, sex, age–sex interaction, and model 2 additionally adjusted for area, drinking habit, smoking habit, sex–smoking habit interaction, hypertension, diabetes mellitus, taking hypertensive drugs, BMI, self-report heart disease, central obesity, physical activity, hypertriglyceridemia, hypercholesterolemia, plasminogen, apolipoprotein B, and fibrinogen.

Description of Actual Data Sample:

Initial N: 6314(e.g., 731 (298 males, 433 females))

Attrition : n = 1772 for dietary studies and n = 1687 for plasma studies

Age: over 40

Ethnicity: Taiwan

Other relevant demographics: At baseline, there who developed IS were more with hypertension,DM, self-reported heart disease, large BMI, central obesityat baseline than in those free of stroke, and theevent group had lower level of dietary folate, but higher levelsof age, waist circumference, BMI, serum triacylglycerol concentration,apolipoprotein B, and plasminogen than the nonevent group.

Anthropometrics:

Table 1. Baseline Characteristics of IS Event Group and Nonevent Group

	Nonevent Group (n=1640)	IS Event Group (n=132)	P Value
Mean age, y	56.1 (9.8)	62.6 (8.1)	<0.001
Sex, %
Male	43.7	49.2	0.639
Female	56.3	50.8
Area, %
Chu-Dong	54.4	52.3	0.214
Pu-Tzu	45.6	47.7
Dietary Folate, µg/d^*	397.1 (170.4)	364.0 (176.8)	0.032
Smoking habits, %
Never	77.8	70.5	0.148
Past	3.1	4.6
Current	19.1	25.0
Alcohol consumption habits, %
Never	91.0	90.2	0.815
Past	0.18
Current	8.8	9.9
Hypertension, %
Yes	21.5	40.9	<0.001
No	78.5	59.1
Diabetes mellitus, %
Yes	9.5	23.5	<0.001
No	90.6	76.5
Self-report heart disease, %
Yes	3.9	8.3	0.015
No	96.1	91.7
Physical activity, %
Yes	41.4	47.0	0.212
No	58.6	53.0
Mean BMI, kg/m²	24.4 (3.3)	25.3 (3.4)	0.002
BMI level, %
Normal: $≤$ 24	48.5	34.9	0.009
Overweight: 24–27	31.7	41.7
Obesity: $≥$ 27	19.8	23.5
Waist circumference, cm	81.2 (9.5)	85.1 (9.5)	<0.001
Central obesity, %^\|\|	36.2	49.2	0.003
Mean serum cholesterol concentration, mg/dL	202.0 (41.5)	207.2 (42.2)	0.167
Hypercholesterolemia, %^#
Yes	16.7	22.0	0.118
No	83.4	78.0
Mean serum triacylglycerol concentration, mg/dL	108.8 (73.3)	136.4 (85.1)	<0.001
Hypertriglyceridemia, %^**
Yes	8.7	16.7	0.003
No	91.3	83.3
Mean fibrinogen concentration, mg/dL	280.5 (76.5)	287.0 (75.4)	0.341
Apolipoprotein B, mg/dL	114.9 (31.7)	121.5 (30.3)	0.022
Plasminogen, %	122.7 (34.0)	131.3 (40.1)	0.018
(Continued)

Location: Taiwan. Five villages with more than 1000 people and with population density greater than 200 people per square kilometer randomly selected from Chu-Dong township (northwest Taiwan) and Pu-Tzu township (southwest Taiwan).

Summary of Results:

An inverse association was observed between folate intake andIS (Table 2) after adjusting for age, sex, and age–sexinteraction.

Table 2. Hazard Ratios and 95% CIs for Incident IS Event by Quartiles of Folate Status

	Quartiles of Folate			P for Trend^*
	Q4+Q3 High	Q2	Q1 Low	P for Trend^*
Dietary level, µg/d	<369.45	297.33–369.45	<297.33
Event/n	50/886	44/443	38/443
Model 1	1	1.77 (1.18–2.67)	1.46 (0.95–2.26)	0.034
Model 2	1	1.83 (1.21–2.78)	1.59 (1.02–2.47)	0.014
Plasma concentration, ng/mL	>7.77	5.88–7.77	<5.88
Event/n	62/843	31/422	34/422
Model 1	1	1.00 (0.65–1.56)	0.91 (0.58–1.42)	0.736
Model 2	1	0.90 (0.57–1.42)	0.78 (0.49–1.25)	0.323

*P for trend based on the 3-group data (Q1, Q2, and Q3+Q4).
${dagger}$ Dietary folate was calorie-adjusted.
${ddagger}$ No. of people at risk in the category.
Model 1 was adjusted for age (40–50, 50–60, 60–70, $≥$ 70), sex, age*sex.
Model 2 was adjusted for the covariates in model 1 plus hypertension (yes, no), use of antihypertensive drugs (yes, no), diabetes mellitus (yes, no), area (Chu-Dong and Pu-Tzu), central obesity (yes, no), alcohol consumption habits (never, ex-drinker, current drinker), smoking habit (never, ex-smoker, current smoker), sex-smoking habit interaction, BMI ( $≤$ 24, 24–27, $≥$ 27 kg/m²), self-report heart disease (yes, no), hypercholesterolemia (yes, no), hypertriglyceridemia (yes, no), physical activity (yes, no), fibrinogen (tertiles), apolipoprotein B (tertiles), and plasminogen (tertiles).

Author Conclusion:

The authors concluded: Dietary folate was an independently protective factor of IS,whereas plasma folate was not associated with the risk of ISin this Taiwanese population where people have relatively higherlevels of plasma folate concentration than those of previousliterature and intracranial diseases are more prevalent comparedto Western countries. More significant was the inverse associationbetween risk of IS and some other nutrients correlated withdietary folate, including vitamin B2, potassium, iron, vitaminA of plant origin, or calcium. This inverse association mayin part be compounded by other nutrients or food componentsin plant foods. Cautions are needed to make conclusion fromobservational nutrition epidemiological studies."

Reviewer Comments:

The authors stated the following limitations:

length of blood samplestorage and the potential that subjects may have modified their dietarybehaviors during the follow-up period. In previous studies,the concentration of plasma folate decreased obviously afterlong-time storage at –20°C.⁴¹ However, authors note that samples were stored at–70°C, and the correlation between plasmafolate and homocysteine concentration in the study was significant(r=–0.20, P<0.0001) after storing over 11 years, indicatingthat the concentration of plasma folate was reliable.
During the 10.6 years of follow-up, subjects in the study mayhave changed their diets. However, we have documented a positivefinding.

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)	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?	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)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	No
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	Yes
	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?	Yes
	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?	Yes
	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?	???
	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?	Yes
	6.6.	Were extra or unplanned treatments described?	Yes
	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?	???
	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?	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?	No
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