Serum Homocysteine,Vitamin B 12,Folate,and Their Association with Mild Cognitive Impairment and Subtypes of Dementia

Abstract

Background:

Although elevated levels of homocysteine (Hcy) are associated with cognitive impairment and dementia, the relevance of Hcy, vitamin B₁₂, and folate levels to subtypes of dementia are still unknown.

Objective:

To investigate the changes of Hcy, vitamin B₁₂, and folate levels in mild cognitive impairment (MCI) and subtypes of dementia including Alzheimer’s disease (AD), vascular dementia (VaD), frontotemporal dementia (FTD), and Lewy body dementia (LBD), and their relationships with cognitive function and magnetic resonance imaging (MRI) markers.

Methods:

We measured serum levels of Hcy, vitamin B₁₂, and folate in 257 subjects. Each subject underwent cognitive function assessment and brain MRI test. The Fazekas and temporal lobe atrophy (MTA) visual rating scales were used to assess the degree of white matter hyperintensities and MTA, respectively.

Results:

Serum levels of Hcy was higher and vitamin B₁₂ was lower in AD, VaD, FTD, and LBD groups than cognitively normal controls. No significant differences of folate levels were found among 6 groups. Hcy levels were positively correlated with MTA total score in AD (r = 0.448, p < 0.001). Vitamin B₁₂ levels were positively correlated with MoCA in VaD (r = 0.497), and negatively correlated with MTA total score in AD (r = – 0.325) (ps < 0.05). Hyperhomocysteinemia may increase the risk of AD (OR = 2.744), VaD (OR = 3.600), and FTD (OR = 3.244) in the adjusted model (ps < 0.05).

Conclusion:

Hcy and vitamin B₁₂ levels are associated with MTA in AD. Vitamin B₁₂ levels are associated with general cognition in VaD. Hyperhomocysteinemia is a risk factor for not only AD and VaD but also FTD.

Keywords

Alzheimer’s disease B vitamin dementia frontotemporal dementia homocysteine Lewy body dementia mild cognitive impairment vascular dementia

INTRODUCTION

Dementia is one of the largest contributors of disability across the world, leading to 10.4% neurological disability-adjusted life-years between 1990 and 2016 [1]. China has the largest number of patients with dementia in the world, which confers a heavy burden on society and patients’ families [2]. According to a recent epidemiological survey, there were about 15.07 million people (age ≥60) with dementia in China, of which 9.83 million with Alzheimer’s disease (AD), 3.92 million with vascular dementia (VaD), and 1.32 million with other dementias [3]. Besides, the number of patients with mild cognitive dementia (MCI) was about 38.77 millionin China.

Since there is still a limited efficient medicine for the treatment of dementia, it is of great significance for diagnosis, intervention, prevention, and treatment at the early stage of dementia [4, 5]. Among them, early modulations of modifiable risk factors for dementia are particularly critical. According to a review study, about one-third of dementia patients may be associated with seven modifiable risk factors including: low education, midlife hypertension, midlife obesity, diabetes, cognitive inactivity, smoking, and depression [6]. The risk of dementia can be effectively reduced by regulating dementia-related risk factors [7 –9].

Homocysteine (Hcy) is a non-essential sulfur amino acid, which is generated from methionine demethylation in vivo. It plays a core role in the methionine cycle and folate cycle and its metabolism depends on folate, vitamin B₁₂, B₆, and B₂. To date, a great number of studies have demonstrated that elevated Hcy and decreased B vitamins levels are modifiable risk factors for AD and VaD [10 –12]. And several clinical trials have shown that lowering Hcy level by B vitamin treatment may slow cognitive decline in elderly people [13, 14]. However, a meta-analysis reviewed 11 clinical trials and 22,000 individuals in all [15], which revealed that there was no significant effect on individual cognitive function by lower Hcy levels using B vitamin supplementation. Another recent systematic review published in 2022 [16] demonstrated lowering Hcy levels by B vitamin treatment may decrease the age-related cognitive decline in the East-Asia population. Despite inconsistent results in these studies, it is still necessary for scientists to explore the potential effect of Hcy and B vitamins ondementia.

Healthy population of plasma Hcy levels are between 5–15 μmol/l. Hyperhomocysteinemia is defined as higher Hcy levels above 15 μmol/l in plasma, and it is well recognized as a strong risk factor for cardiovascular and neurodegenerative diseases [17 –19]. Recently, Zhou et al. [20] conducted a dose-response meta-analysis of 29 prospective cohort studies and revealed that with every 5 μmol/L increase in blood Hcy levels, the relative risk of AD increased by 15%. In addition, previous studies reported that hyperhomocysteinemia is associated with an increased rate of hippocampal atrophy and cognitive decline in patients with AD [21, 22].

Although a large number of studies have demonstrated higher Hcy levels and lower B vitamin levels were risk factors for dementia, the differences of serum Hcy and B vitamin levels in different subtypes of dementia are still unclear. By cross-sectionally comparing subjects in MCI, AD, VaD, frontotemporal dementia (FTD), and Lewy body dementia (LBD) with cognitively normal controls (CN), we investigated the changes of serum Hcy, vitamin B₁₂, and folate levels, as well as their relationships with cognitive function, white matter hyperintensities (WMH) and medial temporal atrophy (MTA) in different groups.

MATERIALS AND METHODS

Subjects

According to the sample size calculation by PASS 15 (NCSS, Kaysville, UT, USA), at least 239 samples should be enrolled with the two-sided α of 0.05 and a power of 0.8. Finally, a series of 257 subjects were enrolled in this study from the memory clinic and department of neurology of Xuanwu Hospital in China between September 2020 to November 2021. All subjects gave written informed consent.

Subjects were considered as CN (n = 62) when scored 0 on the global Clinical Dementia Rating (CDR) scale. MCI (n = 36) was assigned when subjects were diagnosed with neither cognitively unimpaired nor dementia according to the modified Petersen’s criteria [23]. The diagnostic criteria for different forms of dementia were: 1) the NIA-AA criteria [24] for AD (n = 64); 2) the National Institute of Neurological Disorders and Stroke-Association Internationale pour la Recherche et l’Enseignement en Neurosciences (NINDS-AIREN) Work Group criteria [25] for VaD (n = 24); 3) the international behavioral variant FTD criteria consortium (FTDC) criteria [26] or Gorno-Tempini criteria [27] for FTD (n = 48); 4) the McKeith criteria [28] for LBD (n = 23). All diagnoses were performed by neurologists. The exclusion criteria were: 1) presence of severe heart, liver, kidney, thyroid dysfunction, and other systemic diseases that may cause cognitive impairment; 2) presence of metabolic encephalopathy, brain tumor, trauma, mental and neurodevelopmental retardation, and other neurological diseases that may cause brain dysfunction; 3) presence of ascertained infections, alcohol or drug abuse.

Laboratory tests

Blood samples were collected within 24 h for diagnostic purposes at the time of diagnosis. After coagulation at room temperature for 30 min, serum was collected by centrifuging at 3108× g for 5 min. Concentrations of serum Hcy, folate, and vitamin B₁₂ were measured by enzymatic cycling assay according to the kit instructions (Maccura Biotechnology Co., Ltd., Chengdu, China) with the Hitachi Automatic Analyzer 7600-210 (Hitachi, Tokyo, Japan).

Cognitive function and neuroimaging

The cognitive status for all subjects was conducted with Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), and CDR scale by the trained neurologist. All subjects underwent brain MRI scans including T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), DWI, and fluid-attenuated inversion recovery (FLAIR) by GE Discovery MR750 3.0T scanner. We used T2WI or FLAIR images to assess the grade of deep WMHs (DWM) and periventricular WMHs (PVH) according to Fazekas method (0 = absent, 1 = punctate foci, 2 = beginning confluence areas, 3 = large confluent areas). Total WMH score was defined as the summed scores PVH and DWM. And the MTA scores were used to identify the severity of right and left medial temporal atrophy ranging from 0 (no atrophy) to 4 (severe atrophy). The summed score of the left and right sides as the total MTA score was used for the purpose of analysis. All scoring was performed by the same neuroradiologist who was blinded to the diagnostic results.

Statistical analysis

Baseline demographic characteristics in different study groups were reported as mean ± SDs (continuous variables) or number with percentage (categorical variables). Comparisons among diagnostic groups were analyzed using one-way ANOVA for normal distribution variables, Kruskal-Wallis tests for skewness distribution variables, and chi-square test for categorical variables. Differences of serum Hcy, vitamin B₁₂, and folate between CN and other diagnostic groups were assessed by Mann-Whitney U test. A Bonferroni corrected p value (p < 0.05/5 = 0.01) was considered to be significant. Partial correlation analysis was used to examine the associations of serum Hcy, folate, and vitamin B₁₂ with cognitive function and MRI markers adjusting for age, sex, hypertension, diabetes, and dyslipidemia. Univariate logistic regression analysis was used to identify the crude odds ratio (ORs) for the prevalence of hyperhomocysteinemia (>15 μmol/L) in different diagnostic groups. Subsequently, the adjusted ORs controlling for age, sex, hypertension, diabetes, and dyslipidemia were carried out by multivariate logistic regression analysis. All statistical analyses were performed using SPSS statistics 26.0 (IBM, Armonk, NY, USA).

RESULTS

Baseline characteristics of subjects

Baseline characteristics of all 257 subjects separated into 6 different groups (CN = 62, MCI = 36, AD = 64, FTD = 48, VaD = 24, LBD = 23) are summarized in Table 1. There were significant age differences among 6 study groups. Subjects with LBD were significantly older than those with CN (p < 0.01). No significant differences in sex, hypertension, diabetes, and dyslipidemia were found among 6 study groups.

Table 1

Baseline characteristics of all subjects

Characteristics	CN	MCI	AD	VaD	FTD	LBD	p
Numbers(n)	62	36	64	24	48	23	–
Female (%)	28 (45.2%)	20 (55.6%)	34 (53.1%)	6 (25.0%)	28 (58.3%)	8 (34.8%)	0.064
Age (y)	61.40 ± 8.79	63.22 ± 7.27	65.08 ± 6.38	65.96 ± 7.22	62.10 ± 6.12	67.61 ± 7.74^a	0.002^**
Hypertension	34 (54.8)	21 (58.3)	44 (68.8)	18 (75.0)	28 (58.3)	14 (60.9)	0.442
Diabetes	9 (14.5)	8 (22.2)	7 (10.9)	8 (33.3)	7 (14.6)	3 (13.0)	0.168
Dyslipidemia	14 (22.6)	7 (19.4)	9 (14.1)	2 (8.3)	11 (22.9)	7 (30.4)	0.347

Data are shown as mean±SD. ^*p < 0.05, ^**p < 0.01, ^***p < 0.001. ^ap < 0.01, significantly different from control group after Bonferroni correction.

Serum homocysteine, vitamin B₁₂ and folate levels in all study groups

The serum levels of investigated Hcy, vitamin B₁₂, and folate in 6 different groups are shown as mean ± SDs in Table 2. Serum Hcy and vitamin B₁₂ levels were significantly different among 6 study groups (p < 0.05), while no significant difference of serum folate levels was reported (p = 0.330). After between group comparison, shown in Fig. 1, subjects in CN group demonstrated significant lower Hcy levels compared with AD, VaD, FTD, or LBD group (ps < 0.01). Serum levels of vitamin B₁₂ in CN group were significantly higher than AD, VaD, FTD, or LBD group (ps < 0.01). However, serum levels of Hcy and vitamin B₁₂ were not significantly different between CN group and MCI group (p > 0.05).

Table 2

Serum biomarkers, cognitive function, and

Characteristics	CN	MCI	AD	VaD	FTD	LBD	p
Homocysteine (μmol/L)	13.30 ± 6.29	13.86 ± 5.81	16.50 ± 5.83	17.85 ± 7.73	15.80 ± 6.07	16.60 ± 7.68	<0.001^***
Vitamin B₁₂ (pg/mL)	560.90 ± 3910.72	464.94 ± 3650.14	314.28 ± 2550.67	333.75 ± 2740.74	409.38 ± 3220.04	342.00 ± 2640.94	<0.001^***
Folate (ng/mL)	10.99 ± 6.82	9.25 ± 4.58	8.26 ± 4.74	9.44 ± 6.93	8.28 ± 5.26	9.04 ± 5.23	0.330
MMSE	28.10 ± 1.39	26.33 ± 2.11	15.53 ± 5.57	17.75 ± 6.46	15.58 ± 7.73	17.09 ± 8.90	<0.001^***
MoCA	25.40 ± 2.41	21.47 ± 2.82	10.95 ± 4.97	12.75 ± 5.95	10.40 ± 6.13	12.09 ± 7.45	<0.001^***
WMH total score	1.55 ± 1.34	2.28 ± 1.56	2.84 ± 1.84	4.54 ± 1.53	2.85 ± 2.02	2.91 ± 1.90	<0.001^***
PVH	0.87 ± 0.71	1.33 ± 0.76	1.50 ± 0.91	2.29 ± 0.75	1.54 ± 0.97	1.43 ± 0.95	<0.001^***
DWM	0.66 ± 0.72	0.94 ± 0.89	1.34 ± 1.01	2.25 ± 0.85	1.31 ± 1.15	1.48 ± 1.04	<0.001^***
MTA total score	0.73 ± 0.93	1.19 ± 1.24	4.14 ± 1.52	2.50 ± 2.09	2.92 ± 1.83	2.39 ± 2.10	<0.001^***
Left	0.35 ± 0.52	0.64 ± 0.68	2.09 ± 0.87	1.21 ± 1.14	1.54 ± 1.11	1.09 ± 1.12	<0.001^***
Right	0.37 ± 0.49	0.56 ± 0.65	2.05 ± 0.79	1.29 ± 1.00	1.38 ± 0.96	1.30 ± 1.11	<0.001^***

Data are shown as mean ± SD. ^*p < 0.05, ^**p < 0.01, ^***p < 0.001.

Fig. 1

Differences of serum levels of homocysteine, vitamin B₁₂, and folate in all subjects. ^*0.01 < p < 0.05, ^**0.001 < p < 0.01, ^***p < 0.001; After Bonferroni correction for multiple testes, p < 0.05/5 = 0.01 was considered significant.

Cognitive and imaging scores in all study groups

The results of MMSE, MoCA, visual rating WMH and MTA scores and bilateral comparisons are presented in Table 2 and Fig. 2, respectively. As expected, both MMSE and MoCA scores showed significant differences among 6 different groups (ps < 0.05), and all 4 different subtypes of dementia groups presented significant lower MMSE and MoCA scores compared to CN group (ps < 0.01), with the lowest MMSE score in AD group (15.53 ± 5.57) and the lowest MoCA score in FTD group (10.40 ± 6.13). There were significant differences of total WMH, PVH, DWM, total MTA, and both sides of MTA scores among 6 study groups (ps < 0.05). The total WMH, PVH, and DWH scores were significantly higher in subjects with AD, VaD, and FTD than CN (ps < 0.01). LBD group showed significant higher total WMH and DWH scores than CN group. Subjects with MCI and LBD showed trend-level increases of PVH scores compared with CN (0.01 < p < 0.05). But no significant difference of PVH score was found between CN and LBD group, and there were no significant differences of total WMH, PVH, and DWH scores between MCI and CN group. There were significant higher total MTA and both sides scores in subjects with 4 different subtypes of dementia compared with CN (ps < 0.01). And subjects with MCI reported no differences of total MTA or either side scores compared with CN.

Fig. 2

Differences of cognitive and imaging scores in all study groups. ^*0.01 < p < 0.05, ^**0.001 < p < 0.01, ^***p < 0.001; After Bonferroni correction for multiple testes, p < 0.05/5 = 0.01 was considered significant.

Relationships of serum homocysteine, vitamin B₁₂, and folate levels with cognitive function and MRI markers in different groups

The relationships among serum levels of Hcy, vitamin B₁₂, and folate in different groups are reported in Table 3. After age, sex, hypertension, diabetes, and dyslipidemia adjustments, serum Hcy levels were significantly inversely associated with serum vitamin B₁₂ levels in CN (r = –0.386, p = 0.003) and FTD (r = –0.371, p = 0.014) groups, and significantly inversely associated with serum folate levels in CN (r = –0.291, p = 0.028), FTD (r = –0.482, p = 0.001), and LBD (r = –0.605, p = 0.008) groups. Additionally, significant positive associations were found between serum vitamin B₁₂ and folate levels in CN (r = 0.295, p = 0.026), AD (r = 0.282, p = 0.031), and FTD (r = 0.355, p = 0.020) groups. However, there were no significant associations among serum Hcy, vitamin B₁₂, and folate levels in MCI and VaD groups.

Table 3

Partial correlation coefficients among serum homocysteine, vitamin B₁₂ and folate in different groups

	Hcy versus vitamin B₁₂	Hcy versus folate	vitamin B₁₂ versus folate
CN	–0.386 (0.003)	–0.291 (0.028)	0.295 (0.026)
MCI	0.113 (0.544)	0.133 (0.476)	0.146 (0.433)
AD	–0.250 (0.056)	–0.074 (0.577)	0.282 (0.031)
VaD	–0.341 (0.153)	–0.256 (0.291)	–0.073 (0.767)
FTD	–0.371 (0.014)	–0.482 (0.001)	0.355 (0.020)
LBD	–0.242 (0.334)	–0.605 (0.008)	0.084 (0.739)

The relevance of serum levels of Hcy, vitamin B₁₂, and folate to cognitive function and MRI markers in different groups are shown in Table 4. Subjects with MCI showed significant correlations between serum Hcy levels with MMSE (r = –0.513, p = 0.003), MoCA (r = –0.373, p = 0.039), and total WMH (r = 0.382, p = 0.034) scores. Besides, serum folate levels were significantly positively associated with total WMH score (r = 0.401, p = 0.026) in MCI group. In AD group, serum Hcy concentrations were significantly positively correlated with total MTA (r = 0.448, p < 0.001), left (r = 0.451, p < 0.001), and right (r = 0.378, p = 0.003) scores. Furthermore, serum levels of vitamin B₁₂ were significantly reversely correlated with total MTA (r = –0.325, p = 0.012) and right (r = –0.373, p = 0.004) scores in AD group, and significantly positively correlated with MoCA score (r = 0.497, p = 0.031) in VaD group. There were no significant relevance of serum Hcy, vitamin B₁₂ or folate levels with cognitive functional scales and MRI markers in CN, FTD, and LBD groups.

Table 4

Partial correlation coefficients of serum homocysteine, vitamin B₁₂, folate levels to cognitive function, WMH and MTA scores

	MMSE	MoCA	WMH total score	PVH	DWH	MTA total score	Left	Right
CN
Hcy	0.062 (0.644)	0.120 (0.375)	0.094 (0.486)	0.036 (0.788)	0.117 (0.387)	–0.013 (0.922)	0.009 (0.949)	–0.034 (0.803)
Vitamin B₁₂	–0.131 (0.333)	–0.187 (0.163)	–0.123 (0.361)	–0.037 (0.782)	–0.168 (0.211)	–0.001 (0.997)	0.012 (0.929)	–0.014 (0.920)
Folate	–0.016 (0.903)	–0.037 (0.787)	0.056 (0.678)	0.113 (0.402)	0.003 (0.981)	–0.111 (0.409)	–0.159 (0.239)	–0.044 (0.744)
MCI
Hcy	–0.513 (0.003)	–0.373 (0.039)	0.382 (0.034)	0.374 (0.038)	0.348 (0.055)	0.173 (0.353)	–0.017 (0.926)	0.341 (0.060)
Vitamin B₁₂	–0.134 (0.471)	–0.004 (0.983)	0.122 (0.514)	0.147 (0.431)	0.087 (0.642)	–0.081 (0.663)	–0.047 (0.800)	–0.104 (0.577)
Folate	0.035 (0.852)	0.117 (0.530)	0.401 (0.026)	0.379 (0.036)	0.376 (0.037)	–0.029 (0.875)	0.052 (0.782)	–0.109 (0.561)
AD
Hcy	–0.152 (0.251)	–0.176 (0.184)	0.116 (0.382)	0.107 (0.421)	0.115 (0.388)	0.448 (0.000)	0.451 (0.000)	0.378 (0.003)
Vitamin B₁₂	0.062 (0.639)	0.018 (0.893)	–0.229 (0.081)	–0.220 (0.094)	–0.218 (0.098)	–0.325 (0.012)	–0.236 (0.072)	–0.373 (0.004)
Folate	0.127 (0.338)	0.219 (0.096)	–0.063 (0.636)	–0.073 (0.581)	–0.049 (0.715)	–0.146 (0.270)	–0.130 (0.325)	–0.142 (0.285)
VaD
Hcy	–0.246 (0.310)	–0.225 (0.354)	–0.036 (0.884)	0.162 (0.507)	–0.209 (0.391)	0.324 (0.176)	0.317 (0.187)	0.313 (0.193)
Vitamin B₁₂	0.429 (0.067)	0.497 (0.031)	0.063 (0.798)	–0.034 (0.889)	0.143 (0.558)	–0.253 (0.295)	–0.256 (0.290)	–0.235 (0.332)
Folate	–0.283 (0.241)	–0.226 (0.352)	–0.255 (0.292)	–0.122 (0.619)	–0.349 (0.143)	–0.265 (0.272)	–0.202 (0.406)	–0.319 (0.184)
FTD
Hcy	0.016 (0.921)	–0.082 (0.600)	–0.133 (0.394)	–0.189 (0.225)	–0.068 (0.664)	0.169 (0.278)	0.269 (0.081)	0.001 (0.993)
Vitamin B₁₂	–0.177 (0.255)	–0.158 (0.311)	0.259 (0.094)	0.301 (0.050)	0.196 (0.208)	0.031 (0.846)	0.107 (0.493)	–0.073 (0.641)
Folate	0.001 (0.994)	–0.053 (0.734)	–0.063 (0.689)	–0.016 (0.921)	–0.103 (0.511)	0.011 (0.946)	–0.048 (0.760)	0.081 (0.605)
LBD
Hcy	–0.244 (0.329)	–0.267 (0.285)	0.063 (0.804)	–0.014 (0.956)	0.127 (0.615)	0.070 (0.782)	0.185 (0.463)	–0.064 (0.801)
Vitamin B₁₂	–0.331 (0.179)	–0.222 (0.377)	–0.412 (0.090)	–0.439 (0.068)	–0.337 (0.172)	0.042 (0.869)	0.120 (0.635)	–0.048 (0.848)
Folate	–0.111 (0.661)	–0.186 (0.460)	0.211 (0.401)	0.195 (0.439)	0.201 (0.425)	0.191 (0.449)	–0.008 (0.975)	0.381 (0.119)

^*p < 0.05, ^**p < 0.01, ^***p < 0.001.

Correlations of hyperhomocysteinemia with the risks of MCI and subtypes of dementia

Associations between hyperhomocysteinemia and the prevalence of MCI and subtypes of dementia are reported in Table 5. Subjects with AD (50.0%), VaD (62.5%), FTD (43.8%), and LBD (47.8%) showed higher proportions of hyperhomocysteinemia than CN (17.8%). Hyperhomocysteinemia showed positive associations with the risk of AD (OR = 4.636, p < 0.001), VaD (OR = 7.727, p < 0.001), FTD (OR = 3.606, p = 0.004), and LBD (OR = 4.250, p = 0.007) in the crude model. After adjustments of age, sex, hypertension, diabetes, and dyslipidemia, the relevance of hyperhomocysteinemia to the prevalence of AD (OR = 2.744, p = 0.034), VaD (OR = 3.600, p = 0.034), and FTD (OR = 3.244, p = 0.017) were still significant, while no longer significant to LBD. Moreover, there were no significant associations between hyperhomocysteinemia and the prevalence of MCI in either crude or adjusted model.

Table 5

Unadjusted and adjusted odds ratios (95% confidence intervals) for the prevalence of MCI and subtypes dementia according to hyperhomocysteinemia

	Crude model			Adjusted model
	n (%)	OR	(95% CI)	p	OR	(95% CI)	p
MCI	8 (22.2)	1.325	(0.477–3.676)	0.589	1.001	(0.328–3.053)	0.998
AD	32 (50.0)	4.636	(2.052–10.477)	<0.001^***	2.744	(1.080–6.974)	0.034^*
VaD	15 (62.5)	7.727	(2.698–22.134)	<0.001^***	3.600	(1.100–11.785)	0.034^*
FTD	21 (43.8)	3.606	(1.517–8.572)	0.004^**	3.244	(1.230–8.552)	0.017^*
LBD	11 (47.8)	4.250	(1.493–12.095)	0.007^**	2.630	(0.783–8.838)	0.118

^*p < 0.05, ^**p < 0.01, ^***p < 0.001.

DISCUSSION

The purpose of the present study was to investigate the differences of serum Hcy, vitamin B₁₂, and folate levels in MCI and different subtypes of dementia, and their relationships with cognitive function and MRI markers. This study revealed significant higher levels of serum Hcy and lower levels of vitamin B₁₂, while no difference of serum folate levels, in subjects with AD, VaD, FTD, and LBD compared with CN. Although numerous studies have compared Hcy, vitamin B₁₂, and folate concentrations in dementia patients with healthy controls, the results are still inconclusive. A study in Italy [29] reported that patients with AD and VaD showed increased levels of Hcy and decreased levels of folate compared with controls, while only AD patients showed an significantly reduced levels of vitamin B₁₂. In contrast, another study in South Korea [30] showed no differences of folate and vitamin B₁₂ levels between AD patients and controls. A Chinese population-based study [31] found patients with FTD had increased levels of Hcy and no differences of folate levels compared with control, which is consistent with our results. In addition, a recent study in Germany compared serum levels of Hcy, vitamin B₁₂, and folate among MCI, AD, VaD, FTD, LBD, and controls [32]. They found higher levels of Hcy in AD patients, lower levels of vitamin B₁₂ in AD and LBD patients, and lower levels of folate in AD patients compared with controls. Despite the results of these studies varies, most studies showed higher levels of Hcy in dementia patients than controls. And the possible reason for different results in studies may be ethnic differences, different prevalence of genetic variations such as methylene tetrahydrofolate reductase (MTHFR) and Transcobalamin II (TCN2), which may influence Hcy levels [33].

Since B vitamins play a role of cofactor in one-carbon metabolism, deficiency of vitamin B₁₂ and folate may lead to increased levels of Hcy [34, 35]. Consistent with this mechanism, our results showed inverse associations between Hcy and vitamin B₁₂ levels in CN and FTD groups, negative associations between Hcy and folate levels in CN, FTD, and LBD groups, and positive associations between vitamin B₁₂ and folate in CN, AD, and FTD groups. However, unlike our results, Quadri et al. [36]. revealed that Hcy levels were reversely correlated with vitamin B₁₂ and with folate in CDR 0.5 and AD groups. The possible reason is that the sample sizes are small in our study.

In the present study, we also investigated the relevance of serum levels of Hcy, vitamin B₁₂, and folate to cognitive function in subtypes of dementia. Our results found cognitive function test scores were only positively associated with Hcy levels in MCI patients, while negatively associated vitamin B₁₂ levels in MCI and VaD patients, after adjusting for age, sex, hypertension, diabetes, and dyslipidemia. Similarly, a Switzerland study [10] reported that the highest Hcy tertile had lower cognitive function test scores in MCI patients. However, inconsistent with our results, a cross-sectional survey in South Korea [30] suggested significant associations between plasma Hcy, vitamin B₁₂, folate, and cognitive function in both MCI and AD patients. Another study in Taiwan [37] revealed that higher levels of Hcy was associated cognitive decline in AD patients after following-up for 6 months.

Several studies have found elevated Hcy level is associated with cognitive decline [22], brain atrophy [7], neurofibrillary tangles [38], and white matter damage [39], which are all related to dementia. Hcy tends to affect cognitive function in a variety of pathways and often overlapping, including oxidative stress, DNA methylation, abnormal immune response, and protein aggregates precipitation [17]. Li et al. reported that elevated levels of Hcy can exacerbated amyloid-β pathology and tau pathology [40], both of which are AD-like pathology. Recent studies have shown that endothelial dysfunction may act as a new pathological mechanism causing WMH [41, 42]. Elevated Hcy levels may result in WMH by impairing endothelial function. Therefore, we further investigated the relationships between levels of Hcy, vitamin B₁₂, folate, and WMH in subtypes of dementia. Our results found that the associations between Hcy, folate levels, and WMH total scores were only significant in subjects with MCI. In 2005, Wright et al. reported that higher levels of total Hcy were associated with WMH after adjustment for sociodemographic and vascular risk factors [43]. A recent large population-based study in South Korea reported that elevated levels of Hcy was associated with PVH but not DWH [44]. However, there are few studies examined the relationships between Hcy, vitamin B₁₂, folate levels, and WMH in subtypes of dementia. Studies need to pay attention to the effect of Hcy on WMH in different types of dementia.

In addition, we found that serum Hcy levels were significantly positively associated with total MTA and both sides scores in AD patients, in contrast, significant negative relevance of vitamin B₁₂ to total MTA and right scores. An early study in 1998 reported that AD patients with higher Hcy levels at baseline had severer medial temporal atrophy than those with lower Hcy levels during a following-up for 3 years [21]. Similarly, a recent population-based autopsy study revealed that the highest Hcy quartile patients suffered more severe medial temporal atrophy [38], which was consistent with our results.

Hyperhomocysteinemia has been regarded as a strong modifiable risk factor for dementia, especially AD and VaD [45]. Nowadays, many studies have demonstrated several potential mechanisms to explain the connections between hyperhomocysteinemia and AD. An animal study in 2008 revealed that B vitamin deficient diet can induce hyperhomocysteinemia and impaired spatial learning and memory, and neurodegeneration [46]. Another animal study found that Herp, a homocysteine-responsive protein, can interacts with both PS1 and PS2, thereafter regulating PS-mediated amyloid-β generation [47]. In agreement with the findings of previous studies [30], there were significant higher proportions of hyperhomocysteinemic subjects in all subtypes of dementia compared with CN groups. And hyperhomocysteinemia may increase the risk of AD, VaD, and FTD, after adjusting for age, sex, hypertension, diabetes, and dyslipidemia. Hyperhomocysteinemia is a risk factor for both neurovascular diseases and neurodegenerative diseases. Studies have found that hyperhomocysteinemia is an independent risk factor for neurotoxicity and can lead to brain damage [48].

There are several strengths of our study. We compared the serum levels of Hcy, vitamin B₁₂, and folate in different subtypes of dementia, including AD, VaD, FTD, and LBD. And we further investigated the relevance of serum levels of Hcy, vitamin B₁₂, and folate to cognitive function and MRI markers in subtypes of dementia. However, a couple of limitations of our study need to be addressed. First, since single-center cross-sectional design, it is not adequate to interpret the correlation of serum Hcy, vitamin B₁₂, and folate levels with MMSE, WMH, or total MTA scores in different populations suffer from different subtypes of dementia. Second, visual rating scale may not be sensitive enough to detect the relevance of WMH with Hcy. Third, due to the relatively small sample size, we did not further classify VaD. Fourth, we did not control diet habits and nutritional status of subjects due to the lack of information.

In conclusion, we found that elevated serum Hcy levels is an independent risk factor for brain atrophy and hyperhomocysteinemia can increase the risk of AD, VaD, and FTD. Monitoring of serum Hcy levels in elderly population is of great importance for the prevention and treatment of dementia. More prospective cohort studies with larger sample sizes are needed to investigate the effects of serum Hcy, vitamin B₁₂, and folate levels on cognitive impairment in different stages and subtypes of dementia, especially those from multi-center and different races.

Footnotes

ACKNOWLEDGMENTS

This study was supported by the Key Project of the National Natural Science Foundation of China (U20A20354); Beijing Brain Initiative from Beijing Municipal Science & Technology Commission (Z201100005520016, Z201100005520017); the National Key Scientific Instrument and Equipment Development Project (31627803); the Key Project of the National Natural Science Foundation of China (81530036).

Authors’ disclosures available online ().

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Serum Homocysteine,Vitamin B 12,Folate,and Their Association with Mild Cognitive Impairment and Subtypes of Dementia

Abstract

Background:

Objective:

Methods:

Results:

Conclusion:

Keywords

INTRODUCTION

MATERIALS AND METHODS

Subjects

Laboratory tests

Cognitive function and neuroimaging

Statistical analysis

RESULTS

Baseline characteristics of subjects

Serum homocysteine, vitamin B12 and folate levels in all study groups

Cognitive and imaging scores in all study groups

Relationships of serum homocysteine, vitamin B12, and folate levels with cognitive function and MRI markers in different groups

Correlations of hyperhomocysteinemia with the risks of MCI and subtypes of dementia

DISCUSSION

Footnotes

ACKNOWLEDGMENTS

References

Serum homocysteine, vitamin B₁₂ and folate levels in all study groups

Relationships of serum homocysteine, vitamin B₁₂, and folate levels with cognitive function and MRI markers in different groups