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. Author manuscript; available in PMC: 2023 Apr 17.
Published in final edited form as: Biol Psychol. 2023 Feb 18;178:108525. doi: 10.1016/j.biopsycho.2023.108525

The Mediating Role of Vitamin D in the Association Between Personality and Memory: Evidence from Two Samples

Yannick Stephan 1,*, Angelina R Sutin 2, Martina Luchetti 2, Damaris Aschwanden 3,4, Antonio Terracciano 4
PMCID: PMC10106409  NIHMSID: NIHMS1875882  PMID: 36806675

Abstract

Five-Factor Model (FFM) personality traits are consistently related to cognition in old age. However, little is known about the biological mediators of this association. The present study examined whether levels of Vitamin D mediated the association between personality and memory. Participants were adults aged 50 to 96 years from the Health and Retirement Study (HRS, N= 5,229) and the English Longitudinal Study of Ageing (ELSA, N= 4,249). In HRS, personality and demographic factors were assessed in 2012/2014, Vitamin D was assessed in 2016, and memory was assessed in 2018. In ELSA, personality and demographic factors were obtained in 2010/2011, Vitamin D was measured in 2012/2013, and memory was assessed in 2014/2015. In both samples, higher extraversion and conscientiousness were related to higher levels of Vitamin D, whereas higher neuroticism was related to lower Vitamin D. In both samples, higher Vitamin D partly mediated the association between both higher extraversion and conscientiousness and better memory. The association between higher neuroticism and worse memory at follow-up was partially mediated by lower Vitamin D in the HRS and ELSA. Vitamin D did not mediate the association between higher openness and better memory. The present study extends the personality-cognition literature by providing new replicable evidence that Vitamin D is a biological mediator.

Keywords: Personality, Vitamin D, cognition, memory

1. Introduction

There is consistent evidence for the association between Five-Factor Model personality traits (FFM) (McCrae & John, 1992) and cognition across adulthood (Chapman et al, 2012; Luchetti et al., 2016; Sutin et al., 2019). Higher neuroticism (the tendency to experience negative emotions and distress) is related to worse cognitive function (Chapman et al., 2012; Luchetti et al., 2016; Graham et al., 2021), whereas higher conscientiousness (the tendency to be self-disciplined and organized) is associated with better cognition (Chapman et al., 2012; Luchetti et al., 2016). This pattern of association is evident across different cognitive domains, such memory, speed-attention-executive function, visuospatial ability, fluency and reasoning (Chapman et al., 2017; Luchetti et al., 2021; Sutin et al., 2019a, 2019b; Sutin et al., 2022), and cognition rated by knowledgable informants (Best et al., 2021; Sutin et al., 2019). There is also evidence that openness (the tendency to be curious and creative) is associated with higher overall cognition (Graham et al., 2021; Luchetti et al., 2016), higher memory performance (Luchetti et al., 2021) and higher verbal fluency (Sutin et al., 2019). Less consistent evidence has been found for the association between extraversion (the tendency to experience positive emotions and to be sociable) and agreeableness (the tendency to be altruistic and cooperative) and cognitive function (Luchetti et al., 2016; Sutin et al., 2019).

Past research on the potential pathways through which personality is related to cognition has mostly focused on the role of health behaviors and cognitively stimulating activities (Allen et al., 2019; Hogan et al., 2012; Sutin et al., 2020). For example, higher neuroticism has been found to relate to worse memory performance in part though sedentary behavior, whereas the association between higher conscientiousness and better memory was mediated by less sedentary behavior and more physical activity (Allen et al., 2019). In addition, higher openness and conscientiousness and lower neuroticism have been found to relate to higher cognition because of their association with greater engagement in cognitive activities (Hogan et al., 2012; Jackson et al., 2020; Mercuri & Holtzer, 2021; Sutin et al., 2020). Furthermore, higher informant-rated engagement in cognitive activities mediates the association between higher responsibility (a facet of conscientiousness) and better cognitive performance (Sutin et al., 2022). The association between personality and cognition, however, is likely to operate through multiple factors beyond behavior. Biological pathways have been proposed to explain why personality is related to cognitive function in old age (Sutin et al., 2020, 2022), but this hypothesis has yet to be tested.

The present study focused on Vitamin D in the association between personality and cognition. Vitamin D is a fat-soluble steroid hormone that plays a crucial role in health (Autier et al., 2014). There are two major forms of Vitamin D: Vitamin D2 (ergocalciferol), which is mainly derived from plant-based foods, and Vitamin D3 (cholecalciferol), which is derived from animal tissues. Animal studies as well as systemic reviews and meta-analyses of observational studies indicate that Vitamin D deficiency is related to worse cognitive function (Goodwill & Szoeke, 2017; Latimer et al., 2014; Van der Shaft et al., 2013), and a higher risk of dementia (Chai et al., 2019). However, the evidence from randomized trials is mixed on whether Vitamin D supplementation has an effect on cognitive function or cognitive decline (Beauchet et al., 2021; Goodwill & Szoeke, 2017, Kang et al., 2021; Yang et al., 2020). Higher vitamin D is thought to relate to better cognition because it promotes the release of neurotrophic factors, such as the nerve growth factor, brain-derived neurotrophic factor, glial cell line–derived neurotrophic factor, and neurotrophin 3 (Khairy & Attia, 2021), and because of its neuroprotective, anti-inflammatory and positive vascular effects (Annweiler, 2016; Sultan et al., 2020). Furthermore, Vitamin D may have cognitive benefits through its effect on Vitamin D receptors (VDR) present in neurons and glial cells in brain areas crucial for cognition (Annweiler, 2016; Sultan et al., 2020). Therefore, Vitamin D level could be a potential biological pathway through which personality may be related to cognition. Despite the finding that both personality and Vitamin D are related to cognitive functioning, little is known about the association between personality and Vitamin D. To the best of our knowledge, one study found that higher extraversion and openness are related to higher Vitamin D concentration (Ubbenhorst et al., 2011). However, this study was conducted in a relatively small sample (N= 206), and could have been limited in power. There are, however, reasons to expect also an association between both neuroticism and conscientiousness and Vitamin D level. In particular, these traits are related to dietary habits that are directly implicated in level of Vitamin D. For example, higher conscientiousness is associated with healthy eating, including fish consumption (Pfeiler & Egloff, 2020; Weston et al., 2020), which is a major source of Vitamin D (Lehmann et al., 2015). In contrast, higher neuroticism is related to unhealthy eating and lower fish consumption (Pfeiler & Egloff, 2020; Weston et al., 2020), which may lead to Vitamin D deficiency. Both conscientiousness and neuroticism are also associated with clinical and behavioral factors related to Vitamin D. Specifically, higher conscientiousness and lower neuroticism are related to lower BMI (Sutin et al., 2016), higher physical activity (Sutin et al., 2016), and a lower likelihood of smoking (Hakulinen et al., 2015), which lower risk of Vitamin D deficiency (Aspell et al., 2019; Pereira-Santos et al., 2015; Yang et al., 2021).

The present study examined Vitamin D as a potential biological pathway that links personality to cognition in two large longitudinal samples of older adults. Episodic memory was used as the cognitive measure in the two samples. Memory is a critical cognitive function in everyday life, and poor memory is related to risk of frailty (Gale et al., 2017), functional limitations (Zahodne et al., 2013), and mortality (Sabia et al., 2010). Declines in memory are also a core symptom of Alzheimer’s disease and related dementias (Josefsson et al., 2019). It was hypothesized that higher Vitamin D would mediate the association between higher conscientiousness and openness and better memory. In addition, it was expected that the association between higher neuroticism and lower memory would be mediated by lower Vitamin D.

2. Method

2.1. Participants

Participants were from the Health and Retirement Study (HRS) and the English Longitudinal Study of Ageing (ELSA). Both studies were conducted in accordance with the World Medical Association Declaration of Helsinki. The Health and Retirement Study (HRS) is a nationally representative longitudinal study of adults living in the United States aged 50 years and older and their spouses and approved by the Institutional Review Board (IRB) at the University of Michigan. Written informed consent was obtained from all participants. Personality assessment and demographic factors were obtained from a random half of the sample in 2012 and from the other half in 2014. The combined 2012/2014 waves was used as the baseline measure. Vitamin D was obtained from the HRS 2016 Venuous Blood Study (VBS), and memory was assessed in 2018. A total of 12,364 participants provided complete personality and demographic factors at baseline. Of this sample, 7530 participants also had memory data in 2018. The final sample was composed of 5229 individuals aged from 50 to 96 years (59% women, Mean= 66.69, SD= 9.24) who also had data on Vitamin D. Attrition analysis indicated that participants with complete data at follow-up were younger (d= 0.22), more likely to be hispanic, scored lower on neuroticism (d= .05), and higher on extraversion (d= 0.10), openness (d= 0.07), agreeableness (d= 0.08), conscientiousness (d= 0.06), than those with incomplete data. No differences were found for sex, education and race. HRS data are publicly available at: https://hrs.isr.umich.edu/data-products/access-to-public-data.

ELSA is a panel study of a representative cohort of men and women living in England aged 50 years and over. ELSA has been approved by the National Research Ethics Service. All participants provided written informed consent. Personality traits were first assessed in ELSA at Wave 5 in 2010/2011. Vitamin D was available at Wave 6 in 2012/2013. Memory was measured at Wave 7 in 2014/2015. This wave was included to have a similar interval between the baseline assessment and Vitamin D assessment and between the Vitamin D assessment and follow-up memory and to maximize comparability with HRS. A total of 8,117 participants had complete personality and demographic data at baseline. Of this sample, 6,427 participants had memory data at follow-up. The final analyzed sample was composed of 4249 participants aged from 50 to 89 years (54% women, Mean= 65.55, SD= 7.86). Attrition analysis indicated that participants with complete data at follow-up were more likely to be white, younger (d= 0.13), more educated (d= 0.18), and more emotionally stable (d=0.07), extraverted (d= 0.13), open (d=0.11), and conscientious (d=0.12) than individuals without data at follow-up. There were no differences in agreeableness or sex. ELSA data are publicly available from the UK Data Service (UKDS, https://www.ukdataservice.ac.uk/).

2.2. Measures

2.2.1. Personality.

The Midlife Development Inventory [MIDI] (Zimprich et al., 2012) was used to assess personality in the HRS and ELSA. Participants rated how well 26 adjectives that assessed the five traits described them on a scale from 1 (not at all) to 4 (a lot). Example adjectives are: nervous (neuroticism), active (extraversion), curious (openness), caring (agreeableness), and organized (conscientiousness). Cronbach alphas were .72 and .68 for neuroticism, .76 and .76 for extraversion, .79 and .78 for openness, .79 and .80 for agreeableness, and .66 and .67 for conscientiousness in the HRS and ELSA, respectively.

2.2.2. Memory.

In both HRS and ELSA, memory was assessed by immediate and delayed recall tasks. Participants were given a list of 10 common words and were asked to recall as many words as possible immediately and after a delay of approximately 5 minutes. In line with existing research in HRS and ELSA (Hulur et al., 2022; Maharani et al., 2020), the number of words recalled correctly across the immediate and delayed recall tasks were summed (range: 0–20 words). This total memory score is commonly used in standardized assessments designed to screen for dementia (see Crimmins et al., 2011; Walsh et al., 2022), and it has been found to predict a range of important outcomes, including disability, cardiovascular diseases, and mortality (Infurna & Andel, 2018).

2.2.3. Vitamin D.

In the HRS, Vitamin D was measured using blood collection as part of the 2016 VBS study (Crimmins et al., 2016). The assays were conducted using Liquid Chromatography coupled to tandem Mass Spectrometry (LC/MS/MS) at the University of Michigan Advanced Research and Diagnostic Laboratory (ARDL). Vitamin D was measured as both Vitamin D2 and Vitamin D3. The lower limit of detection was less than 0.14 ng/mL for Vitamin D2 and less than 0.82 ng/mL for Vitamin D3. The coefficient of variation (CV) was 10.96 for Vitamin D2 and 5.27 for Vitamin D3. The correlation between Vitamin D3 and Vitamin D2 was −.26 (p<.001). In ELSA, Vitamin D was measured without differentiation between Vitamin D2 and D3. Blood samples were analyzed at the Royal Victoria Infirmary (Newcastle upon Tyne, UK). Serum 25(OH)D levels were measured by the Diasorin Liaison 25-hydroxyvitamin D immunoassay. The assay for 25(OH)D has an analytical sensitivity (lower detection limit) of 7·5 nmol/l. CV ranged from 8.7 to 9.4%. A natural log transformation was performed on Vitamin D2 and Vitamin D3 in HRS and on Vitamin D in ELSA.

2.3.4. Covariates.

Age, education, sex (coded as 1 for female and 0 for male), and race were included as covariates in both samples. Race was coded as 1 for African American and 0 for other in the HRS and as 1 for White and 0 for other in ELSA. Ethnicity (coded as 1 for Hispanic and 0 for not Hispanic) and year of personality assessment (coded as 1 for 2012 and 0 for 2014) were also included in the HRS.

2.3. Data Analysis

In both the HRS and ELSA, the mediating role of Vitamin D in the association between personality and memory was tested using the PROCESS macro (Hayes, 2018) using 5,000 bootstrapped samples and 95% bias-corrected confidence intervals. Separate analyses were conducted for each personality trait. In the HRS, Vitamin D2 and Vitamin D3 were entered simultaneously; Vitamin D was the single mediator in ELSA. For each analysis, demographic factors were controlled. Furthermore, year of personality assessment was included as covariate in the HRS. Additional analysis controlled for baseline memory in both samples. Sensitivity analyses tested whether vitamin D moderated the relationship between personality and memory at follow-up, by testing an interaction between Vitamin D and each personality trait in ELSA and between Vitamin D3 and Vitamin D2 and each trait in the HRS.

3. Results

Descriptive statistics are in Table 1. Results of the mediation analysis are in Table 2. In both samples, higher conscientiousness was related to higher memory at follow-up, whereas higher neuroticism was associated with lower memory. Higher extraversion and higher openness were also related to higher memory in both samples. Effect sizes for the difference in memory performance between individuals with values one standard deviation (SD) above and below the mean were d=0.25 (HRS) and d=0.24 (ELSA) for neuroticism, d=0.16 (HRS) and d=0.06 (ELSA) for extraversion, d=0.31 (HRS) and d=0.18 (ELSA) for openness, and d=0.26 (HRS) and d=0.17 (ELSA) for conscientiouness.

Table 1.

Characteristics of the Samples

HRS a ELSA b
Variables M/% SD M/% SD
Age 66.69 9.24 65.55 7.86
Sex [%female] 59% - 54% -
Education 13.16 2.91 4.37 2.18
Ethnicity [% Hispanic] 12% - - -
Race 15%c - 98%d -
Vitamin D2 /[ng/mL] 1.90 6.19 − -
Vitamin D3 [ng/mL] 31.15 13.57 − -
Vitamin D [nmol/L] - - 49.62 23.17
Follow-up Memory 10.08 3.41 10.75 3.59
Neuroticism 1.98 0.61 2.08 0.59
Extraversion 3.20 0.57 3.18 0.54
Openness 2.94 0.55 2.91 0.53
Agreeableness 3.52 0.49 3.51 0.47
Conscientiousness 3.38 0.47 3.33 0.47
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Note.

a

N= 5,229;

b

N= 4,249;

c

% African American;

d

% White.See method section for differences in measures across the two samples

Table 2.

Indirect Effects of Personality on Memory Through Vitamin D2 and D3 in the HRS and Vitamin D in ELSA

Personality to Mediators Mediators to Cognition Indirect Effect Total Effect Direct Effect
B (SE) B(SE) Estimate (95%CI) B(SE) B(SE)
HRSa
Neuroticism −.493***(.07) −.483***(.07)
Vitamin D2 .042(.02) .096*(.04) .004 (−.0007; .0118)
Vitamin D3 −.035**(.01) .419***(.09) −.015(−.0273; −.0047)
Extraversion .358***(.07) .344***(.07)
Vitamin D2 −.026(.03) .093*(.04) −.002 (−.0099; .0025)
Vitamin D3 .038**(.01) .424***(.09) .016(.0052; .0304)
Openness .529***(.08) .519***(.08)
Vitamin D2 .034(.03) .086*(.04) .003 (−.0015; .0097)
Vitamin D3 .016(.01) .426***(.09) .007(−.0039; .0183)
Agreeableness .312***(.09) .312***(.09)
Vitamin D2 .018(.03) .092*(.04) .002(−.0044; .009)
Vitamin D3 −.005 (.01) .442***(.09) −.002(−.0149; .0105)
Conscientiousness .663***(.09) .635***(.09)
Vitamin D2 −.046(.03) .091*(.04) −.004(−.0133; .0015)
Vitamin D3 .081***(.01) .395***(.09) .032(.0148; .0531)
ELSAb
Neuroticism −.520***(.08) −.505***(.08)
Vitamin D −.042**(.01) .360***(.09) −.015(−.0297; −.0043)
Extraversion .230**(.09) .201*(.09)
Vitamin D .078***(.01) .370***(.09) .029(.0119; .0495)
Openness .462***(.09) .454***(.09)
Vitamin D .022(.02) .377***(.09) .008(−.0027; .0223)
Agreeableness −.10(.10) −.104(.10)
Vitamin D .011(.02) .388***(.09) .004(−.0088; .0192)
Conscientiousness .451***(.10) .418***(.10)
Vitamin D .093***(.02) .355***(.09) .033(.0136; .0580)
Open in a new tab

Note.

a

N=5,229;

b

N= 4,249;

*

p<.05,

**

p<.01,.

***

p<.001.

Higher conscientiousness and extraversion were related to higher Vitamin D3 in HRS and higher Vitamin D in ELSA, whereas higher neuroticism was related to lower D3 in HRS and lower Vitamin D in ELSA. The differences in Vitamin D3 and Vitamin D between individuals with neuroticism, extraversion and conscientiousness values one SD above and below the mean were, respectively, d= 0.09 and d= 0.14, d= 0.08 and d= 0.23, and d=0.19 and d= 0.23. There was no association between personality and Vitamin D2 in the HRS. Openness and agreeableness were unrelated to Vitamin D in both samples.

As hypothesized, Vitamin D3 and Vitamin D partially mediated the association between conscientiousness and neuroticism and follow-up memory in HRS and ELSA, controlling for demographic factors (Table 2). Unexpectedly, the relationship between extraversion and memory was also partially mediated by Vitamin D3 and Vitamin D in the HRS and ELSA. This result suggests that higher conscientiousness and higher extraversion were related to better memory in part through higher Vitamin D, whereas higher neuroticism was associated with worse memory in part through lower Vitamin D. In the HRS and ELSA, respectively, Vitamin D3 explained around 5% and Vitamin D explained around 7% of the association between conscientiousness and memory at follow-up. In addition, Vitamin D3 and Vitamin D explained around 3% of the association between neuroticism and memory in HRS and ELSA, respectively. Finally, the relationship between extraversion and memory was explained by around 4% by Vitamin D3 and by around 13% by Vitamin D in the HRS and ELSA, respectively. Vitamin D did not mediate the link between either openness or agreeableness and memory in either sample. The pattern of mediation was similar when baseline memory was included as an additional covariate in HRS and ELSA. Finally, there was no evidence for for an interaction between personality and either Vitamin D3 or Vitamin D2 in the HRS or an interaction between personality and Vitamin D in ELSA.

Discussion

The present study examined Vitamin D as a potential biological pathway of the association between personality and memory function in two longitudinal samples of older adults. We found that lower neuroticism and higher extraversion and conscientiousness were associated with higher levels of Vitamin D in the HRS and ELSA. In line with our hypotheses, higher Vitamin D partially mediated the relation between higher conscientiousness and better memory, whereas lower Vitamin D partially mediated the relation between higher neuroticism and lower memory at follow-up. In contrast, the association between openness and memory was not mediated by Vitamin D. Unexpectedly, Vitamin D also mediated part of the relationship between higher extraversion and better memory. These associations were replicated in two independent samples from two countries. In HRS, the associations were observed with Vitamin D3, but not Vitamin D2. Vitamin D2 is mostly found in plants food and fungi and is in the diet of most adults (Cashman et al., 2014), and, indeed D2 had a much smaller standard deviation than D3 in the HRS sample. Furthermore, systematic reviews and meta-analysis of intervention studies show a higher potency of Vitamin D3 to raise Vitamin D levels than Vitamin D2 (Tripkovic et al., 2012; Wilson et al., 2017). Therefore, this stronger link between Vitamin D3 and Vitamin D could explain the replicable association with personality traits found across the two samples. The present study extends existing knowledge by providing replicable and robust evidence of a biological pathway linking personality to cognition in old age.

A novel finding of this study was the replicable associations between personality and Vitamin D, which is consistent with the behavioral and clinical profiles of these traits. Higher conscientiousness, for example, is associated with healthy dietary habits, including fish consumption (Pfeiler & Eglof, 2020; Weston et al., 2020), lower BMI (Sutin & Terracciano, 2016), lower risk of smoking (Hakulinen et al., 2015), and a more physically active lifestyle (Sutin et al., 2016), which are in turn associated with higher Vitamin D (Aspell et al., 2019; Lehman et al., 2015; Pereira-Santos et al., 2015; Yang et al., 2021). Extraversion is related to healthy eating habits (Mõttus et al., 2012), frequent physical activity (Sutin et al., 2016) and a lower risk of depression (Hakulinen et al., 2015), which may lead to higher Vitamin D. The physically active lifestyle of conscientious and extraverted individuals may increase their likelihood of sun exposure, which is a major source of Vitamin D (Wu et al., 2022). In contrast, individuals with higher neuroticism have behavioral and clinical profiles implicated in vitamin D deficiency, characterized by the adoption of unhealthy dietary habits (Pfeiler & Egloff, 2020; Weston et al., 2020), physically inactive lifestyle (Sutin et al., 2016), higher likelihood of smoking (Hakulinen et al., 2015), and a higher risk of obesity (Sutin & Terracciano, 2016). Furthermore, the potential for sun exposure of individuals high on neuroticism may be reduced due to their higher physical inactivity and sedentary behaviors. Higher neuroticism is also related to higher likelihood of depressive symptoms (Hakulinen et al., 2015), which are associated with lower levels of Vitamin D (Milaneshi et al., 2014). Furthermore, higher Vitamin D polygenic scores have been found to relate to lower neuroticism (Avinun et al., 2020), which suggests that some genetic overlap may also explain part of the association between neuroticism and Vitamin D. Overall, the replicable associations found between personality and both Vitamin D and Vitamin D3 is consistent with evidence of a close relationship between Vitamin D and Vitamin D3 (Tripkovic et al., 2012; Wilson et al., 2017), and suggests that similar behavioral and clinical pathways may explain these associations. This study also supports existing observational studies that link higher Vitamin D to better cognitive functioning (Goodwill & Szoeke, 2017; Latimer et al., 2014; Van der Schaft et al., 2013). In addition to the associations between personality and Vitamin D, and between Vitamin D and memory, the data supported the hypothesis that Vitamin D partially mediated the associations between personality and memory. This finding adds a biological pathway to previous evidence on behavioral mechanisms, such as the involvement in cognitively engaging activities and health behaviors (Best et al., 2021; Sutin et al., 2020, 2022). Thus, current and past evidence are consistent with a conceptual model in which individual differences in personality traits modulate cognitive functioning through behavioral and biological mechanisms.

Openness was related to better memory in HRS and ELSA. Vitamin D, however, did not mediate this association. This finding contrasts with evidence for a relationship between openness and Vitamin D (Ubbenhorst et al., 2011), as well as with studies reporting an association between this trait and healthy eating behaviors related to Vitamin D, including fish consumption (Latimer et al., 2014). Past research has found the association between openness and cognition was explained by engagement in cognitive activities (Hogan et al., 2012; Jackson et al., 2020; Mercuri & Holtzer, 2021; Sutin et al., 2020, 2022). The present study suggests that this association was not mediated by Vitamin D. More research is needed to test whether other biological factors explain this association or whether involvement in a diversity of cognitively-stimulating activities is the main explanatory pathway for this trait.

The present study has theoretical implications. Models and research on personality and cognition have typically focused on behavioral factors, including health behaviors and cognitive activities (Allen et al., 2019; Hogan et al., 2012; Sutin et al., 2021). The present study indicates that biological factors are also likely to operate in this association. Furthermore, this study adds to existing models and research on the link between personality and health (Friedman & Kern, 2014; Wright et al., 2022) by identifying an association with a biomarker of health. The present study has implications for the understanding of the mechanisms linking personality to cognitive impairment and dementia. Vitamin D deficiency, for example, has been associated with higher risk of cognitive impairment and dementia (Chai et al., 2019), and higher neuroticism and lower conscientiousness are consistent risk factors for dementia (Aschwanden et al., 2021). Vitamin D deficiency is a potential biological pathway through which personality is related to higher risk of cognitive impairment and dementia. This study also has practical implications. Indeed, personality assessment may improve the individualization of interventions using Vitamin D supplementation. For example, intervention studies could test whether individuals with high neuroticism, low extraversion, and low conscientiousness benefit more from Vitamin D supplementation, and ultimately help cognitive functioning.

The present study has several strengths, including the test of the mediating role of Vitamin D between personality and memory, three waves of measurements spaced out in time, and the replication in two large cohorts of older adults from two countries. There are also limitations. The design of the present study limits the possibility of determining causality. In addition, Vitamin D explained a relatively small part (from 3–13%) of the relationship between personality and memory, which was expected given there are multiple pathways from personality to memory and thus any one factor is likely to only account for part of the association. Furthermore, Vitamin D was not available at baseline in either HRS or ELSA, so it was not possible to examine change in vitamin D over time. This study did not control for dietary patterns and nutritional variables that may confound the association (Ioannidis, 2018), such as the use of Vitamin D supplements. Furthermore, the samples included only middle-aged and older adults, many of who had low Vitamin D, particularly in the ELSA. Finally, the present study was based on US and UK samples. Further research should test whether this pattern of mediation replicates in other cultures, such as Asian cultures.

In sum, the present study found a replicable mediating role of Vitamin D in the relation between personality and memory. The association between higher conscientiousness and higher extarversion and better memory was mediated in part by higher Vitamin D; whereas lower Vitamin D partially mediated the associations between higher neuroticism and worse memory. Additional research is needed to identify other biological pathways of the association between personality and cognitive function, impairment, and risk of dementia.

Acknowledgments:

The HRS is funded by the National Institute on Aging (NIAU01AG009740) and conducted by the University of Michigan. Funding for the English Longitudinal Study of Ageing is provided by the National Institute of Aging (grants 2RO1AG7644-01A1 and 2RO1AG017644) and a consortium of UK government departments coordinated by the Office for National Statistics.

Funding:

This work was supported in part by the National Institute on Aging of the National Institutes of Health (Grant Nos. R01AG068093, R01AG053297). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Footnotes

Conflicts of Interest: None

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