and 155-161
Folic Acid Levels in Acute Cerebral Infarction
Tohoku J. Exp. Med., 2004,B12204,
155
Serum Vitamin B12 and Folic Acid Levels in Acute
Cerebral Atherothrombotic Infarction
ABDULKADIR KOCER, NURHAN INCE,1 E. CUNEYT CANBULAT2 and MEHMET SARGIN3
Department of Neurology, Dr. Lutfi Kirdar Kartal Education and Research
Hospital, 1Department of Public Health, Istanbul Medical Faculty, University of
Istanbul, 2Department of Clinical Biochemistry, PTT Education and Research
Hospital, and 3Department of Family Medicine, Dr. Lutfi Kirdar Kartal
Education and Research Hospital, Istanbul, Turkey
KOCER, A., INCE, N., CANBULAT, E.C. and SARGIN, M. Serum Vitamin B12 and
Folic Acid Levels in Acute Cerebral Atherothrombotic Infarction. Tohoku J. Exp.
Med., 2004, 204 (2), 155-161 ── Hyperhomocysteinemia is an independent risk
factor for atherothrombotic cerebral stroke. Vitamin B12 and folic acid are important
determinants of homocysteine metabolism. We aimed to evaluate the relationship, if
present, between vitamin B12 and folic acid levels and acute cerebral stroke in this
study. Blood aliquots drawn within 24 hours after the stroke from hospitalized patients (n=66) with the diagnosis of acute ischemic cerebrovascular episode and also
blood samples from 38 healthy controls without any vascular risk factor were analyzed. With a competitive, chemoluminescence assay, serum levels of vitamin B12
and folic acid were measured in blood samples taken within 24 hours after the stroke.
The differences and correlations were tested using frequency test, student-t test and
multivariate analysis. Mean serum vitamin B12 levels were significantly lower in the
patients than in the control subjects, 245.40 (S.D.: 72.9) and 343.2 (S.D.: 113.0) pg/ml
respectively (p=0.0001). This difference was independent from other risk factors.
Likewise, mean serum folic acid levels were lower in the patients than in the control
subjects, 4.62 (S.D.: 1.94) and 5.97 (S.D.: 1.19) ng/ml, respectively (p=0.003). Mean
serum levels of vitamin B12 and folate at the convalescence phase were 253.05 (S.D.:
68.78) pg/ml and 4.48 (S.D.: 2.08) ng/ml, respectively; the values obtained at the
acute phase were not significantly different from the values obtained at the convalescence phase. We conclude that low vitamin B12 and folic acid concentrations are associated with an increased risk of stroke, and the relationship for vitamin B12 is independent from the other known modifiable stroke risk factors. For understanding the
effects of B12 and folate in stroke patients, more detailed follow-up studies with long
period are needed. ──── hyperhomocysteinemia; B12; folate; atherotrombosis;
stroke
© 2004 Tohoku University Medical Press
Received March 30, 2004; revision accepted for publication August 9, 2004.
Address for reprints: Kocer Abdulkadir, M.D., Chief Assistant, Department of Neurology, Dr. Lutfi Kirdar
Teaching and Research Hospital, Istanbul, Turkey.
e-mail: abdulkadirkocer@yahoo.com
This article was partially presented as poster (Poster Number 3 at 18 May 2004) at International Congress Of
Neuromediterranee VI, 17-21 May 2004, Istanbul, Turkey.
155
156
A. Kocer et al.
Hyperhomocysteinemia (HH) has been observed in arterial and venous thrombotic diseases.
Even mild or moderate degrees of increments are
known to increase the risk of vasooclussive diseases (Fortin and Genest 1995; Saw 1999; Robins
et al. 2001; Yilmaz et al. 2001). During metabolization of homocysteine, vitamin B6, folic acid
and vitamin B12 are required. Deficiencies of vitamin B6, folic acid and vitamin B12 lead to the interruption of metabolic pathways, and homocysteine rapidly escapes from tissues (Brattstrom et al.
1992; Robinson et al. 1998). The role of HH in
the pathogenesis of atherothrombosis has not been
fully elucidated. HH is known to lead to the production of free oxygen radicals. It also stimulates
the development of smooth muscles and inhibits
intracellular methylation processes (Tsai et al.
1996; Dalton et al. 1997; Engman 1998; Selhub
and D’Angelo 1998). HH alters anticoagulation
pathways within endothelium via inhibition of
thrombomodulin formation as well (Engman
1998; Selhub and D’Angelo 1998; Saw 1999).
Studies evaluating both an established threshold
value for vitamins and also investigating whether
HH is the only factor enhancing atherothrombotic
predisposition in B6, B12 and folate deficiency will
certainly lead to important outcomes regarding
preventive medicine (Engman 1998; Robinson et
al. 1998; Saw 1999; Robins et al. 2001; He et al.
2004). Besides methodological difficulties, homocysteine assays are relatively costly and they
have not come into routine usage.
In this study, we evaluated the effects of vitamin B12 and folate levels on acute cerebrovascular stroke, which is an important cause of morbidity and mortality worldwide. The present study
searched for an answer to an issue: “Is deficiency
of vitamin B12 or folic acid a responsible risk factor predisposing to atherothrombosis ? .”
MATERIAL AND METHODS
Study design and setting
In this study, blood samples were drawn
within 24 hours after the stroke from hospitalized
patients (n=66) with the diagnosis of acute cere-
brovascular episode in PTT Training and Research
Hospital -related to PTT establishment serving
post, telephone and telegraph services in Turkey
and PTT word contains the first letters of Post,
Telephone, and Telegraph words-, Istanbul,
Turkey and also blood samples from 38 similarly
age- and sex-matched healthy control subjects
without any vascular risk factors were analyzed.
After at least one month, we had blood analysis of
vitamins of patients in order to compare with
acute phase results. Before each analysis, the objective of the study was described and informed
consent was obtained from all patients.
Definition of stroke and modifiable risk factors
The diagnosis of stroke was made by a neurologist according to the criteria of World Health
Organization defining stroke as rapidly developing clinical symptoms lasting more than 24 hours
or leading to death without any other etiology
other than a vascular abnormality (Hatano 1976).
The following criteria were used for the diagnosis
of stroke: clinical evidence of stroke and computed tomography (CT) evidence of cerebral infarction without demonstrable source of embolism.
Patients were evaluated with cranial CT (n=54)
and cranial magnetic resonance imaging (MRI)
(n=25) to define stroke, and were grouped as anterior and posterior system infarctions. Lacunars
infarcts without large artery thrombosis, thromboembolic infarcts and hemorrhagic infarcts were
not included in this study. We did not include
people with a history of vitamin complex tablets
intake within last three months. The modifiable
risk factors were noted. Hypertension was considered to be present if at the time of diagnosis the
subjects had a systolic blood pressure >160
mmHg or a diastolic pressure >95 mmHg, and if
treatment for high blood pressure was administered previously. Hypercholesterolemia was considered present if subjects had serum total cholesterol >200 mg/100 ml. Hyperglycemia was
considered present if subjects had a serum glucose
level >115 mg/100 ml, or if treatment for diabetes
was started previously.
B12 and Folic Acid Levels in Acute Cerebral Infarction
Laboratory analysis
Routine hematological, biochemical and microbiologic analyses (blood glucose, urea, creatinine, total lipid, triglyceride, cholesterol, lipoproteins, creatinine phosphokinase, AST, ALT,
bleeding, coagulation, prothrombine and partial
prothrombine times) were performed. With a
competitive, chemoluminescence assay using
Immulite 2000 (DPC, Los Angeles, CA, USA)
analyzer, serum levels of vitamin B12 and folic
acid were measured in blood samples taken within
24 hours after the stroke.
Statistical Analysis
Intergroup differences and correlations were
tested using frequency test, student t-test and multiple logistic regression. Data were expressed as
mean and Standard Deviation (S.D.) in brackets.
All analyses were made using the SPSS 10.0 version statistical software package, and probability
value of less than 0.05 was accepted to be statistically significant.
RESULTS
The study group consisted of 66 patients and
38 control subjects with similar distribution of
gender and age. Descriptive features of patients
are shown in Table 1. Mean ages of female and
157
male patients were 67.6 (S.D.: 9.9 years, R: 50-89)
and 61.5 (S.D.: 11.5 years, R: 44-85), respectively.
The average stay in hospital was 11.9 (S.D.: 6.15)
days. The correlations between serum levels of
B12 and patients’ ages were found to be statistically significant (p=0.0001). The correlations between serum levels of folate and patients’ ages
were not significant (p=0.286). The correlations
between serum levels of B12, folate and controls’
ages were not found to be statistically significant
(p=0.062 for B12, and p=0.70 for folate). When
cohort of patients was evaluated, mean B12 values
were detected to be 283.6 (S.D.: 82.1) pg/ml for
females and 207.13(S.D.: 32.6) pg/ml for males;
the difference was significant (p=0.0001). There
was no relation between gender and mean
folate levels in the patient group (males: 4.59 [S.D.:
1.47], female: 4.66 [S.D.: 2.39], p=0.902).
As seen on Table 1, mean serum levels of vitamin B12 were significantly lower in the patient
group than in the control group: 245.4 (S.D.: 72.9)
and 343.2 ( S . D .: 113.0) pg/ml, respectively
(p=0.0001). Mean serum folic acid levels of patients were lower than those of control subjects as
well (4.62 s.d.: 1.94 and 5.97 S.D.: 1.19 ng/ml, respectively) and the difference was statistically
significant (p=0.003). Mean serum levels of vitamin B12 (253.05 [S.D.: 68.78] pg/ml) and folate
TABLE 1. Descriptive characteristics of patients and control group
Case (n)
Gender
Male
Female
Mean age (years)
Patients
Controls
66
34 (%51.5)
32 (%48.5)
64.46 (11.10)
38
20 (%52.6)
18 (%47.4)
60.28 (12.96)
p value
0.931
0.085
Serum B12 level
(pg/ml)
*
N: 174-878 pg/ml
Mean±S.D.
Median
245.4 (72.9)
235 (R: 160-479)
343.2 (113.0)
329 (R: 203-635)
0.0001
Serum folate level
(ng/ml)
*
N: 3-17 ng/ml
Mean±S.D.
Median
4.62 (1.94)
4.96 (R: 1.51-9.20)
5.97 (1.19)
5.54 (R: 4.0-7.51)
0.003
*
Our Lab’s reference ranges.
158
A. Kocer et al.
(4.48 [ S . D .: 2.08] ng/ml) at the convalescence
phase were not significantly different from the
acute phase values.
B12 values were unrelated to the presence of
vascular risk factors. As it was seen in Table 2,
the multivariate analysis showed that the odd’s ratio was 1.02 for B 12 (95% CI, 1.005-1.040;
p=0.013). When cases with cerebrovascular
events were classified according to the localization of the damage (anterior or posterior systems),
mean values of vitamin B12 were found to be lower (230.35 [S . D .: 51.59] pg/ml) in the patients
whose both systems involved than in the patients
with anterior or posterior circulation problems
(254.88 [S.D.: 83.07] pg/ml) (p=0.68). Mean folate levels were detected to be lower in cases with
anterior or posterior circulation involvement than
in the ones with involvement of both anterior and
posterior circulations (4.39 [S.D.: 2.09] versus 5.17
[S.D.: 1.47]); but the difference was not statistically significant. The previous stroke history was
present in 20 (30.3%) and cardiac disorder was
present in 21 (31.8%) of the patients. The presence of cardiac disease in cases with stroke influenced vitamin B12 levels, which were significantly
decreased (p=0.002). The presence of previous
stroke history in patients did not influence vitamin
B12 and folate levels.
DISCUSSION
HH is suggested to be an independent risk
factor for atherosclerotic cerebrovascular diseases
aside from classical vascular risk factors such as
hypertension, smoking, hyperlipidemia, hyperglycemia and hyperfibrinogenemia (Brattstrom et al.
1992; Giles et al. 1998; Robinson et al. 1998;
Sacco et al. 1998). HH exerts unfavorable effects
on coagulation factors and platelets. A linear correlation has been demonstrated between peripheral vascular disease and homocysteine metabolism
(Selhub and D’Angelo 1998). A negative correlation exists between serum homocysteine metabolites (vitamin B12, folate) and homocysteine levels. Decreases in circulating vitamin B12 and
folate levels reveal an increase in the risk of atherothrombosis (Verhof et al. 1996; Robinson et al.
1998; Giles et al. 1998; Siri et al. 1998; He et al.
2004).
A correlation between cardiovascular mortality, morbidity and HH has been demonstrated in a
number of cross-sectional, case-controlled cohort
studies but a range for homocysteine values relevant to the risk of cardiovascular disease has not
been defined yet (Verhof et al. 1996; Verhof et al.
1997; Saw 1999). An analysis of 13 different
studies performed between 1969 and 1998 revealed that HH associated with vitamin B12 and
folate deficiency increases the risk of stroke
(Engman 1998). Although moderate reduction of
total homocysteine after nondisabling cerebral infarction had no effect on vascular outcomes during the 2 years of follow-up, HH was present in
acute and recovery periods of cerebrovascular accidents (Hultberg et al. 1997; Vila et al. 1998;
Meicklejohn et al. 2001; Toole et al. 2004). In
one of the recent studies, Meicklejhon et al. (2001)
TABLE 2. Multivariate analysis of vitamin levels with modifiable risk factors.
Hypertension
Heart disease
Diabetes Mellitus
Cholesterol
LDL Cholesterol
Vitamin B12
Folate
B coefficient
S.E.
Odd’s Ratio
95% CI
Significant (p)
−.559
.899
−.048
−.030
.046
.022
.472
1.151
1.142
.027
.023
.031
.009
.499
0.572
2.457
0.953
0.970
1.047
1.022
1.603
0.060-5.461
0.262-23.04
0.903-1.006
0.928-1.015
0.985-1.113
1.005-1.040
0.603-4.259
0.627
0.431
0.079
0.186
0.140
0.013
0.344
B12 and Folic Acid Levels in Acute Cerebral Infarction
has evaluated the association of HH with episodes
of stroke and reported that in the acute phase, the
incidence of the risk of stroke did not differ from
those of control groups, albeit the level of homocysteine increased in the subsequent phase of
stroke. Hultberg et al. (1997) similarly reported
the presence of HH during the recovery period.
Vila et al. (1998) showed that total plasma homocysteine concentrations were higher in stroke patients compared to controls. Moderate degrees of
HH were present in 20% of their cases. It has
been associated with vitamin B12 decrease, whereas no correlation was found between HH and folate
levels. Verhoef et al. (1996) found a correlation
between lower serum B12 levels and cardiovascular diseases independent of total HH levels. On
the contrary, they have established that low levels
of folate are associated with HH but unrelated to
cardiovascular diseases. In another study, Verhoef
et al. (1997) likewise found an important relationship between low serum vitamin B12 levels and
vascular diseases. In the same study, serum folate
levels were assessed to be increased. Giles et al.
(1995) have shown that folic acid levels below 9.2
nmol/liter predispose to an increase in the risk of
cerebrovascular diseases. Yilmaz et al. (2001)
evaluated serum vitamin B12 and folate levels in
cases of stroke and found statistically significant
correlations among cerebrovascular stroke, serum
BI2 and folate levels. In our study serum levels of
vitamin B12 and folate were lower in the patient
group than in the control group. Like some previous studies, we found that the significance for B12
level was much more prominent when compared
to folate (Table 1). Substantial decreases in vitamin B12 and folate levels in cases with acute cases
of stroke were found when compared with those
of the control group in our study. Multivariate
analysis showed that vitamin B12 level decrease
was an independent factor for acute stroke in the
present study (Table 2). The results of the present
study support the thesis suggesting a correlation
between decrease in vitamin levels and vascular
damage which might result in stroke.
HH becomes more prominent in older age
159
groups and in the presence of the risk factors.
Dalery et al. (1995) found that homocysteine
levels in healthy women were lower than in their
male counterparts. Different studies showed that
HH is a more important risk factor for women in
terms of ischemic stroke (Selhub et al. 2000;
Verhoef 2000). Serum vitamin B12 levels manifesting a negative correlation with homocysteine
were relatively higher in female patients in our
study (p=0.0001). On the other hand, there was
no significant relationship between gender and folate levels in patients although females had higher
levels of folate. These findings were similar to
the literature. Selhub et al. provided reference
ranges for vitamins based on sample by sex and
ethnicity (Selhub et al. 1999) and similar ranges
for vitamin levels were found in the Framingham
study population (Selhub et al. 2000). Although
those results show that our control population had
lower folate level but similar vitamin B12 levels,
our vitamin level results were much lower when
compared to the study conducted by Yilmaz et al.
(2001); that could be explained by different age
groups of study subjects.
The diagnostic usefulness of folate and vitamin B12 measurements were evaluated considering plasma homocysteine in the present study.
We determined vitamin B12 and folate levels because they influence homocysteine concentrations
in plasma but we did not measure plasma homocysteine. This point may be a criticism of the
present study. Considering only folate and vitamin B12, the sample size would not be sufficient
to analyze the predictive value of these two vitamins, especially if there had been a distinct gender difference for vitamin B12. In our study the
groups were well matched, so we were able to
compare the differences of vitamins. Age is a
confounder so that needs to be considered. B12
(but not folate) is decreased with an increasing
age in the present study confirming previous papers (Robins et al. 2001; Dharmarajan et al.
2003). In the convalescent period, blood levels of
vitamins showed decreased values, too. This supports that decrease in vitamin levels may be a risk
160
A. Kocer et al.
factor for atherothrombotic stroke, though Yilmaz
et al. (2001) found decreased levels of vitamins in
both ischemic and hemorrhagic strokes and
claimed that acute phase variations were also
likely to effect the serum levels of those vitamins.
We concluded that the assessment of serum levels
of vitamin B12 and folate levels on acute cerebrovascular stroke was important for definition of
risk factors. We think timely screening and replacement of vitamin B12 will help to prevent future stroke events. Although the present study
may be thought as a small study with inadequate
matching of cases and controls, this study is important with a good selection of groups, because
the patients or cases with vitamin usage history,
patients with a thromboembolic stroke, patients
with pernicious anemia which also increases with
age, and patients administered to hospital after 24
hours of stroke were not included.
References
Brattstrom, L., Lindgren, A., Israelsson, B., Malinow,
M.R., Norrving, B., Upson, B. & Hamfelt, A.
(1992) Hyperhomocysteinaemia in stroke:
prevalence, cause, and relationships to type of
stroke and stroke risk factors. Eur. J. Clin. Invest., 22, 214-221.
Dalery, K., Lusier-Cacan, S., Selhub, J., Davignon, J.,
Latour, Y. & Genest, J. (1995) Homocysteine
and coronary artery disease in French Canadian
subjects: relation With vitamins B12, B6, pyridoxal phosphate, and folate. Am. J. Cardiol.,
75, 1107-1111.
Dalton, M.L., Gadson, P.J., Wrenn, J. & Rosenquist,
T.H. (1997) Homocysteine signal cascade: Production of phospholipids, activation of protein
kinase C, and the induction of c-fos and c-mybin smooth muscle cells. FASEB. J., 11,
703-711.
Dharmarajan, T.S., Adiga, G.U. & Norkus, E.P. (2003)
Vitamin B12 deficiency. Recognizing subtle
symptoms in older adults. Geriatrics, 58,
30-34.
Engman, M. (1998) Homocysteinemia: new information about an old risk factor for vascular disease. J. Insur. Med., 30, 231-236.
Fortin, L.J. & Genest, J. (1995) Measurement of
homocyst(e)ine in prediction of arteriosclerosis.
Clin. Biochem., 28, 155-162.
Giles, W.H., Kittner, S.J., Anda, R.F., Croft, J.B. &
Casper, M.I. (1995) Serum folate and risk for
ischemic stroke. First National Health and Nutrition Examination Survey epidemiologic follow-up study. Stroke, 26, 1166-1170.
Giles, W.H., Croft, J.B., Greenlund, K.J., Ford, E.S. &
Kittner, S.J. (1998) Total homocyst(e)ine concentration and the likelihood of nonfatal stroke:
results from the Third National Health and Nutrition Examination Survey, 1988-1994. Stroke,
29, 2473-2477.
Hatano, S. (1976) Experience from a multicentre
stroke register: a preliminary report. Bull.
World Health Organ., 54, 541-553.
He, K., Merchant, A., Rimm, E.B., Rosner, B.A.,
Stampfer, M.J., Willett, W.C. & Ascherio, A.
(2004) Folate, vitamin B6, and B12 intakes in
relation to risk of stroke among men. Stroke,
35, 169-174.
Hultberg, B., Anderrson, A. & Lindgren, A. (1997)
Marginal folate deficiency as a posssible cause
of hyperhomocysteinaemia in stroke patients.
Eur. J. Biochem. Clin. Biochem., 35, 25-28.
Meicklejohn, D.J., Vickers, M.A., Dijkhuisen, R. &
Greaves, M. (2001) Plasma homocysteine concentrations in the acute and convalescent periods of atherothrombotic stroke. Stroke, 32,
57-62.
Robins, Wahlin, T.B., Wahlin, A., Winblad, B. &
Backman, L. (2001) The influence of serum vitamin B12 and folate status on cognitive functioning in very old age. Biol. Psychol., 56,
247-265.
Robinson, K., Arheart, K., Refsum, H., Brattstrom, L.,
Boers, G., Ueland, P., Rubba, P., Palma-Reis, R.,
Meleady, R., Daly, L., Witteman, J. & Graham,
I. (1998) Low circulating folate and vitamin B6
concentrations: risk factors for stroke, peripheral vascular disease, and coronary artery disease.
European COMAC Group. Circulation, 97,
437-443.
Sacco, R.L., Roberts, J.K. & Jacobs, B.S. (1998) Homocysteine as a risk factor for ischemic stroke:
an epidemiological story in evolution. Neuroepidemiology, 17, 167-173.
Saw, S.M. (1999) Homocysteine and atherosclerotic
disease: the epidemiologic evidence. Ann.
Acad. Med. Singapore, 28, 565-568.
Selhub, J. & D’Angelo, A. (1998) Relationship between homocysteine and thrombotic disease.
Am. J. Med. Sci., 316, 129-141.
Selhub, J., Jacques, P.F., Rosenberg, I.H., Rogers, G.,
B12 and Folic Acid Levels in Acute Cerebral Infarction
Bowman, B.A., Gunter, E.W., Wright, J.D. &
Johnson, C.L. (1999) Serum Total Homocysteine Concentrations in the Third National Health
and Nutrition Examination Survey (1991-1994):
Population Reference Ranges and Contribution
of Vitamin Status to High Serum Concentrations. Ann. Intern. Med., 131, 331-339.
Selhub, J., Jacques, P.F., Bostom, A.G., Wilson, P.W.F.
& Rosenberg, I.H. (2000) Relationship between plasma homocysteine and vitamin status
in the Framingham study population. Impact of
folic acid fortification. Public Health Rev., 28,
117-145.
Siri, P.W., Verhoef, P. & Kok, F.J. (1998) Vitamins B6,
B12, and folate: association with plasma total
homocysteine and risk of coronary atherosclerosis. J. Am. Coll. Nutr., 17, 435-441.
Toole, J.F., Malinow, M.R., Chambless, L.E., Spence,
J.D., Pettigrew, L.C., Howard, V.J., Sides, E.G.,
Wang, C.H. & Stampfer, M. (2004) Lowering
homocysteine in patients with ischemic stroke
to prevent recurrent stroke, myocardial infarction, and death: the Vitamin Intervention for
Stroke Prevention (VISP) randomized controlled trial. JAMA, 291, 565-575.
Tsai, J.C., Wang, H., Parella, M.A., Yoshizumi. M.,
161
Sibinga, N.E.S., Tan, L.C., Haber, E., Chang,
T.H.T., Schlegel, R. & Lee, M.E. (1996) Induction of cyclin A gene expression by homocyteine in vascular smooth muscle cells. J. Clin.
Invest., 146, 146-153.
Verhoef, P., Stampfer, M.J. & Buring, J.E. (1996) Homocystein metabolism and risk of myocardial
infarction: relation with vitamins B6, B12 and
folate. Am. J. Epidemiol., 143, 845-859.
Verhoef, P., Kok, F.J., Kruyssen, D.A., Schouten, E.G.,
Witteman, J.C., Grobbee, D.E., Ueland, P.M. &
Refsum, H. (1997) Plasma total homocysteine,
B vitamins, and risk of coronary atherosclerosis. Arterioscler. Thromb. Vasc. Biol., 17,
989-995.
Verhoef, P. (2000) Hyperhomocysteinemia and risk of
vascular disease in women. Semin. Thromb.
Hemost., 26, 325-334.
Vila, N., Deulofeu, R., Chamorro, A. & Piera, C. (1998)
Plasma homocysteine levels in patients with
ischemic cerebral infarction. Med. Clin. (Barc),
110, 605-608.
Yilmaz, N., Yilmaz, M., Pence, S., Ozaslan, J.,
Kocoglu, H. & Yilmaz, G. (2001) Determination of serum B12 vitamin and folic acid levels
in patient with stroke. Acta Medica, 44, 37-39.