EAL

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

Citation:

Virtanen JK, Voutilainen S, Happonen P, Alfthan G, Kaikkonen J, Mursu J, Rissanen TH, Kaplan GA, Korhonen MJ, Sivenius J, Salonen JT. Serum homocysteine, folate and risk of stroke: Kuopio Ischaemic Heart Disease Risk Factor Study. Eur J Cardiovasc Prev Rehabil 2005; 12(4):369-375.

PubMed ID: 16079645

Study Design:

Prospective Cohort Study

Class:

B - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

The purpose of this study is to examine the effects of serum homocysteine and folate levels on the risk of stroke (including all stroke and ischaemic stroke) in middle-aged men in eastern Finland.

Inclusion Criteria:

middle-aged men from eastern Finland (no additional details published in this paper)
aged 42, 48, 54, or 60 during enrollment for the study (between 1984 and 1989)

Exclusion Criteria:

death or severe illness during follow-up
migration from region during follow-up
lack of contact information/refusal to participate during follow-up
men with history of stroke

Description of Study Protocol:

Recruitment: the Kuopio Ischaemic Heart Disease Risk Factor (KIHD) Study is an ongoing prospective population based cohort study designed to investigate risk factors for CVD, atheroscletosis and related outcomes in middle -aged men from eastern Findland.

Design: The baseline exam for this analysis was conducted during 1991-1993 (during the 4-year reexamination for the study) to determine serum homocysteine (tHcy) and folate status. Data on participants' medical history, smoking, alcohol consumption, blood pressure, physical activity in leisure time, and BMI was also collected. Incidence of stroke was collected through December 2002 using the national stroke register, national hospital discharge registry, and death certificate registry.

Dietary Intake/Dietary Assessment Methodology: Alcohol consumption was determined through interviews and questionnaires (no details provided). No other dietary data collected.

Blinding used: N/A

Intervention : N/A

Statistical Analysis: The data is expressed as mean + standard deviation (means compared with ANOVA). Categorical variables were compared with the chi-square test. Correlations were estimated with Pearson correlation coefficients. The associations between serum tHcy or folate and risk of stroke were analyzed using Cox proportional hazards models. Adjusted hazard rate ratios (RR) were estimated as the antilogarithms of coefficients from multivariable models. Confounders included:

systolic blood pressure
smoking
diabetes
body mass index
serum total and low-density lipoprotein cholesterol
alcohol intake
history of ischaemic heart disease
income
total physical activity

Confounding factors were eliminated from the full model if their joint removal did not change the tHcy by 10% or more.

Data Collection Summary:

Timing of Measurements: Baseline data for this study was collected between 1991-1993. Follow-up was conduced through December 2002 (mean follow-up time of 9.6 years).

Dependent Variables:

Stroke incidence (diagnosed based on ICD-9 codes 430-439 and ICD-10 codes I60-I68 and G45-G46). Each stroke was classifed as either an ischaemic stroke or hemorrhagic stroke. (If the subject had multiple strokes during follw-up, the first event was considered the end point).

Independent Variables: serum tHcy and serum folate levels

Control Variables:

systolic blood pressure
smoking
diabetes
body mass index
serum total and low-density lipoprotein cholesterol
alcohol intake
history of ischaemic heart disease
income
total physical activity

Description of Actual Data Sample:

Initial N: Out of 2682, 1229 men were elegible for the study. also, 52 died, had had a severe illness, or had migrated from the region, 139 refused to participated . Finaly, these men were examinated in 1991-1993.

Attrition (final N): final n=1015 males

Age: age at enrollment 42, 48, 54, or 60 during enrollment for the study (between 1984-1989)

Ethnicity: not specified

Other relevant demographics: not specified

Anthropometrics: According to the data on baseline characteristics of study participants based on tertiles of serum tHcy concentration, the only significant differences (p<0.001) were found with age and serum folate levels. According to the data on baseline characteristics of study participants based on tertiles of serum folate concentration, significant differences (p<0.001) were found with serum tHcy levels, diastolic blood pressure, alcohol consumption, and diabetes.

Location: eastern Finland

Summary of Results:

Elevated serum tHcy seems to be associated with increased risk of all strokes and ischaemic strokes, while elevated serum folate concentrations appear to protect against incident strokes.

Table 1: Age and exam year-adjusted risk ratios for stroke based on tertiles of serum tHcy concentration

		Risk Ratio (95% CI)		P trend
	<9.6 µmol/L	9.6-11.4 µmol/L	>11.4 µmol/L
All strokes	1	2.16 (0.94-4.96)	2.77 (1.23-6.24)	0.0014
Ischaemic strokes	1	1.71 (0.63-4.64)	2.61 (1.02-6.71)	0.039

* no changes observed with additional adjustment for confounding factors

Table 2: Age and exam year-adjusted risk ratios for stroke based on tertiles of serum folate concentration

		Risk Ratio (95% CI)		P trend
	<8.2 nmol/L	8.2-11.2 nmol/L	>11.2 nmol/L
All strokes	1	1.04 (0.57-1.9)	0.43 (0.18-1.05)	0.200
Adjusted all strokes*	1	1.00 (0.55-1.83)	0.35 (0.14-0.87)	0.046
Ischaemic strokes	1	0.81 (0.38-1.72)	0.49 (0.18-1.31)	0.361
Adjusted ischaemic strokes**	1	0.79 (0.37-1.68)	0.40 (0.15-1.09)	0.117

* Adjusted for alcohol intake and diabetes

** Adjusted for serum LC cholesterol and diabetes

Table 3: Hazard rate ratios for all strokes stratified by serum tHcy and serum folate

		Unadjusted*		Adjusted**		Number of cases
		RR (95% CI)	P	RR (95% CI)	P
tHcy (µmol/L)	Folate (nmol/L)
< 10.4	>9.6	1	--	1	--	12
< 10.4	< 9.6	0.84 (0.33-2.13)	0.709	0.98 (0.38-2.53)	0.973	7
>104	>9.6	0.90 (0.37-2.22)	0.819	0.83 (0.34-2.06)	0.690	8
>10.4	<9.6	1.78 (0.87-3.65)	0.114	2.08 (1.01-4.31)	0.048	22

* Adjusted for age and exam year

** Adjusted for age, exam year, alcohol intake, and diabetes

Table 4: Hazard rate ratios for ischaemic strokes stratified by serum tHcy and serum folate

		Unadjusted*		Adjusted**		Number of cases
		RR (95% CI)	P	RR (95% CI)	P
tHcy (µmol/L)	Folate (nmol/L)
< 10.4	>9.6	1	--	1	--	7
< 10.4	< 9.6	0.82 (0.24-2.82)	0.757	0.96 (0.28-3.32)	0.951	4
>104	>9.6	1.33 (0.46-3.82)	0.595	1.29 (0.45-3.70)	0.637	7
>10.4	<9.6	2.16 (0.88-5.34)	0.094	2.46 (0.99-6.10)	0.052	16

* Adjusted for age and exam year

** Adjusted for age, exam year, serum LDL cholesterol, and diabetes

Author Conclusion:

Results indicate that higher serum tHcy concentrations may increase the risk of stroke while high serum folate concentrations may be protective against stroke in a population of middle-aged Finnish men with no prior history of stroke.

Reviewer Comments:

No dietary data collected-other dietary factors could act as confounders of this data.

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?	???
	2.4.	Were the subjects/patients a representative sample of the relevant population?	No
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?	???
	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?	N/A
	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?	No
	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?	N/A
	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?	N/A
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	N/A
	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?	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