Deficiency and low status of the B-vitamins such as folate and vitamin B12 are highly prevalent in older populations. Estimates of vitamin B12 (B12) deficiency in those aged ≥ 50 years range from 5 to 40 % depending on the marker of measurement and the deficiency cut-off selected(Reference Andrès, Loukili and Noel1). The consequences of low B12 status can include megaloblastic anaemia, irreversible demyelinating neurological disease/paresthesia and the potential for impaired cognitive function(Reference Stabler2). Folate status is highly dependent on whether the country of residence has a mandatory folic acid (FA) food fortification policy. For instance, in the USA, mandatory food fortification with FA has resulted in folate deficiency/low status rates of just 1·2%(Reference Pfeiffer, Sternberg and Hamner3) in those aged ≥ 60 years. This is in direct contrast to countries such as the UK which have no such policy (deficiency rates range from 5 to 31 %)(Reference Bates, Prentice and Bates4). Recent data from the older Irish population have shown that one in seven people aged > 50 years has low folate status(Reference Laird, O’Halloran and Carey5). Similarly, one in eight older adults is reported to have low B12 status(Reference Laird, O’Halloran and Carey5), while low dietary intakes and low blood status have been reported throughout all age groups in the Irish population(Reference Hopkins, Gibney and Nugent6). This is not surprising given that Ireland, like the UK, has no policy of fortification with FA but allows voluntary food fortification. The foods that are most commonly fortified with FA are breakfast cereals(Reference Hennessy, Walton and Flynn7), while there is varying but inconsistent FA enrichment of other food items(Reference Kelly, Gibney and Boilson8). In terms of B12, foods that are fortified or rich in this micronutrient are not always regularly consumed by the older population and recent data have shown that dairy foods (which are rich in B-vitamins and B12) are only consumed in the recommended amounts by 4 % of older Irish adults(Reference Laird, Casey and Ward9).
These high deficiency rates and poor access to micronutrient-rich foods are of concern given the reported linkage of folate and B12 with depression. Low folate and B12 concentrations have been correlated with depressive disorders(Reference Wesson, Levitt and Joffe10–Reference Bell, Edman and Morrow15), while evidence has suggested that both of these vitamins may enhance the effectiveness of antidepressants(Reference Almeida, Ford and Hirani16). More recently, a large Irish cohort study of older Irish adults (n 5186) reported that the lowest quintile of erythrocyte folate compared with the highest was associated with an increased risk of depression(Reference Moore, Hughes and Hoey17). These associations are plausible given these B-vitamins are required for the synthesis of methionine which subsequently forms S-adenosylmethionine(Reference Bailey, Stover and McNulty18), which is the main methyl donor for the formation of monoamine neurotransmitters, phospholipids and nucleotides(Reference Bottiglieri and Reynolds19). However, the majority of studies examining the associations of these B-vitamins with depression are cross-sectional and have not controlled for important covariates, such as disease status, medication use or vitamin D status, which has been shown to an important predictor of depression(Reference Briggs, McCarroll and O’Halloran20). Understanding the link between folate/B12 status and depression in later life is important as depression is a risk factor for functional decline(Reference Sivertsen, Bjørkløf and Engedal21), admission to residential care(Reference Lenze, Schulz and Martire22) and early mortality(Reference Onder, Liperoti and Soldato23). Thus, the identification of risk or protective factors for this condition is of the upmost importance. Moreover, there is a growing momentum for the introduction of mandatory food fortification of these B-vitamins in Europe and the UK, and there is a need to understand links between these micronutrients with chronic conditions and health before fortification can be implemented.
Thus, the aim of this study is to examine the longitudinal relationship between baseline folate and B12 status and incident depressive symptoms up to 4 years later in a representative sample of the community-living population of Ireland aged 50 years and over.
Methods
Study design and participants
This study utilises data from the Irish Longitudinal Study on Ageing (TILDA), a nationally population-based representative sample of community-dwelling older Irish adults aged ≥ 50 years. As described in detail elsewhere(Reference Whelan and Savva24), the first wave of data collection (wave 1, 2009–2011) was conducted using a stratified clustered procedure to randomly sample postal addresses from the Irish Geo-Directory (a listing of all residential addresses in the Republic of Ireland). Wave 2 was conducted between 2011 and 2012 and wave 3 between 2014 and 2015. This sub-study within TILDA investigates the association of folate and vitamin B12 (wave 1) with incident depression at later recruitment waves. Therefore, participants were included in this study if they were aged ≥ 50 years and underwent assessment at wave 1 including measurement of plasma folate and plasma total B12 and screening for depression. Participants were excluded if they were missing blood data or had depression at wave 1 or did not complete 4-year follow-up, including assessment of incident depression at both wave 2 and wave 3.
Ethics
The study was approved by the Faculty of Health Sciences Research Ethics Committee at Trinity College Dublin, and all participants gave informed written consent. All experimental procedures adhered to the Declaration of Helsinki, and all assessments were performed by trained research nurses. Anonymised data and materials have been made publicly available at the Irish Social Science Data Archive based in University College Dublin and the Interuniversity Consortium for Political and Social Research based in the University of Michigan and can be accessed at http://www.tilda.ie.
Folate and vitamin B12 analysis
A non-fasting blood sample was collected by venepuncture into one 10 ml EDTA tube (BD, Becton, Dickinson Limited) by a trained phlebotomist. Samples were kept chilled during transport, were centrifuged (3000 rpm for 15 min) and plasma aliquots were labelled and stored at −80°C until required for analysis. As detailed previously(Reference Laird, O’Halloran and Carey5), plasma total B12 and folate concentrations were determined by microbiological assays(Reference Molloy and Scott25,Reference Kelleher and Broin26) . The inter-assay CV for plasma B12 and folate was < 10·9 %. B12 status profiles (pmol/l) were defined as follows: < 185, deficient low; 185–< 258, low normal; > 258–601, normal and > 601 high(Reference Bailey, Carmel and Green27–Reference Selhub, Jacques and Rosenberg29). Folate status profiles (nmol/l) were defined as follows: ≤ 10·0, deficient low; > 10–23·0, low normal; > 23·0–45·0, normal; > 45·0, high(Reference Selhub, Morris and Jacques30). Normal folate (> 23·0–45·0 nmol/l) and normal B12 (> 258–601) concentrations were used as the reference categories for comparison purposes.
Depressive symptoms
Depressive symptoms were assessed at wave 1 using the 20-item Center for Epidemiological Studies Depression Scale (CES-D-20). A score ≥ 16 was used to define clinically significant depressive symptoms(Reference Vilagut, Forero and Barbaglia31). Participants with depressive symptoms at wave 1 were excluded from the study. At waves 2 and 3, the 8-item Center for Epidemiological Studies Depression Scale (CES-D-8) was used to screen for depressive symptoms. The CES-D-8 was introduced in the TILDA study at waves 2 and 3, and a score of ≥ 9 on this scale was used to define clinically significant depressive symptoms at these waves(Reference Briggs, Carey and Kenny32,Reference O’Halloran, Kenny and King-Kallimanis33) . The 8-item CES-D has been validated against the 20-item scale within the TILDA cohort and has been shown to be consistent, reliable and valid(Reference Briggs, Carey and Kenny32). In terms of duration of follow-up, we only included participants who completed 4-year follow-up and excluded those who were lost to follow-up/attrition before this. We excluded participants at wave 1 with significant depressive symptoms. We did not exclude participants who did not meet criteria for depressive symptoms but were taking antidepressants as antidepressant medication is used for a range of problems beyond depression including chronic pain and anxiety and is therefore not necessarily suggestive of a diagnosis of depression.
Other covariates
CVD was defined as self-report of prior myocardial infarct, cardiac failure, angina, hypertension or cardiac arrhythmia. Self-report was also elicited for chronic disease burden, with respondents asked specifically about a history of lung disease, osteoporosis, cancer, liver disease, age-related macular degeneration, cataracts, glaucoma, arthritis, urinary incontinence, Parkinson’s disease and diabetes. Medication records were examined for antihypertensive use and antidepressant use. Medication lists were also examined directly for FA supplement use (single tablet or multi-vitamin) and for use of B12 (injection or single tablet or B12 in multi-vitamin) and coded as yes/no. Participants were a asked about physical activity within the last week, and those who were inactive for the full 7 d were defined as having low physical activity, compared with moderate (active 1–3 d) and high (active 4 or more days) physical activity. Alcohol excess was assessed through the ‘Cut down, Annoyed, Guilty, Eye-opener’ (CAGE) questionnaire, a screening tool for problematic drinking with a score equal or greater than 3 indicating an issue. This was in addition to the coding of the current smoking status of the subjects. Functional impairment was defined as impairment in one or more instrumental activities of daily living, while cognitive impairment was defined as a Mini Mental Sate Examination score ≤ 24. As described previously(Reference Briggs, McCarroll and O’Halloran20), vitamin D analysis included total plasma 25-hydroxyvitamin D (25(OH)D (D2 and D3)) concentrations which were quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS) (API 4000; AB SCIEX) and batch analysed in the Biochemistry Department of St James’s Hospital (which is accredited (ISO 15189)). As per Health and Medicine Division (formerly Institute of Medicine) guidelines, risk of vitamin D deficiency, insufficiency and sufficiency were defined as < 30, 30–50 and > 50 nmol/l, respectively(34).
Statistical analysis
Normally distributed continuous variables were described as means and standard deviations and compared using student’s t test. Categorical variables were compared using the χ 2 test. Proportional estimates were used to compare incidence of depression by folate and B12 categories. Logistic regression models reporting OR with 95 % CI were used to analyse the longitudinal association of folate and B12 categories with depression. Two models were tested: the first model was unadjusted; the second model adjusted for age, sex, BMI, alcohol, smoking status, cardiac disease, cognitive impairment, chronic disease burden, vitamin D status and antidepressant use. In order to confirm that results were not related to antidepressant use or folate or vitamin B12 supplementation, analyses were re-run excluding participants prescribed either of these medications/supplements. A P value ≤ 0·05 was considered statistically significant. Data were analysed using Stata 15 (Satatcorp).
Results
Baseline characteristics of the study population are presented in Table 1. At wave 1, a higher proportion of those classified with incident depressive symptoms were female, obese, had a higher burden of chronic and CVD and reported a higher use of antidepressant medications. Those with incident depressive symptoms had a significantly lower mean concentration of plasma folate (21·4 v. 25·1 nmol/l; P =< 0·001) and a lower mean concentration of B12 (315·7 v. 335·9 pmol/l; P = 0·014) (unadjusted) (Table 1). The mean concentrations of the proportions and status of plasma folate and B12 are displayed in Table 2. There were no significant differences in the proportions of either the folate or B12 status category by depression status (Table 2).
Baseline characteristics by incident depression status (Mean values and 95 % confidence intervals)
CAGE, Cut Down, Annoyed, Guilty, Eye Opener Alcohol Scale; I-ADL, instrumental activities of daily living; prop., proportional estimation.
Baseline characteristics of study sample by depression diagnosis. Incident depression is 8-item CES-D score 9 at either wave 2 or wave 3 (i.e. 2- or 4-year follow-up). Student’s t test used for continuous variables with adjusted Wald test post-estimation. χ 2 analysis was used for categorical variables.
* Self-reported difficulty in at least 1 instrumental ADL (i.e. shopping, housekeeping, accounting, food preparation and telephone/transportation).
† Self-report of lung disease, osteoporosis, cancer, liver disease, eye disease (age-related macular degeneration, glaucoma or cataracts), arthritis, urinary incontinence, Parkinson’s disease and diabetes.
‡ Self-report of myocardial infarction, arrhythmia, hypertension, angina or cardiac failure.
§ Mini-Mental State Examination score of ≤ 2.
Folate and vitamin B12 concentration and status by incident depression (Mean values and 95 % confidence intervals)
* Weighted population proportion.
Incident depression is 8-item CES-D score 9 at either wave 2 or wave 3 (i.e. 2- or 4-year follow-up).
Student’s t test used for continuous variables with adjusted Wald test post-estimation. χ 2 analysis was used for categorical variables.
In an unadjusted regression model with normal vitamin B12 concentration (> 258–601 pmol/l) as the reference, those with deficient-low B12 status had an increased likelihood of incident depression (OR 1·55 (95 % CI 1·07, 2·25); t = 2·32; P = 0·021) (Table 3). This finding then persisted in model 2 (OR 1·52 (95 % CI 1·05, 2·21); t = 2·25; P = 0·025) with age, sex and education and also in the fully adjusted model (OR 1·51 (95 % CI 1·01, 2·27); t = 2·03; P = 0·043) (Table 3). When vitamin B12 concentration was examined as a continuous variable (data not shown), higher concentrations (per unit increased in blood B12 concentrations) were associated with a decreased likelihood of incident depression symptoms (OR 0·99 (95 % CI 0·97, 0·99); t = –2·01; P = 0·045). In a sensitivity analysis which evaluated depressive symptoms as a continuous variable, deficient-low B12 status predicted a higher CES-D score (regression coefficient (B): 0·50; P = 0·037).
Vitamin B12 status and risk of incident depression (Odds ratios and 95 % confidence intervals)
I-ADL, instrumental activities of daily living; ref, reference value.
Logistic regression models with incident depression as dependent variable.
* Self-reported difficulty in at least 1 I-ADL (i.e. shopping, housekeeping, accounting, food preparation and telephone/transportation).
† Self-report of lung disease, osteoporosis, cancer, liver disease, eye disease (age-related macular degeneration, glaucoma or cataracts), arthritis, urinary incontinence, Parkinson’s disease and diabetes.
‡ Self-report of myocardial infarction, arrhythmia, hypertension, angina or cardiac failure.
§ Mini-Mental State Examination score of ≤ 24.
In terms of folate, there was no statistically significant difference in the likelihood of incident depressive symptoms by folate categories using normal folate status (> 23·0–45·0 nmol/l) as the reference (online Supplementary Table S1). In all models, other determinants of depressive symptoms included sex, education, chronic disease, BMI, antidepressant use at baseline, subthreshold depressive symptoms and vitamin D status as reported previously(Reference Briggs, McCarroll and O’Halloran20). When examined by the exclusion of B12-supplement/injection users and/or antidepressant medication users, the results remained consistent in both the unadjusted and fully adjusted models (Table 4). For instance, when excluding both supplements and medications, those with a deficient-low B12 status had a significantly increased risk of incident depressive symptoms (OR 1·65 (95 % CI 1·07, 2·54); P = 0·024). The results for folate did not change when those reporting antidepressant use or FA supplement use were removed from the analysis (online Supplementary Table S2).
Exclusion of antidepressants and vitamin B12 injection/supplement use and the association of vitamin B12 status with incident depression (Odds ratios and 95 % confidence intervals)
* Logistic regression models, reporting OR with 95 % CI for vitamin B12 status regressed on incident depression. Model 1 is unadjusted; model 2 controls for age, sex, educational attainment, BMI, smoking status and alcohol excess, subthreshold depressive symptoms, vitamin D, functional impairment, physical activity, chronic disease burden, CVD, cognitive impairment and antidepressant use.
Discussion
In this population representative study, we observed that those with deficient-low B12 status had a 51 % increased likelihood of developing depressive symptoms over 4 years. These findings remained consistent even after adjustment for confounders and after removing those reporting B12 supplements/injections and antidepressant users. Results from previous studies have been inconsistent regarding the association of B12 in relation with depression. In a study of 700 older community-dwelling adults (> 65 years), those with B12 deficiency (< 148 pmol/l) had a doubled risk of depression compared to subjects with normal concentrations(Reference Penninx, Guralnik and Ferrucci35). Another study in older adults observed a similar increased risk of depression with low B12 status(Reference Tiemeier, van Tuijl and Hofman13), while a further four studies in similar cohorts observed no such association(Reference Moore, Hughes and Hoey17,Reference Bjelland, Tell and Vollset36–Reference Pan, Chang and Yeh38) . Two studies have also shown a lower risk of depression with higher dietary intakes of B12 (Reference Gougeon, Payette and Morais39,Reference Skarupski, Tangney and Li40) .
Similar inconsistency has been reported in studies using B12 injections to treat depression(Reference Hvas, Juul and Lauritzen41,Reference Syed, Wasay and Awan42) , while two meta-analyses investigating B12 in relation to depression in older adults reported contradictory results(Reference Almeida, Ford and Flicker43,Reference Petridou, Kousoulis and Michelakos44) . Prospective studies have also followed a similar pattern of inconsistency. In a 2-year follow-up of 732 older Korean adults (> 65 years), low B12 concentrations were predictive for depression(Reference Kim, Stewart and Kim45). However, in a 15-year follow-up of 1012 older adults (> 65 years) from the Longitudinal Aging Study Amsterdam, serum B12 was not associated with depression(Reference Elstgeest, Brouwer and Penninx46). It is difficult to reconcile the conflicting results of studies to-date. Substantial differences across all studies include the use of different biomarkers to characterise B12 status, different tests/cut-offs to assess depression, different follow-up time periods, different confounders in statistical modelling and different food fortification or B12 supplement use/guidelines in the various international populations. Differences may have also occurred in the cut-points for B12 deficiency across studies (which adds to the comparability difficulty) and there is much debate in the literature on what cut-off to use. The current study utilised 185 pmol/l as a cut-point as it would include both frank deficiency and borderline deficiency(Reference Bailey, Carmel and Green27–Reference Selhub, Jacques and Rosenberg29). Furthermore, although 148 pmol/l is commonly used clinically for low vitamin B12 status, there is evidence that the prevalence of vitamin B12 deficiency is underestimated when using < 148 pmol/l as many individuals above that level can still exhibit clinical symptoms of deficiency(Reference Bailey, Carmel and Green27–Reference Selhub, Jacques and Rosenberg29). However, despite all these differences there is still a biological plausibility of a link between B12 and depression given that B12 is a necessary co-factor for methionine synthesis which provides methionine, the precursor of S-adenosylmethionine that is then needed for the formation of important brain neurotransmitters such as dopamine and norepinephrine(Reference Bailey, Stover and McNulty18,Reference Bottiglieri and Reynolds19) .
We observed no association of folate status with depression risk in the current study. Although mean blood folate concentrations were lower in those with incident depression, after adjusting for important covariates, folate status had no association with depression. Other factors that influenced micronutrient status in this population included obesity, medication use, smoking, wealth, sex and geographic location(Reference Laird, O’Halloran and Carey5). Our findings are consistent with other international longitudinal studies observing no such association of folate with depression risk(Reference Gougeon, Payette and Morais39,Reference Skarupski, Tangney and Li40) . Both the Quebec Longitudinal Study on Nutrition and Aging (NuAge)(Reference Gougeon, Payette and Morais39) and the Chicago Health and Aging Study(Reference Skarupski, Tangney and Li40) did not observe any association of folate with depression although dietary folate intakes and not blood concentrations were assessed. Additionally, the countries where these studies are located implement mandatory FA food fortification, and it is possible that folate could be associated with depression but only at insufficient concentrations below folate intake ranges in these populations(Reference Skarupski, Tangney and Li40). In contrast, the Trinity Ulster Department of Agriculture Ageing Cohort Study (TUDA) study did observe a positive association of folate with depression risk using erythrocyte folate (instead of plasma folate) as a marker of folate status, though the study did not control for important covariates such as vitamin D status(Reference Moore, Hughes and Hoey17). The TUDA study also observed no such association of vitamin B12 with depression after adjustment for other factors. The findings between TILDA and TUDA appear inconsistent as the two study populations were exposed to a similar background of B-vitamin intake. However, there are some key differences in the cohorts. TILDA was a nationally representative recruitment of healthy free-living persons v. specific recruitment of persons with mild to moderate age-related diseases (TUDA) in hospital or GP settings(Reference Moore, Hughes and Hoey17). Additionally, the mean age of the participants of TUDA was significantly older than TILDA and TUDA was a cross-sectional analysis v. longitudinal analysis in TILDA. Inconsistences also exist for folate in terms of international studies in relation to the different types of blood biomarker measured, different depression assessments and different policies of FA fortification across countries, again making comparative interpretations of the data difficult.
Interestingly, we observed that as age increased, the risk of incident depression decreased which has been reported previously(Reference Briggs, McCarroll and O’Halloran20). This was unrelated to vitamin B12 and folate blood concentrations as the older participants had the lowest concentrations and the highest levels of deficiency and low status(Reference Laird, O’Halloran and Carey5).
A major strength of the current research is that it is based on a large, nationally representative population sample. Additional strengths include the longitudinal design of over 4 years in a well-characterised cohort adjusting for a wide range of confounders including chronic disease, medications, lifestyle factors and other nutrient blood biomarkers which has not been attempted previously. Limitations include the fact that both folate and B12 were only measured at baseline, we did not have other biochemical measures of these micronutrients (which limits accuracy in determining blood status) and we lacked data pertaining to dietary intake of these vitamins. Depression was measured using CES-D, which is not the gold standard clinical interview, while both chronic disease and CVD conditions were self-reported which could increase the risk of response bias.
Conclusion
In conclusion, we observed that low B12 status was associated with a significantly increased risk of depressive symptoms over 4-year period in a large population representative study of older adults. No associations were observed for folate. These findings are relevant given the high occurrence of incident depression and the high levels of low-deficient status of B12 in older adults. These observations also provide reassurance for food policy makers that fortification of foods to increase levels of these vitamins could have the potential for benefits in prevention of this condition. However, future prospective studies and randomised trials using an agreed set of harmonised measures and blood biomarkers are needed to fully ascertain the utility of vitamin B12 in relation to the prevention or delay in the onset of depression in older adults.
Acknowledgements
The financial support was provided by Irish Government, the Atlantic Philanthropies and Irish Life plc. These funders had no involvement in the study design, collection, analysis and interpretation of data, writing of the paper or submission for publication. Any views expressed in this report are not necessarily those of the Department of Health and Children or of the Minister for Health.
The authors contribution are as follows: R. B., A. M. M., R. A. K. and E. J. L. designed the research; E. J. L., M. H., A. M. M. and R. B. conducted the research; B. H., D. O. C., R. B. and E. J. L. analysed the data; and all authors contributed in the final preparation of the manuscript.
The authors declare no conflicts of interest.
Supplementary material
For supplementary material referred to in this article, please visit https://doi.org/10.1017/S0007114521004748
