Exploratory analysis of dietary intake and brain iron accumulation detected using magnetic resonance imaging in older individuals: the Lothian Birth Cohort 1936

Sex-Specific Associations of Dietary Iron Intake with Brain Iron Deposition on Imaging and Incident Dementia: A Prospective Cohort Study

OBJECTIVES

The study aimed to evaluate the association of dietary iron intake with incident dementia and brain iron deposition.

DESIGN/SETTING/PARTICIPANTS

We included dementia-free participants from the UK Biobank who completed at least one 24-hour dietary recall at study baseline (2009-2012) and were followed up to 2021. Incident dementia was determined through linkage to medical records and death registries. Brain MRI was conducted in a subgroup of participants since 2014, with T2* measurements being used as indicators of brain iron deposition.

MEASUREMENTS

Cox proportional hazard models were used to assess the associations of high (top quintile) and low (bottom quintile) versus medium (quintile 2 to 4) level of dietary iron intake with incident dementia, respectively. Linear regression was applied to assess the relations between dietary iron intake and brain T2* measurements.

RESULTS

During follow-up (mean = 9.5 years), a total of 1,454 participants (650 women and 804 men) developed dementia among 191,694 participants (55.0% female; mean age, 56.2 years). When adjusted for sociodemographic, lifestyle, and other dietary factors, participants with low dietary iron intake (< 10.05 mg/day) had a significantly higher dementia risk (hazard ratio [HR], 1.50, 95% confidence interval [CI], 1.19-1.89), while the relation for high intake (> 16.92 mg/day) was non-significant (HR, 1.16, 95% CI, 0.92-1.46). A significant gender difference (P-interaction < 0.001) was observed, with a U-shaped association in male participants (HR for low vs. medium, 1.56, 95% CI, 1.14-2.13; HR for high vs. medium, 1.39, 95% CI, 1.03 - 1.88; P-nonlinearity < 0.001) and no significant association in females, regardless of their menopause status. In general, dietary iron intake was not related to T2* measurements of iron deposition in most brain regions.

CONCLUSION

Our findings suggested a U-shape relationship between dietary iron intake and risk of dementia among males, but not females.

Perivascular spaces in the centrum semiovale at the beginning of the 8th decade of life: effect on cognition and associations with mineral deposition

Brain iron deposits (IDs) are indicative of microvessel dysfunction which may predispose to small vessel disease (SVD) brain damage and worsen cognition later in life. Visible perivascular spaces in the centrum semiovale (CSO-PVS) are SVD features linked with microvessel dysfunction. We examined possible associations of CSO-PVS volume and count with brain IDs and cognitive abilities in 700 community-dwelling individuals from the Lothian Birth Cohort 1936 who underwent detailed cognitive testing and multimodal brain MRI at mean age 72.7 years. Brain IDs were assessed automatically followed by manual editing. PVS were automatically assessed in the centrum semiovale and deep corona radiata supraventricular. General factors of overall cognitive function (g), processing speed (g-speed) and memory (g-memory) were used in the analyses. Median (IQR) volumes of IDs and CSO-PVS expressed as a percentage of intracranial volume were 0.0021 (0.011) and 0.22 (0.13)% respectively. Median count of CSO-PVS was 410 (IQR = 201). Total volumes of CSO-PVS and ID, adjusted for head size, were correlated (Spearman ρ = 0.13, p < 0.001). CSO-PVS volume, despite being correlated with all three cognitive measures, was only associated with g-memory (B = -114.5, SE = 48.35, p = 0.018) in general linear models, adjusting for age, sex, vascular risk factors, childhood intelligence and white matter hyperintensity volume. The interaction of CSO-PVS count with diabetes (B = -0.0019, SE = 0.00093, p = 0.041) and volume with age (B = 1.57, SE = 0.67, p = 0.019) were also associated with g-memory. Linear regression models did not replicate these associations. Therefore, it does not seem that CSO-PVS burden is directly associated with general cognitive ability in older age.

High iron intake is associated with poor cognition among Chinese old adults and varied by weight status-a 15-y longitudinal study in 4852 adults

Background

High body iron status has been shown to be associated with adverse health outcomes. However, the relation between high body iron status, body mass index (BMI), and cognition is still understudied.

Objective

This study aimed to examine the association between iron intake and cognitive function in Chinese adults and tested the interaction effect of iron intake and BMI on cognition.

Design

Longitudinal study data from a nationwide sample (n = 4852; age ≥55 y) from the China Health and Nutrition Survey during 1991-2006 were used. Of the participants, 3302 had completed cognitive screening tests in ≥2 surveys. Cognitive function was assessed in 1997, 2000, 2004, and 2006. Dietary iron intake was obtained from a 3-d food record during home visits in 1991, 1993, 1997, 2000, 2004, and 2006. Multivariable mixed linear regression and logistic regression were used.

Results

The cumulative mean ± SD iron intake in 1997 of tested subjects was 23.7 ± 11.3 mg/d (25.4 mg/d in men and 22.2 mg/d in women). High iron intake was associated with poor cognition. In fully adjusted models, across the quartiles of iron intake the regression coefficients (95% CIs) were 0, -0.39 (-0.77, -0.01), -0.55 (-0.95, -0.15), and -0.90 (-1.33, -0.47), respectively. Comparing extreme quartiles of iron intake (high), the OR (95% CI) for poor cognitive function was 1.30 (1.04, 1.64). There was a significant interaction between iron intake and BMI. The association between high iron intake and poor cognition was stronger among those with a high BMI than those with a low BMI. Among those with a BMI (kg/m2) >24, across quartiles of iron intake the ORs (95% CIs) for poor cognitive function were 1.00, 1.27 (0.91, 1.78), 1.41 (0.97, 2.04), and 2.04 (1.38, 3.01), respectively.

Conclusion

Higher iron intake is associated with poor cognition in Chinese adults, especially among those with a high BMI.

More evidence is needed. Iron, incident cognitive decline and dementia: a systematic review

Background

Our aim was to systematically review the relationship between iron and incident cognitive decline or dementia from midlife onwards.

Methods

Systematic review of eligible studies using Medline, Embase and PsycINFO^® for the period from 1 January 1986 to 2 December 2016 (CRD42016023800), where study populations had a mean age of over 50 years and were free of cognitive impairment or dementia at baseline. Two authors independently extracted data according to eligibility criteria and assessed study characteristics, quality and outcomes. Disagreement was resolved by discussion.

Results

A total of 1185 relevant records were identified with 12 full-text articles eligible for review. Six studies were excluded, leaving six texts to be included. Sample size ranged from 90 to 7173, with an average follow up of approximately 11.5 years. Baseline iron measures included brain iron (n = 2), iron-related biomarkers in blood and plasma (n = 2), and iron intake estimates from dietary records (n = 2). Outcomes were dementia incidence (n = 2) and longitudinal outcomes on neuropsychological tests (n = 4). Bias was evident across studies in one or more of the following: recruitment, iron exposure, outcome assessments, potential confounders, missing data or attrition.

Conclusions

Diversity across the small number of identified studies precludes conclusions regarding the role of iron in cognitive decline or dementia. Our review highlights substantial gaps in the evidence base and the need for more comprehensive, higher quality studies in this area.

Healthy cognitive ageing in the Lothian Birth Cohort studies: marginal gains not magic bullet

In the face of shifting demographics and an increase in human longevity, it is important to examine carefully what is known about cognitive ageing, and to identify and promote possibly malleable lifestyle and health-related factors that might mitigate age-associated cognitive decline. The Lothian Birth Cohorts of 1921 (LBC1921, n = 550) and 1936 (LBC1936, n = 1091) are longitudinal studies of cognitive and brain ageing based in Scotland. Childhood IQ data are available for these participants, who were recruited in later life and then followed up regularly. This overview summarises some of the main LBC findings to date, illustrating the possible genetic and environmental contributions to cognitive function (level and change) and brain imaging biomarkers in later life. Key associations include genetic variation, health and fitness, psychosocial and lifestyle factors, and aspects of the brain's structure. It addresses some key methodological issues such as confounding by early-life intelligence and social factors and emphasises areas requiring further investigation. Overall, the findings that have emerged from the LBC studies highlight that there are multiple correlates of cognitive ability level in later life, many of which have small effects, that there are as yet few reliable predictors of cognitive change, and that not all of the correlates have independent additive associations. The concept of marginal gains, whereby there might be a cumulative effect of small incremental improvements across a wide range of lifestyle and health-related factors, may offer a useful way to think about and promote a multivariate recipe for healthy cognitive and brain ageing.

Impact of high iron intake on cognition and neurodegeneration in humans and in animal models: a systematic review

Context

Accumulation of brain iron is linked to aging and protein-misfolding neurodegenerative diseases. High iron intake may influence important brain health outcomes in later life.

Objective

The aim of this systematic review was to examine evidence from animal and human studies of the effects of high iron intake or peripheral iron status on adult cognition, brain aging, and neurodegeneration.

Data Sources

MEDLINE, Scopus, CAB Abstracts, the Cochrane Central Register of Clinical Trials, and OpenGrey databases were searched.

Study Selection

Studies investigating the effect of elevated iron intake at all postnatal life stages in mammalian models and humans on measures of adult brain health were included.

Data Extraction

Data were extracted and evaluated by two authors independently, with discrepancies resolved by discussion. Neurodegenerative disease diagnosis and/or behavioral/cognitive, biochemical, and brain morphologic findings were used to study the effects of iron intake or peripheral iron status on brain health. Risk of bias was assessed for animal and human studies. PRISMA guidelines for reporting systematic reviews were followed.

Results

Thirty-four preclinical and 14 clinical studies were identified from database searches. Thirty-three preclinical studies provided evidence supporting an adverse effect of nutritionally relevant high iron intake in neonates on brain-health-related outcomes in adults. Human studies varied considerably in design, quality, and findings; none investigated the effects of high iron intake in neonates/infants.

Conclusions

Human studies are needed to verify whether dietary iron intake levels used in neonates/infants to prevent iron deficiency have effects on brain aging and neurodegenerative disease outcomes.

Dietary Iodine Exposure and Brain Structures and Cognition in Older People. Exploratory Analysis in the Lothian Birth Cohort 1936

BACKGROUND

Iodine deficiency is one of the three key micronutrient deficiencies highlighted as major public health issues by the World Health Organisation. Iodine deficiency is known to cause brain structural alterations likely to affect cognition. However, it is not known whether or how different (lifelong) levels of exposure to dietary iodine influences brain health and cognitive functions.

METHODS

From 1091 participants initially enrolled in The Lothian Birth Cohort Study 1936, we obtained whole diet data from 882. Three years later, from 866 participants (mean age 72 yrs, SD±0.8), we obtained cognitive information and ventricular, hippocampal and normal and abnormal tissue volumes from brain structural magnetic resonance imaging scans (n=700). We studied the brain structure and cognitive abilities of iodine-rich food avoiders/low consumers versus those with a high intake in iodine-rich foods (namely dairy and fish).

RESULTS

We identified individuals (n=189) with contrasting diets, i) belonging to the lowest quintiles for dairy and fish consumption, ii) milk avoiders, iii) belonging to the middle quintiles for dairy and fish consumption, and iv) belonging to the middle quintiles for dairy and fish consumption. Iodine intake was secured mostly though the diet (n=10 supplement users) and was sufficient for most (75.1%, median 193 µg/day). In individuals from these groups, brain lateral ventricular volume was positively associated with fat, energy and protein intake. The associations between iodine intake and brain ventricular volume and between consumption of fish products (including fish cakes and fish-containing pasties) and white matter hyperintensities (p=0.03) the latest being compounded by sodium, proteins and saturated fats, disappeared after type 1 error correction.

CONCLUSION

In this large Scottish older cohort, the proportion of individuals reporting extreme (low vs. high)/medium iodine consumption is small. In these individuals, low iodine-rich food intake was associated with increased brain volume shrinkage, raising an important hypothesis worth being explored for designing appropriate guidelines.

Do white matter hyperintensities mediate the association between brain iron deposition and cognitive abilities in older people?

BACKGROUND AND PURPOSE

Several studies have reported associations between brain iron deposits (IDs), white matter hyperintensities (WMHs) and cognitive ability in older individuals. Whether the association between brain IDs and cognitive abilities in older people is mediated by or independent of total brain tissue damage represented by WMHs visible on structural magnetic resonance imaging (MRI) was examined.

METHODS

Data from 676 community-dwelling individuals from the Lothian Birth Cohort 1936, with Mini-Mental State Examination scores >24, who underwent detailed cognitive testing and multimodal brain MRI at mean age 72.7 years were analysed. Brain IDs were assessed automatically following manual editing. WMHs were assessed semi-automatically. Brain microbleeds were visually counted. Structural equation modelling was used to test for mediation.

RESULTS

Overall, 72.8% of the sample had IDs with a median total volume of 0.040 ml (i.e. 0.004% of the total brain volume). The total volume of IDs, significantly and negatively associated with general cognitive function (standardized β = -0.17, P < 0.01), was significantly and positively associated with WMH volume (std β = 0.13, P = 0.03). WMH volume had a significant negative association with general cognitive function, independent of IDs (std β = -0.13, P < 0.01). The association between cognition and IDs in the brain stem (and minimally the total brain iron load) was partially and significantly mediated by WMH volume (P = 0.03).

CONCLUSIONS

The negative association between brain IDs and cognitive ability in the elderly is partially mediated by WMHs, with this mediation mainly arising from the iron deposition load in the brain stem. IDs might be an indicator of small vessel disease that predisposes to white matter damage, affecting the neuronal networks underlying higher cognitive functioning.