Physio-cognitive decline syndrome among middle-aged diabetes patients: Handgrip strength significantly correlates with glycaemic control and cognitive score

Aims

To investigate the correlation between glycaemic control with component of Physio-Cognitive Decline Syndrome (PCDS) and among each component of PCDS itself.

Methods

A cross sectional study was conducted (January 2021-November 2022) at Dr. Cipto Mangunkusumo Hospital, Jakarta, Indonesia on consecutively recruited T2DM outpatients aged 40-59 years old. Data on the latest three months HbA1c, hand grip strength (HGS), usual gait speed (GS), and Indonesian Montreal Cognitive Assessment (MoCA-Ina) were evaluated. Pearson or Spearman's test was used to analyse the correlations.

Results

There were 133 subjects with median age 53 (40-59) years. The PCDS was found in 48.1 % subjects, of which 64.1 % with uncontrolled glycaemia. Significant correlations were found between HGS and HbA1c (r = -0.24, R2 = 0.06, p < 0.01) and MoCA-Ina score (r = 0.21, R2 = 0.04, p < 0.05).

Conclusion

The higher HbA1c and the lower MoCA-Ina score, the weaker handgrip strength was.

Study on insulin resistance and ischemic cerebrovascular disease: A bibliometric analysis via CiteSpace

Background

It is reported that insulin resistance widely exists in non-diabetic patients with a recent history of transient ischemic attack (TIA) or ischemic stroke. There is currently strong evidence to prove the bidirectional effect of glucose metabolism disorders and stroke events. Therefore, it is necessary to retrospectively tease out the current status, hotspots, and frontiers of insulin resistance and ischemic cerebrovascular disease through CiteSpace.

Materials and methods

We searched the Web of Science (WOS) for studies related to insulin resistance and ischemic cerebrovascular disease from 1999 to April 2022, then downloaded the data into CiteSpace to generate a knowledge visualization map.

Results

A total of 1,500 publications relevant to insulin resistance and ischemic cerebrovascular disease were retrieved. The USA had the most articles on this topic, followed by PEOPLES R CHINA and JAPAN. WALTER N KERNAN was the most prolific author, whose research mainly focused on insulin resistance intervention after stroke (IRIS) trial. The most common keywords were myocardial ischemia, metabolic syndrome, ischemic stroke, cerebral ischemia, association, oxidative stress, inflammation, and adipose tissue. Major ongoing research trends include three aspects: (1) the association between insulin resistance and ischemic cerebrovascular disease in non-diabetic patients, (2) the intrinsic pathological mechanism between insulin resistance and ischemic cerebrovascular disease, and (3) early intervention of insulin resistance to improve the prognosis of stroke.

Conclusion

The results of this bibliometric study provide the current status and trends of clinical research publications in the field of insulin resistance and ischemic cerebrovascular disease. Insulin resistance is strongly associated with the occurrence of ischemic stroke, early neurological deterioration in stroke patients, post-stroke depression, and cerebral small vessel disease. Early treatment of insulin resistance can be an effective way to prevent the onset of ischemic stroke and improve stroke prognosis. This study may help researchers to identify hot topics and explore new research directions.

Insulin Resistance and Cognitive Impairment: Evidence From Neuroimaging

Insulin is a peptide well known for its role in regulating glucose metabolism in peripheral tissues. Emerging evidence from human and animal studies indicate the multifactorial role of insulin in the brain, such as neuronal and glial metabolism, glucose regulation, and cognitive processes. Insulin resistance (IR), defined as reduced sensitivity to the action of insulin, has been consistently proposed as an important risk factor for developing neurodegeneration and cognitive impairment. Although the exact mechanism of IR-related cognitive impairment still awaits further elucidation, neuroimaging offers a versatile set of novel contrasts to reveal the subtle cerebral abnormalities in IR. These imaging contrasts, including but not limited to brain volume, white matter (WM) microstructure, neural function and brain metabolism, are expected to unravel the nature of the link between IR, cognitive decline, and brain abnormalities, and their changes over time. This review summarizes the current neuroimaging studies with multiparametric techniques, focusing on the cerebral abnormalities related to IR and therapeutic effects of IR-targeting treatments. According to the results, brain regions associated with IR pathophysiology include the medial temporal lobe, hippocampus, prefrontal lobe, cingulate cortex, precuneus, occipital lobe, and the WM tracts across the globe. Of these, alterations in the temporal lobe are highly reproducible across different imaging modalities. These structures have been known to be vulnerable to Alzheimer's disease (AD) pathology and are critical in cognitive processes such as memory and executive functioning. Comparing to asymptomatic subjects, results are more mixed in patients with metabolic disorders such as type 2 diabetes and obesity, which might be attributed to a multifactorial mechanism. Taken together, neuroimaging, especially MRI, is beneficial to reveal early abnormalities in cerebral structure and function in insulin-resistant brain, providing important evidence to unravel the underlying neuronal substrate that reflects the cognitive decline in IR. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 2.

Altered Structural and Functional MRI Connectivity in Type 2 Diabetes Mellitus Related Cognitive Impairment: A Review

Type 2 diabetes mellitus (T2DM) is associated with cognitive impairment in many domains. There are several pieces of evidence that changes in neuronal neuropathies and metabolism have been observed in T2DM. Structural and functional MRI shows that abnormal connections and synchronization occur in T2DM brain circuits and related networks. Neuroplasticity and energy metabolism appear to be principal effector systems, which may be related to amyloid beta (Aβ) deposition, although there is no unified explanation that includes the complex etiology of T2DM with cognitive impairment. Herein, we assume that cognitive impairment in diabetes may lead to abnormalities in neuroplasticity and energy metabolism in the brain, and those reflected to MRI structural connectivity and functional connectivity, respectively.

Insulin resistance in ischemic stroke: Mechanisms and therapeutic approaches

The pathological condition of insulin resistance prevents the neuroprotective effects of insulin. Numerous studies have demonstrated that insulin resistance, as an independent risk factor for ischemic stroke, accelerates the formation of thrombosis and promotes the development of atherosclerosis, both of which are major mechanisms of ischemic stroke. Additionally, insulin resistance negatively affects the prognosis of patients with ischemic stroke regardless of whether the patient has diabetes, but the mechanisms are not well studied. We explored the association between insulin resistance and the primary mechanisms of brain injury in ischemic stroke (inflammation, oxidative stress, and neuronal damage), looking for potential causes of poor prognosis in patients with ischemic stroke due to insulin resistance. Furthermore, we summarize insulin resistance therapeutic approaches to propose new therapeutic directions for clinically improving prognosis in patients with ischemic stroke.

Brain microstructural abnormalities in type 2 diabetes mellitus: A systematic review of diffusion tensor imaging studies

Type 2 diabetes mellitus (T2DM) is associated with deficits in the structure and function of the brain. Diffusion tensor imaging (DTI) is a highly sensitive method for characterizing cerebral tissue microstructure. Using PRISMA guidelines, we identified 29 studies which have demonstrated widespread brain microstructural impairment and topological network disorganization in patients with T2DM. Most consistently reported structures with microstructural abnormalities were frontal, temporal, and parietal lobes in the lobar cluster; corpus callosum, cingulum, uncinate fasciculus, corona radiata, and internal and external capsules in the white matter cluster; thalamus in the subcortical cluster; and cerebellum. Microstructural abnormalities were correlated with pathological derangements in the endocrine profile as well as deficits in cognitive performance in the domains of memory, information-processing speed, executive function, and attention. Altogether, the findings suggest that the detrimental effects of T2DM on cognitive functions might be due to microstructural disruptions in the central neural structures.

Correlation between Fibrinogen and White Matter Hyperintensities among Nondiabetic Individuals with Noncardiogenic Ischemic Stroke

OBJECTIVE

The aim of the present study is to confirm the correlation between fibrinogen and the severity of cerebral white matter hyperintensities (WMHs) among nondiabetic patients with noncardiogenic acute ischemic stroke.

PATIENTS AND METHODS

A cross-sectional study of 170 consecutive patients with noncardiogenic acute ischemic stroke who underwent magnetic resonance imaging and vascular imaging was conducted. WMHs were classified into periventricular hyperintensity (PVH) and deep and subcortical WMH (DSWMH) using Fazekas rating scale. After adjustment for fibrinogen and other vascular risk factors, we determined which factors were independent of WMHs.

RESULTS

After adjustment for the vascular risk factors, prior ischemic stroke (odds ratio [OR] 4.153, 95% confidence interval [CI] 1.077-16.020, P = .039), fibrinogen level (OR 2.114, 95% CI 1.034-4.322, P = .040), and glycosylated hemoglobin A1c (OR .633, 95% CI .423-.947, P = .026) were independently and positively associated with PVH (P < .05); prior ischemic stroke (OR 2.841, 95% CI 1.469-5.493, P = .002), lipoprotein(a) (OR 1.002, 95% CI 1.000-1.005, P = .047), and fibrinogen levels (OR 1.788, 95% CI 1.170-2.732, P = .007) were independently and positively associated with DSWMH (P < .05).

CONCLUSIONS

Our study demonstrated that prior ischemic stroke and higher fibrinogen are associated with WMHs, regardless of PVH and DSWMH, in nondiabetic patients with noncardiogenic acute ischemic stroke. In addition, lipoprotein(a) might be an independent predictor of DSWMH in patients with noncardiogenic acute ischemic stroke.

Insulin resistance in ischemic stroke

Insulin resistance often refers to a pathological condition in which cells fail to respond to the normal actions of insulin. Increasing literature has noted a critical role of insulin resistance in the pathogenesis of ischemic stroke. Insulin resistance plays an important role in the pathogenesis of ischemic stroke via enhancing advanced changes of atherosclerosis. A variety of literature indicates that insulin resistance enhances platelet adhesion, activation and aggregation which are conducive to the occurrence of ischemic stroke. Insulin resistance also induces hemodynamic disturbances and contributes to the onset of ischemic stroke. In addition, insulin resistance may augment the role of the modifiable risk factors in ischemic stroke and induce the occurrence of ischemic stroke. Preclinical and clinical studies have supported that improving insulin resistance may be an effective measure to prevent or delay ischemic stroke.

Association between Low-density lipoprotein cholesterol and occipital periventricular hyperintensities in a group of Chinese patients: an observational study

BACKGROUND

While occipital periventricular hyperintensities (OPVHs) are among the most common mild white matter hyperintensities, the clinical factors associated with OPVHs remain unclear. In this study, we investigated the role of clinical factors in development of pure OPVHs.

METHODS

This study included 97 patients with OPVHs and 73 healthy controls. Univariate analysis of clinical factors in OPVH patients and controls was followed by binomial logistic regression analysis to identify clinical factors significantly associated with OPVHs.

RESULT

Univariate analysis indicated that age, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and apolipoprotein-B (Apo-B) levels differed significantly between the OPVH patients and controls (p < 0.05). Age and gender were correlated with OPVH scores (p < 0.05), while LDL-C, triglycerides, Apo-B and TC were anti-correlated with OPVHs scores (p < 0.05). Multivariate analysis indicated that LDL-C is negatively correlated with OPVHs (p < 0.05), and age is positively correlated with OPVHs (p < 0.001).

CONCLUSION

In summary, LDL-C was negatively and age was positively associated with OPVHs among Chinese patients in a hospital.

Diabetes mellitus and white matter hyperintensity

White matter hyperintensity (WMH) is a brain lesion detected as a high-intensity area in magnetic resonance imaging T2 and fluid-attenuated inversion recovery images, and it has been suggested that WMH reflects damage to small vessels in periventricular and subcortical areas. Although WMH has been linked to the incidence of stroke, more recently it has been clarified that WMH is also associated with progression of cognitive decline and functional disability, which are components of so-called geriatric syndrome. In addition to hypertension, which is the classical risk factor for WMH, evidence has been accumulating to suggest that diabetes mellitus could also be associated with WMH progression, and some studies have shown that WMH severity is correlated with cognitive decline in patients with diabetes. The factors that accelerate WMH formation in elderly patients with diabetes remain poorly defined. It is considered that insulin resistance is an exacerbating factor, but the effects of hypertension, dyslipidemia or other vascular risk factors have yet be clarified, and further studies are required.

Regional Gray Matter Atrophy Coexistent with Occipital Periventricular White Matter Hyper Intensities

White matter hyperintensities (WMHs) and brain atrophy often coexist in the elderly. Additionally, WMH is often observed as occipital periventricular hyperintensities (OPVHs) with low-grade periventricular (PV) white matter (WM) lesions and is usually confined within an anatomical structure. However, the effects of OPVHs on gray matter (GM) atrophy remain largely unknown. In this study, we investigated GM atrophy in OPVHs patients and explored the relationship between such atrophy and clinical risk factors. T1-weighted and T2-weighted Magnetic resonance imaging (MRI) were acquired, and voxel-based morphometry (VBM) analysis was applied. The clinical (demographic and cardiovascular) risk factors of the OPVHs patients and healthy controls were then compared. Lastly, scatter plots and correlation analysis were applied to explore the relationship between the MRI results and clinical risk factors in the OPVHs patients. OPVHs patients had significantly reduced GM in the right supramarginal gyrus, right angular gyrus, right middle temporal gyrus, right anterior cingulum and left insula compared to healthy controls. Additionally, OPVHs patients had GM atrophy in the left precentral gyrus and left insula cortex, and such atrophy is associated with a reduction in low-density lipoprotein cholesterol (LDL-C) and apolipoprotein-B (Apo-B).

Age-associated white matter lesions: the MRC Cognitive Function and Ageing Study

Cerebral white matter lesions (WML) are common in the aging brain and are associated with dementia and depression. They are associated with vascular risk factors and small vessel disease, suggesting an ischemic origin, but recent pathology studies suggest a more complex pathogenesis. Studies using samples from the population-representative Medical Research Council Cognitive Function and Ageing Study neuropathology cohort used post-mortem magnetic resonance imaging to identify WML for further study. Expression of hypoxia-related molecules and other injury and protective cellular pathways in candidate immunohistochemical and gene expression microarray studies support a role for hypoxia/ischemia. However, these approaches also suggest that immune activation, blood-brain barrier dysfunction, altered cell metabolic pathways and glial cell injury contribute to pathogenesis. These abnormalities are not confined to WML, but are also found in apparently normal white matter in brains with lesions, suggesting a field effect of white matter abnormality within which lesions arise. WML are an active pathology with a complex pathogenesis that may potentially offer a number of primary and secondary intervention targets.

Apolipoprotein E-dependent load of white matter hyperintensities in Alzheimer's disease: a voxel-based lesion mapping study

Introduction

White matter (WM) magnetic resonance imaging (MRI) hyperintensities are common in Alzheimer’s disease (AD), but their pathophysiological relevance and relationship to genetic factors are unclear. In the present study, we investigated potential apolipoprotein E (APOE)-dependent effects on the extent and cognitive impact of WM hyperintensities in patients with AD.

Methods

WM hyperintensity volume on fluid-attenuated inversion recovery images of 201 patients with AD (128 carriers and 73 non-carriers of the APOE ε4 risk allele) was determined globally as well as regionally with voxel-based lesion mapping. Clinical, neuropsychological and MRI data were collected from prospective multicenter trials conducted by the German Dementia Competence Network.

Results

WM hyperintensity volume was significantly greater in non-carriers of the APOE ε4 allele. Lesion distribution was similar among ε4 carriers and non-carriers. Only ε4 non-carriers showed a correlation between lesion volume and cognitive performance.

Conclusion

The current findings indicate an increased prevalence of WM hyperintensities in non-carriers compared with carriers of the APOE ε4 allele among patients with AD. This is consistent with a possibly more pronounced contribution of heterogeneous vascular risk factors to WM damage and cognitive impairment in patients with AD without APOE ε4-mediated risk.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-015-0111-8) contains supplementary material, which is available to authorized users.

Impact of regional white matter lesions on cognitive function in subcortical vascular cognitive impairment

OBJECTIVES

Exact characterization and localization of white matter lesions (WMLs) as they relate and contribute to vascular cognitive impairment is highly debated. The purpose of this study was to investigate the impact of WML on cognitive function by using a new anatomy-based classification method.

METHODS

We detected WML accurately by using a three-dimensional fluid-attenuated inversion recovery (3D FLAIR) imaging technique and subsequently segmented WMLs by using an anatomy-based method. Participants included 56 consecutive patients diagnosed with subcortical vascular cognitive impairment (SubVCI). The volume of WMLs in different anatomic regions was measured. The volume of the hippocampus, the corpus callosum (CC), any lacunar infarcts, total gray matter (GM), and total brain volumes were also calculated.

RESULTS

Hippocampal (P  =  0.005) as well as temporal WML volumes (P  =  0.039) were both independently associated with mini-mental state examination (MMSE) score. Only the parietal WML volume (P  =  0.000) was independently associated with Montreal Cognitive Assessment (MoCA) score. Frontal WMLs were independently correlated with executive function. Occipital WMLs were independently associated with visuospatial and recall function. Language impairment was independently correlated with both parietal GM and parietal WML volume. Functions related to orientation were independently associated with parietal WML volume.

DISCUSSION

The volume of WMLs in the temporal region as well as in the hippocampus were both independently associated with MMSE score. For the MoCA score, however, only parietal WML volumes were independently correlated. White matter lesions within different anatomic regions were separately correlated with different subdomains of cognitive function.

The Persistent and Broadly Modulating Effect of Inhibitory rTMS in Nonfluent Aphasic Patients

Background. While prior preliminary studies have broadened our understanding of how repetitive transcranial magnetic stimulation (rTMS) improves language outcomes in stroke patients with nonfluent aphasia, the evidence base of the effectiveness of this method remains inadequate. Objective. In this study, we aimed to strengthen the evidence that this approach improves language performance and to identify characteristics of patients predisposed to benefit most from this treatment. Methods. Fifty-six stroke patients with nonfluent aphasia were randomly allocated to a real or a sham stimulation group: Group A (n = 33), who underwent 10 sessions of 1-Hz rTMS over the contralesional pars triangularis (PTr), and Group B (n = 23), who received sham 1-Hz stimulation. We performed the Picture Naming Test and the Concise Chinese Aphasia Test (CCAT) at the baseline, post-rTMS intervention, and at 3-month follow-up. Results. Group A showed significantly greater improvement than Group B in CCAT scoring ( P < .001), object-naming accuracy ( P = .01), and naming reaction time ( P = .004). The CCAT scoring and naming testing changes for Group A were persistent at 3 months following intervention ( P = .008). Patients who had a lower contralesional rest motor threshold (rMT) were predisposed to a favorable therapeutic outcome ( P = .006), independent of aphasia type, severity, and duration. Conclusions. The results of this study provide evidence that inhibitory rTMS, through downregulating the circuitry of the right pars triangularis (PTr), achieves a persistent and broadly modulating effect, irrespective of aphasia severity and subtype. Patients who show lower rMT in the right motor system would seem to benefit the most from inhibitory rTMS.

Increased body mass index makes an impact on brain white-matter integrity in adults with remitted first-episode mania

BACKGROUND

Obesity is increasingly prevalent in bipolar disorder (BD) but data about the impact of elevated body mass index (BMI) on brain white-matter integrity in BD are sparse. Based on extant literature largely from structural magnetic resonance imaging (MRI) studies, we hypothesize that increased BMI is associated with decreased fractional anisotropy (FA) in the frontal, temporal, parietal and occipital brain regions early in the course of BD.

METHOD

A total of 26 euthymic adults (12 normal weight and 14 overweight/obese) with remitted first-episode mania (FEM) and 28 controls (13 normal weight and 15 overweight/obese) matched for age, handedness and years of education underwent structural MRI and diffusion tensor imaging scans.

RESULTS

There are significant effects of diagnosis by BMI interactions observed especially in the right parietal lobe (adjusted F(1,48) = 5.02, p = 0.030), occipital lobe (adjusted F(1,48) = 10.30, p = 0.002) and temporal lobe (adjusted F(1,48) = 7.92, p = 0.007). Specifically, decreased FA is found in the right parietal (F(1,48) = 5.864, p = 0.023) and occipital lobes (F(1,48) = 4.397, p = 0.047) within overweight/obese patients compared with normal-weight patients with FEM. Compared with overweight/obese controls, decreased FA is observed in right parietal (F(1,48) = 6.708, p = 0.015), temporal (F(1,48) = 10.751, p = 0.003) and occipital (F(1,48) = 9.531, p = 0.005) regions in overweight/obese patients with FEM.

CONCLUSIONS

Our findings suggest that increased BMI affects temporo-parietal-occipital brain white-matter integrity in FEM. This highlights the need to further elucidate the relationship between obesity and other neural substrates (including subcortical changes) in BD which may clarify brain circuits subserving the association between obesity and clinical outcomes in BD.

Subgroup of ADNI normal controls characterized by atrophy and cognitive decline associated with vascular damage

Previous work examining Alzheimer's Disease Neuroimaging Initiative (ADNI) normal controls using cluster analysis identified a subgroup characterized by substantial brain atrophy and white matter hyperintensities (WMH). We hypothesized that these effects could be related to vascular damage. Fifty-three individuals in the suspected vascular cluster (Normal 2) were compared with 31 individuals from the cluster characterized as healthy/typical (Normal 1) on a variety of outcomes, including magnetic resonance imaging (MRI) and cerebrospinal fluid (CSF) biomarkers, vascular risk factors and outcomes, cognitive trajectory, and medications for vascular conditions. Normal 2 was significantly older but did not differ on ApoE4+ prevalence. Normal 2 differed significantly from Normal 1 on all MRI measures but not on Amyloid-Beta1-42 or total tau protein. Normal 2 had significantly higher body mass index (BMI), Hachinksi score, and creatinine levels, and took significantly more medications for vascular conditions. Normal 2 had marginally significantly higher triglycerides and blood glucose. Normal 2 had a worse cognitive trajectory on the Rey's Auditory Verbal Learning Test (RAVLT) 30-min delay test and the Functional Activity Questionnaire (FAQ). Cerebral atrophy associated with multiple vascular risks is common among cognitively normal individuals, forming a distinct subgroup with significantly increased cognitive decline. Further studies are needed to determine the clinical impact of these findings.

High energy diets-induced metabolic and prediabetic painful polyneuropathy in rats

To establish the role of the metabolic state in the pathogenesis of polyneuropathy, an age- and sex-matched, longitudinal study in rats fed high-fat and high-sucrose diets (HFSD) or high-fat, high-sucrose and high-salt diets (HFSSD) relative to controls was performed. Time courses of body weight, systolic blood pressure, fasting plasma glucose (FPG), insulin, free fatty acids (FFA), homeostasis model assessment-insulin resistance index (HOMA-IR), thermal and mechanical sensitivity and motor coordination were measured in parallel. Finally, large and small myelinated fibers (LMF, SMF) as well as unmyelinated fibers (UMF) in the sciatic nerves and ascending fibers in the spinal dorsal column were quantitatively assessed under electron microscopy. The results showed that early metabolic syndrome (hyperinsulinemia, dyslipidemia, and hypertension) and prediabetic conditions (impaired fasting glucose) could be induced by high energy diet, and these animals later developed painful polyneuropathy characterized by myelin breakdown and LMF loss in both peripheral and central nervous system. In contrast SMF and UMF in the sciatic nerves were changed little, in the same animals. Therefore the phenomenon that high energy diets induce bilateral mechanical, but not thermal, pain hypersensitivity is reflected by severe damage to LMF, but mild damage to SMF and UMF. Moreover, dietary sodium (high-salt) deteriorates the neuropathic pathological process induced by high energy diets, but paradoxically high salt consumption, may reduce, at least temporarily, chronic pain perception in these animals.

Obesity is associated with reduced white matter integrity in otherwise healthy adults

Existing work demonstrates that obesity is independently associated with cognitive dysfunction and macrostructural brain changes; however, little is known about the association between obesity and white matter (WM) integrity. We explore this relationship in a large cohort of otherwise healthy subjects. The present study classified 103 adult participants from the Brain Resource International Database between 21 and 86 years of age without history of neurological, medical, or psychiatric illness according to BMI (normal weight, overweight, obese) and subjected them to diffusion tensor imaging (DTI). Resulting fractional anisotropy (FA) indexes for the corpus callosum and fornix were examined in relation to BMI and age in a multiple regression framework. Results indicated that increasing BMI was independently associated with lower FA in the genu, splenium, and fornix, and a BMI × age interaction emerged for FA in the splenium and body of the corpus callosum. When categorized, obese persons demonstrated lower FA than normal and overweight persons for all WM indexes, but no FA differences emerged between overweight and normal persons. Results indicate both a direct association between obesity and reduced WM tract integrity and an interaction between obesity and aging processes on certain WM tracts in otherwise healthy adults. While such findings suggest a possible role for adiposity in WM dysfunction and associated cognitive deficits, prospective studies are needed to clarify the nature of these relationships and elucidate underlying mechanisms.