Vitamin E Intake Is Associated with Lower Brain Volume in Haptoglobin 1-1 Elderly with Type 2 Diabetes

Abstract

Backgrounds:

The efficacy of vitamin E in prevention of diabetes-related complications differs by Haptoglobin (Hp) genotype.

Objective:

To examine the role of Hp genotype in the relationship of vitamin E intake with brain volume in cognitively normal elderly patients with type 2 diabetes.

Methods:

Brain volumes for the superior, middle, and inferior frontal gyri and for the middle temporal gyrus were generated from structural T1 MRI in 181 study participants (Hp 1-1: n = 24, Hp 2-1: n = 77, Hp 2-2: n = 80). Daily vitamin E intake was assessed using the Food Frequency Questionnaire. Analyses of covariance, controlling for demographic and cardiovascular variables was used to evaluate whether the association of daily vitamin E intake with brain volume was modified by Hp genotype.

Results:

Average age was 70.8 (SD = 4.2) with 40% females, and mean Mini-Mental State Examination score of 28.17 (SD = 1.90). A significant interaction was found between vitamin E intake and Hp genotype in inferior frontal gyrus’ volume; p = 0.0108. For every 1 microgram increase in vitamin E intake, the volume of the inferior frontal gyrus decreased by 0.955% for Hp 1-1 (p = 0.0348), increased by 0.429% for Hp 2-1 (p = 0.0457), and by 0.077% for Hp 2-2 (p = 0.6318). There were no significant interactions between vitamin E intake and Hp genotype for the middle (p = 0.6011) and superior (p = 0.2025) frontal gyri or for the middle temporal gyrus (p = 0.503).

Conclusions:

The effect of dietary vitamin E on the brain may differ by Hp genotype. Studies examining the impact of vitamin E on brain-related outcomes should consider Hp genotype.

Keywords

Brain volume diabetes haptoglobin genotype vitamin E

INTRODUCTION

Type 2 diabetes (T2D) has consistently been associated with increased risk for cognitive decline, mild cognitive impairment, and dementia [1]—both Alzheimer’s disease (AD) and vascular dementia. T2D has been estimated to contribute to 6–10% of dementia cases. Some diabetes related complications can be prevented (e.g., acute myocardial infarction, death from hyperglycemic crisis, stroke, and amputations) [2], suggesting that prevention of dementia in the context of diabetes may be feasible. However, not all preventive interventions are effective and/or safe for all diabetic subjects [3], underscoring the need to identify subpopulations of patients with T2D who are optimal candidates for each intervention.

Oxidative stress resulting from increased metabolic stress, formation of advanced glycation end products and glucose auto-oxidation [4] has been suggested as a leading mechanism underlying diabetes related complications, including dementia [5] and brain atrophy [6, 7]. Due to its high oxygen consumption, high lipid content, and low levels of antioxidants, the brain is more vulnerable to oxidative stress compared to other tissues [8, 9]; accordingly, reducing diabetes-related oxidative stress could potentially be neuroprotective.

Based on its antioxidant properties, the efficacy of vitamin E in prevention of diabetes-related complication has been widely studied [10]. However, the results of clinical trials have been inconclusive, with several trials suggesting vitamin E treatment may not be uniformly beneficial in reducing T2D-related complications [11]. In the HOPE study, which enrolled patients at high risk for cardiovascular events based on presence of cardiovascular disease or diabetes, treatment with vitamin E was not superior over placebo in prevention of cardiovascular complication across the entire cohort [11]. Similarly, in the Women’s Health Study (WHS), vitamin E treatment was not associated with reduced risk for major cardiovascular events during a 10-year follow up [12]. Data do suggest, however, that the inefficacy observed in clinical trials may be attributable to differential effects of vitamin E in sub-populations of patients with T2D including differences in genotype [4]. One genotype that appears to play a role is the haptoglobin (Hp) gene, which controls levels and type of Hp, a hemoglobin (Hb) binding protein and an antioxidant agent [13]. In humans, there are two functional alleles of Hp: Hp 1 and Hp 2, yielding three genotypes that differ in chemical and clinical properties: Hp 1-1, Hp 2-1, and Hp 2-2. Individuals carrying the Hp 2-2 genotype are at increased risk for vascular complication of T2D in the periphery [14], while those carrying the Hp 1-1 genotype are at increased risk for white matter hyperintensities (WMH), lacunar infarcts, and worse cognitive performance [15]. An analysis of treatment effect in the HOPE study by Hp genotype, demonstrated a 40–50% reduction in rates of myocardial infarction and cardiovascular death, respectively, in individuals with T2D and the Hp2-2 genotype treated with vitamin E supplementation compared to placebo [16]. In the WHS, a 15% reduced risk for cardiovascular events was observed in women with T2D and Hp 2-2 genotype [17, 18]. In the ICARE study, 1,434 patients with diabetes and Hp 2-2 genotype aged ≥55, were randomized to receive vitamin E supplementation treatment versus placebo. At 18-months follow up, vitamin E treatment was associated with a significantly reduced risk for myocardial infarction, stroke, and cardiovascular death [19], pointing toward the critical need to examine the role of Hp genotype in the context of diabetes-related brain insults. The relevance of Hp genotype to health-related outcomes has been demonstrated in the context of diabetes, but not in non-diabetic populations [20].

In the current study, we sought to determine the relationship between vitamin E intake and brain atrophy in selected brain regions (based on a priori knowledge of brain regions impacted by diabetes) in participants of the Israel Diabetes and Cognitive Decline (IDCD) study. Given that the effects of vitamin E in prior clinical trials differed by Hp genotype, we tested the extent to which the effect of vitamin E was moderated by genotype. We hypothesized that vitamin E would mitigate T2D related atrophy among individuals with Hp 2-2 genotype.

METHODS

The IDCD is a collaboration of the Icahn School of Medicine at Mount Sinai, NY, the Sheba Medical Center, Israel, and the Maccabi Health Services (MHS), Israel. All three IRB committees approved the study.

The IDCD is a longitudinal investigation aimed to assess the relationship of long-term T2D-related characteristics and cognitive decline [21]. Participants of the study are elderly (≥65 years old) with T2D. The present analysis focused on baseline data. IDCD subjects were randomly selected from the approximately 11,000 individuals with T2D listed in the diabetes registry of MHS, the second largest HMO in Israel. The MHS diabetes registry is an integral part of the MHS Electronic Patient Record (EPR) system and was established in 1998 to facilitate disease management and to improve treatment and outcomes. Entry criteria to the registry are any of the following: 1) HbA1c>7.25%; 2) Glucose >200 mg/dl on two exams more than three months apart; 3) purchase of diabetic medication twice within three months supported by a HbA1c>6.5% or Glucose >125 mg/dl within half a year; 4) diagnosis of T2D (ICD9 code) by a general practitioner, internist, endocrinologist, ophthalmologist, or Type 2 diabetes advisor, supported by a HbA1c>6.5% or Glucose >125 mg/dl within half a year. These criteria have been validated by twenty physicians in MHS against their own practice records [22]. The Diabetes Registry has collected detailed information on laboratory, medication, and diagnoses since 1998.

Subjects are eligible for the IDCD study if they are: listed in the MHS diabetes registry, live in the central area of Israel, are diagnosed with T2D, are aged ≥65 years, cognitively normal at baseline (based on a multidisciplinary weekly consensus conference), do not suffer from major medical, psychiatric, or neurological conditions that affect cognitive performance, have ≥3 HbA1c measurements in the diabetes registry, speak Hebrew fluently, and have contact with an informant for at least 10 hours per week.

The subject recruitment process has been described in detail previously [21]. Briefly, the Diabetes Registry and the MHS EPR are thoroughly screened by the MHS team in order to identify potential subjects, excluding anyone with an ICD code for dementia/dementia subtypes, treatment with prescribed cholinesterase inhibitors, or with a major psychiatric or neurological condition (e.g., schizophrenia or Parkinson’s disease) that could affect cognitive performance. Since the goal of the IDCD was to identify T2D-related characteristics that contribute to incident cognitive decline, mild cognitive impairment (MCI), and dementia, only cognitively normal participants were eligible at baseline. A simple random sampling method was used for participants’ selection. The study team then verifies their fluency in Hebrew and availability of a family member or caregiver who is willing to be an informant for the study. Subjects who are willing to participate in the study are assessed at their residence or at the Sheba Medical Center memory clinic, in two phases. First, they are visited by a study physician who, after the subjects have signed the informed consent form, performs medical, neurological, and nutritional assessments (Food Frequency Questionnaire, FFQ) and draws blood for inflammatory markers (Il-6, CRP), Haptoglobin, and APOE genotypes. In the second phase (optimally 2 weeks after the physician’s visit), subjects are visited by a neuropsychologist who administers a cognitive battery (described below), and questionnaires to the subject and informant for cognitive and functional impairment and for depression and behavioral disturbances characteristic of dementia. All subjects’ cognitive data are reviewed by a multidisciplinary consensus conference team in order to define the subjects’ cognitive status (cognitively normal, MCI, or dementia and its subtypes). If the subject is cognitively normal at baseline, the IDCD has follow up interviews, which occur at 18-month intervals. If the subject converts to dementia, there is no additional follow up. Subjects, who are diagnosed as MCI at baseline, are not included in the study; however, subjects who convert from cognitive normal status to MCI during follow up, continue to be followed until conversion to dementia.

Cognitive assessment

A thorough neuropsychological battery, described in detail elsewhere [21] was administered to all participants and used to determine cognitive status.

Hp typing

The procedure for Hp genotyped has been described in detail elsewhere [23]. Briefly, blood samples were taken into an EDTA-containing vacutainer tube and centrifuged within 6 h from phlebotomy. Serum was stored at –70°C until Hp typing was performed on stored plasma samples by polyacrylamide gel electrophoresis as previously described [23].

Vitamin E intake

Daily vitamin E intake was assessed using a version of the FFQ that was specifically developed and validated for the elderly population in Israel [24 –26]. Portion sizes were based on the Ministry of Health standard portion size booklet for the Israeli population, and estimates were based on the Israeli MABAT survey of the Israeli population [27]. At the time the MABAT study was performed (1999-2001), supplements were rarely used by the Israeli population (<2%), therefore, data on vitamin E from supplements was not systematically collected from participants as part of the FFQ administration in the present study. However, in order to reflect to some extent the contribution of vitamin E from supplements, data on purchase of vitamin E or multivitamin that includes vitamin E from supplements was retrieved from the MHS Diabetes Registry database. We did not have access to the doses of vitamin E from supplements that were consumed.

Analyses of FFQ data were completed at the S. Daniel Abraham International Center for Health and Nutrition at Ben-Gurion University. The nutrients database is based on the USDA, and vitamin E was calculated with α-tocopherol as the main form as well as β, γ, and δ tocopherols. Foods that explained over 80% of the between person variability were included in the final 127 items FFQ. The major contributors to the variation between elderly people of vitamin E were vegetable oils (28%), fried potatoes (6.5%), cookies (6%), and sunflower seeds (5.5%). The FFQ contained a weighted mean of all relevant products consumed by the population providing vitamin E estimates that were specifically based on the Israeli elderly population survey [24].

MRI procedures

Randomly selected participants from the IDCD cohort underwent a magnetic resonance imaging (MRI) scan. MRI scans were performed at the Sheba Medical Center, with a 3 Tesla scanner (GE, Signa HDxt, v16VO2). High-resolution (1 mm³) images were acquired using a 3D inversion recovery prepared spoiled gradient-echo (FSPGR) T1-weighted sequence (TR/TE = 7.3/2.7 s, 20° flip angle, TI 450 ms). T2-weighted fluid-attenuated inversion recovery (FLAIR) sequence was also acquired (TR/TE 9500/123 ms, axial slices, slice-width/gap 3/0.4 mm, 22 cm FOV, 64×64 matrix, 90° flip-angle).

Volumetric analysis

The T1 weighted anatomical images for each subject were processed using the Voxel Based Morphometry (VBM [28]) toolbox, developed by Gaser (http://www.fil.ion.ucl.ac.uk/spm/ext/#VBMtools) and implemented in Statistical Parametric Mapping (SPM8) software. This procedure included automated iterative skull stripping, segmentation of the images into gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) probability images, and spatial normalization of the GM images to a customized GM template in standard MNI (Montreal Neurological Institute) space. The GM maps were smoothed using an 8 mm Gaussian kernel. GM probability maps were thresholded at 0.1 to minimize inclusion of CSF and WM in the GM maps. Total intracranial volume (TICV) was calculated using the segmented and thresholded images (TICV = GM + WM + CSF). Based on a priori knowledge of brain regions impacted by diabetes, the analysis focused on the frontal cortex, specifically, regions of interest (ROIs) that included the superior, middle and inferior frontal gyri and the middle temporal gyrus (MTG) identified by using the ‘Human Automated Anatomical Labelling (AAL) atlas’ within the Wake Forest University PickAtlas (http://www.rad.wfubmc.edu/fmri) and extracted using the MarsBaR ROI toolbox as implemented in SPM8. Based on a priori knowledge on the brain regions impacted by T2D [29, 30], the analysis focused only on the frontal cortex and MTG.

White matter hyperintensities segmentation

We examined WMH in the whole brain using Statistical Parametric Mapping version 8 software (http://www.fil.ion.ucl.ac.uk/spm) and the VBM8 Lesion Segmentation Toolbox (LST), following previously described methods [31] on the T1 and FLAIR images. The LST automated method for quantifying white matter damage is reliable and has been shown to have a high degree of agreement with manual delineation of WMH in fluid-attenuated inversion recovery images [31]. The default LST settings were used with the exception of κ (k), a value indicating the threshold for the initial lesion mask. Visual inspection of the probability maps across participants by using various k values, to maximize sensitivity while reducing false positive results, indicated that a k = 0.15 was the optimal value for our sample images. This procedure generated one binary lesion image per participant from which a total lesion volume (in milliliters) map was calculated.

Statistical analysis

Patient socio-demographic (age at baseline and sex), cognitive (Mini-Mental State Examination, MMSE), brain volume (total intracranial volume), health (years in the IDCD registry, body mass index (BMI), diastolic and systolic blood pressure, triglycerides, and creatinine), and nutritional (total daily caloric intake, daily vitamin E intake) characteristics are summarized using descriptive statistics with continuous variables reported as mean (SD) and nominal variables reported as N (%). Comparison of patient characteristics by Hp genotype status is performed with the two-sample t-test and Pearson’s Chi-square test for continuous and nominal variables, respectively.

Analysis of covariance (ANCOVA) was performed for each of the four brain ROIs, to evaluate whether the association of daily vitamin E intake with volume was modified by Hp genotype carrier status. Based on previously found relationships between Hp genotype and prevention of other diabetes-related complications, we maintained three separate Hp genotype carrier status groups in our analysis: 1-1, 1-2, and 2-2 [15]. Brain volumes were natural log transformed to render distributions normal. For each of the four brain regions, slope estimates (representing the percent difference in mean brain volume of a particular region of the brain per 1microgram increase in daily vitamin E intake) are presented for the fully adjusted ANCOVA models accounting for socio-demographic (age and sex), number of years in the diabetes registry (as a proxy for diabetes duration), total intra cranial volume, total caloric intake and BMI and for BMI² (due to the non-linear relationship with BMI), systolic and diastolic blood pressure, creatinine, triglycerides, cholesterol levels (total, LDL and HDL),WMH volume, and vitamin E intake from supplements. Tests of interaction are essentially testing equality of slope estimates for Hp 1-1, 1-2, and 2-2 carrier status groups. Given that multiple hypothesis tests are performed, to control the familywise error rate of 0.05, a Bonferroni correction was applied adjusting the threshold to determine statistical significance of interaction effects for each of our four brain volume endpoints to 0.05/4 = 0.0125, so in order for an interaction to be considered statistically significant, the calculated p-value had to be below 0.0125.

All statistical analyses were performed using SAS Version 9.4 (SAS Institute, Inc., Cary, NC) with hypothesis testing conducted at the 5% (2-sided) level of significance.

RESULTS

One hundred and eighty-one IDCD participants had full demographic, health-related, nutrition and brain imaging data and were included in the analysis: 24 Hp 1-1 carriers, 77 Hp 1-2 carriers, and 80 Hp 2-2 carriers. Average age was 70.8 (SD = 4.2), 40% of the sample were females, average number of years in the diabetes registry was 9.49 (SD = 4.49), and mean MMSE score was 28.17 (SD = 1.90), consistent with normal cognitive status. Hp genotypes did not differ in terms of demographic, cognitive, health-related, or brain volume variables. Similarly, groups did not differ in daily total caloric or vitamin E intake from food or from supplements (Table 1).

Table 1

Sample characteristics

Characteristic	Variable	HP 11 (N = 24)	HP 2-1 (N = 77)	HP 2-2 (N = 80)	Overall (N = 181)
Demographic	Age at Baseline (y)	70.71 (3.38)	71.19 (4.38)	70.49 (4.21)	70.82 (4.18)
	Female (%)	11 (46%)	32 (42%)	29 (36%)	72 (40%)
Cognitive	MMSE	28.08 (1.77)	28.16 (2.28)	28.22 (1.51)	28.17 (1.90)
Health	Years in Registry	9.90 (5.13)	9.35 (4.43)	9.49 (4.39)	9.49 (4.49)
	BMI (kg/m²)	28.48 (5.96)	27.98 (4.18)	28.98 (4.27)	28.49 (4.49)
	DBP (mmHg)	76.56 (5.13)	76.50 (4.73)	76.97 (5.30)	76.72 (5.02)
	SBP (mmHg)	131.77 (8.13)	133.08 (10.59)	133.86 (8.65)	133.25 (9.44)
	Triglyceride (mg/dl)	129.98 (50.32)	160.88 (106.21)	149.08 (50.79)	151.57 (79.50)
	Creatinine	0.94 (0.15)	0.98 (0.20)	1.00 (0.20)	0.98 (0.19)
	Total Cholesterol (mg/dl)	181.42 (22.31)	177.11 (26.36)	179.39 (25.67)	178.69 (25.47)
	LDL (mg/dl)	106.53 (19.31)	97.44 (20.74)	103.14 (19.26)	101.16 (20.09)
	HDL (mg/dl)	49.41 (11.29)	49.08 (11.52)	47.13 (10.44)	48.26 (11.01)
Brain Volume (ccs)	Total ICV	1,301.69 (119.79)	1,323.78 (127.25)	1,340.17 (148.25)	1,328.09 (135.95)
	Middle temporal gyrus	0.43 (0.04)	0.43 (0.03)	0.42 (0.04)	0.43 (0.04)
	Inferior frontal gyrus	0.33 (0.03)	0.33 (0.03)	0.33 (0.04)	0.33 (0.03)
	Middle frontal gyrus	0.32 (0.03)	0.33 (0.03)	0.32 (0.04)	0.32 (0.03)
	Superior frontal gyrus	0.30 (0.04)	0.31 (0.03)	0.30 (0.04)	0.30 (0.04)
	WMH	9.9 (9.2)	16.8 (25.5)	12.6 13.6)	14.0 (18.8)
Nutritional (daily intake)	Vitamin E (mg)	12.62 (4.49)	14.77 (5.59)	15.05 (7.08)	14.61 (6.19)
	Tocopherol α (mg)	9.61 (3.53)	11.07 (3.94)	11.37 (5.04)	11.01 (4.43)
	Tocopherol β (mg)	0.10 (0.05)	0.12 (0.07)	0.12 (0.10)	0.11 (0.08)
	Tocopherol γ (mg/d)	2.53 (1.10)	3.15 (1.75)	3.09 (2.00)	3.04 (1.80)
	Tocopherol δ (mg/d)	0.38 (0.26)	0.44 (0.28)	0.47 (0.33)	0.45 (0.30)
	Vitamin E from supplements^*	10 (42%)	28 (36%)	33 (41%)	71 (39%)
	Total Daily Caloric Intake (kcal)	1,931.09 (592.41)	2,014.83 (620.22)	2,145.14 (708.73)	2,061.32 (658.81)

^*Differences in variable characteristics between groups by Hp genes, i.e., p < 0.05, were not observed. MMSE, Mini-Mental State Examination; BMI, body mass index; DBP, diastolic blood pressure; SBP, systolic blood pressure; LDL, low density lipoprotein; HDL, high density lipoprotein; ICV, intracranial volume; ccs, cubic centimeters; WMH, white matter hyperintensities; Vitamin E from supplements, based on Maccabi health services (MHS) database on purchase of vitamin E or multivitamins.

ANCOVA revealed a significant interaction between vitamin E intake and Hp genotype in inferior frontal gyrus p = 0.011 (Table 2). In Hp 1-1 carriers, the volume of the inferior frontal gyrus decreased by 0.955% for every 1 microgram increase in vitamin E; p = 0.035 (Table 2). In contrast, among Hp 2-1 carriers, the volume of the inferior frontal gyrus increased by 0.429% for every 1 microgram increase in vitamin E; p = 0.046. In Hp 2-2 carriers, the volume of the inferior frontal gyrus increased by 0.077% for every 1 microgram increase in vitamin E; p = 0.632, though this association did not reach statistical significance.

Table 2

Exponential back transformed estimates from ANCOVA model for inferior frontal gyrus volume to evaluate the interaction between vitamin E intake and Hp genotype carrier status

Independent Variables	Dependent Variable: Inferior frontal Gyrus Volume
	Slope¹	95% CI	p ²
Interaction	p = 0.011^*
Vitamin E for Hp 1-1 Carriers	–0.955	[–1.833, –0.07]	0.035^*
Vitamin E for Hp 2-1 Carriers	0.429	[0.008, 0.852]	0.046^*
Vitamin E for Hp 2-2 Carriers	0.077	[–0.239, 0.393]	0.632
Covariates
Age	–0.792	[–1.157, –0.425]	<0.0001^*
Sex (male)	3.678	[–0.835, 8.397]	0.111
Years in Registry	–0.185	[–0.489, 0.12]	0.233
Total ICV (ml)	–0.003	[–0.016, 0.01]	0.607
Energy	0.001	[–0.001, 0.004]	0.290
BMI	–3.319	[–5.89, –0.678]	0.014^*
BMI²	0.047	[0.003, 0.091]	0.035^*
DBP	0.254	[–0.071, 0.58]	0.125
SBP	–0.088	[–0.242, 0.067]	0.264
Triglyceride	–0.023	[–0.064, 0.018]	0.270
Creatinine	–6.387	[–14.573, 2.583]	0.156
Cholesterol	0.254	[–0.053, 0.561]	0.105
LDL	–0.292	[–0.603, 0.021]	0.067
HDL	–0.121	[–0.421, 0.179]	0.427
WMH	–0.081	[–0.154, –0.009]	0.029^*
Vitamin E from supplements	1.548	[–1.29, 4.467]	0.286

¹Slope: Percent Change in dependent variable per 1-unit increase in independent variable; p²: Hypothesis Testing Slope = 0. Vitamin E ^* Hp genotype Interaction adjusted for all covariates listed in bottom section of Table 2. ^*p < 0.05. BMI, body mass index; DBP, diastolic blood pressure; SBP, systolic blood pressure; LDL, low density lipoprotein; HDL, high density lipoprotein; WMH, white matter hyperintensities.

There were no significant interactions between vitamin E intake and Hp genotype for the middle (p = 0.601) and superior (p = 0.2025) frontal gyri or for the MTG (p = 0.503) (Supplementary Tables 1–3).

Exponential back transformation to percent change in any specific brain region volume for a particular unit increase in vitamin E intake is based on the following formula, where N = number of vitamin E mcg: [exp(–0.009597*Nmcg)–1]*100% = % change in brain volume. For example, in Hp 1-1 carriers, for an increase of 6.2 mcg in vitamin E intake (6.2 mcg is the SD of vitamin E intake, see Table 1), the volume of the inferior frontal gyrus decreases by [exp(–0.009597*6.2)–1]*100 = 5.8%.

DISCUSSION

The present results demonstrated that in elderly subjects with T2D, Hp genotype moderated the association of vitamin E intake with inferior frontal gyrus volume such that in Hp 1-1 carriers, higher levels of vitamin E intake were significantly associated with lower volume of the inferior frontal gyrus. In Hp 2-1 and 2-2, the trend was in the opposite direction, approaching statistical significance for Hp 2-1. The association between vitamin E intake and Hp genotype on the volume of the middle and superior frontal gyri as well as for the MTG was not significant. This finding withstood adjustment for socio-demographic and clinical covariates as well as adjustment for multiple testing.

To the best of our knowledge, this is the first study to examine the role of Hp genotype on the association of vitamin E intake with brain volume. Our results suggest that dietary vitamin E may be associated with deleterious effects in patients with T2D carrying the Hp 1-1 genotype but not in non Hp 1-1 carriers, among whom it may have a beneficial effect.

The vulnerability of the inferior frontal gyrus may result from its location, peripheral to the primary distribution area of vascular systems, thus being a watershed area, which is more susceptible, compared to other brain regions, to the effects of cerebrovascular pathology. Vascular abnormalities, in turn, are more prevalent in patients with T2D carrying Hp 1-1 genotype [32] and may mediate the relationships of diabetes with brain atrophy [33]. The results of the present study, however, were not altered when WMH volume were included in the statistical model, possibly suggesting involvement of vascular pathologies other than WMH, not measured in the present study.

Vitamin E intake has been widely studied in the context of cognitive aging based on the recognized role of oxidative stress and free radicals in aging and neurodegeneration on the one hand [34], and the antioxidant properties of vitamin E on the other hand [35]. Elderly populations are at high risk of vitamin E deficiency [35 –37], which is associated with cognitive deficits as well as other age-related diseases (e.g., osteoporosis, sarcopenia, etc.) [35]. Vitamin E has been demonstrated to have a significant role in diabetes and its characteristics: lower intake of vitamin E [38] and vitamin E deficiency [39] were associated with higher levels of HbA1c in non-diabetic populations [38] and with higher risk for diabetes [39]. Moreover, people with diabetes may be at increased risk for vitamin E deficiency due to the prevalent use of cholesterol-lowering drugs, some of which may decrease vitamin E absorption [40]. In the present sample, blood levels of vitamin E were not measured, preventing the examination of the role of absorption on the relationship studied. However, it is important to note that vitamin E intake did not vary between groups. In both cases, intake was within the recommendations of the Food and Nutrition Board, Institute of Medicine, National Academies [41].

A beneficial effect of vitamin E in the prevention of cardiovascular complications in populations not necessarily suffering from T2D has not been demonstrated [4] with some studies even showing an association between high dose vitamin E supplementation and increased risk for all-cause mortality [42]. However, in T2D subjects carrying the Hp2-2 genotype, vitamin E supplementation was associated with a significant reduction in risk for cardiovascular events and mortality, thus changing the risk-benefit ratio. This benefit was not observed in other Hp genotypes [43]. In accordance with the present results, the effect of vitamin E supplementation on other T2D-related complications differed by Hp genotype; with 20–25% increased mortality and cardiovascular morbidity in Hp non- 2-2 carriers, and a 15% reduction in Hp 2-2 carriers [17]. A recent meta-analysis showed that vitamin E reduced CVD in patients with carrying the Hp 2-2 genotype but not in patients carrying Hp non 2-2 genotype [43]. These results suggest that despite the vulnerability of elderly with diabetes to vitamin E deficiency and its consequences, higher intakes of this vitamin should probably not be recommended indiscriminately to all patients.

The efficacy of vitamin E supplementation/intake on several brain related outcomes has been assessed in previous studies, none of which were limited to T2D subjects or stratified by Hp genotype. A nutritional pattern characterized by high intakes of polyunsaturated fatty acids (PUFA) and vitamin E was associated cross-sectionally with higher brain metabolic activity and higher gray matter volume in 52 non-diabetic cognitively normal individuals [44] and with higher white matter integrity in elderly participants of a multiethnic cohort [45]. In the Honolulu-Asia Aging study, midlife vitamin E intake did not modify the risk of late-life dementia or its most prevalent subtypes [46]. A recent Cochrane review demonstrated a possible effect of alpha tocopherol on slowing functional but not cognitive decline in AD, and no effect on prevention of dementia [47] or of conversion from MCI to dementia [48]. Inconsistent results were also shown in studies implementing cognitive performance rather than dementia status as an outcome. Some, but not all, studies [49] demonstrated that exposure to vitamin E alone or in combination with other supplements with anti-oxidative properties [50 –52] is associated with reduced risk for cognitive decline [50], better cognitive performance [51], lower prevalence and incidence of AD [50, 52], and of cognitive impairment without dementia [50]. Others have demonstrated that vitamin E supplementation is more effective in protecting against cognitive decline when vitamin E intake is low [53]. Discrepancies between studies may result from study population (age, gender, medical conditions, and cognitive status); follow up duration, source of vitamin E [54], duration of exposure to vitamin E, study outcome, etc. Interestingly, in contrast to supplement source of vitamin E, dietary intake was associated in clinical and epidemiological studies with better cognitive outcomes. In a neuropathological study, brain concentrations of γ-tocopherol, the most abundant form of vitamin E in the US diet, were associated with lower loads of amyloid and neurofibrillary tangles, the neuropathological hallmarks of AD. Brain levels of α-tocopherol, the most abundant form of vitamin E in supplements, were not associated independently with AD neuropathology. High α-tocopherol was associated with higher amyloid load when γ-tocopherol levels were low and with lower amyloid levels when γ-tocopherol levels were high [54]. The Hp protein has been demonstrated to affect amyloid-β uptake by glioblastoma-astrocytoma cells in vitro, thereby limiting the toxicity of this peptide [55]. It is yet unknown whether specific Hp genotypes differ in their capacity to affect amyloid-β accumulation and toxicity, but such differences are not biologically implausible. AD-related neuropathology may therefore be affected by the interaction of vitamin E intake and Hp genotype, stressing the importance of identifying T2D subjects that are optimal candidates for dietary/supplemental vitamin E intervention as a means for preventing the detrimental effects of T2D on the brain.

Strength of the present study are the well-validated diagnosis of T2D, access for numerous long-term T2D characteristics, and the use of the Hebrew version of the FFQ, which has been validated for the elderly Israeli population. However, a few limitations deserve note. The study focused on dietary vitamin E, and its consumption from supplements was not systematically collected as part of the FFQ questionnaire. We did, however, consider supplement vitamin E consumption (vitamin E, multivitamins) as reflected in medication purchase in the MHS database, in the multivariable linear regression models. The results remained unaltered. We did not have objective measurements of vitamin E levels in the blood. Furthermore, the present results are cross-sectional, but the longitudinal phase of the IDCD study is expected to deepen our understanding of the mechanisms involved in the detrimental effect of vitamin E intake on inferior frontal gyrus volume in T2D carrying the Hp 1-1 genotype. People who were not cognitively normal were excluded from entering the IDCD cohort at baseline; however, as the IDCD study longitudinal component progresses, we will be able to examine the inter-relationships of vitamin E, brain volume, and frank MCI and dementia. Additionally, replication using larger cohorts of Hp 1-1 carriers is needed. The present results cannot be compared to non-diabetic persons, in which the relevance of Hp genotype in cardiovascular outcomes has not been demonstrated. However, its interaction with vitamin E intake on brain-related outcomes in prediabetes states (such as obesity, insulin resistance), which, similarly to diabetes, increase the risk for brain pathology [56], should be examined in future studies.

Summary

In conclusion, the results of this study suggest that the effect of dietary vitamin E on the brain differ by Hp genotype. Randomized control trials that directly examine the impact of vitamin E treatment on brain-related outcomes may need to consider Hp genotype.

Footnotes

ACKNOWLEDGMENTS

This study was supported by the American Federation for Aging Research (AFAR), Young investigator award 2011 and NIRG-11-205083 Alzheimer’s Association, 2012 to RRS, the National Institute on Aging (grants R01 AG034087 to MS P50 AG05138 to Mary Sano), and the Helen Bader Foundation and the Leroy Schecter Foundation Award (to MS).

Authors’ disclosures available online ().

The supplementary material is available in the electronic version of this article: .

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