Vitamin B-12 and cognition in the elderly

DTI correlates of cognition in conventional MRI of normal-appearing brain in patients with clinical features of subacute combined degeneration and biochemically proven vitamin B(12) deficiency

BACKGROUND AND PURPOSE

Vitamin B12 deficiency may cause neural injury that results in cognitive deficits. The main purpose of our study was to evaluate morphometric and microstructural changes in the brain and relate them to cognition in subacute combined degeneration of the spinal cord and patients with biochemically deficient vitamin B12.

MATERIALS AND METHODS

Fifty-one patients were recruited and underwent nerve-conduction velocity tests and routine hematologic examinations. Serum vitamin B12 and homocystine levels were also measured. All patients and 46 age- and sex-matched controls underwent cervical spine and brain MR imaging along with cognition tests. MR imaging included conventional scans and DTI. Voxel-based morphometry was performed for determining the WM and GM volumes, based on T1-weighted images. DTI measures that included fractional anisotropy, ADC, radial diffusivity, and axial diffusivity were determined by using tract-based statistics.

RESULTS

None of the patients showed any abnormality on conventional MR imaging. No significant changes in GM and WM volumes were observed in patients compared with controls. Significant reductions in the fractional anisotropy and an increase in ADC and radial diffusivity values were observed in multiple brain regions in patients compared with controls. These changes were confirmed on the region-of-interest analysis. Neuropsychological scores were significantly different in patients compared with controls and showed significant correlation with fractional anisotropy and radial diffusivity in a few brain regions.

CONCLUSIONS

Microstructural changes are seen in WM regions on DTI in patients with vitamin B12 deficiency and correlate with cognition scores. DTI can be used for objective assessment of microstructural changes in the brain in vitamin B12 deficiency.

Interactions between plasma concentrations of folate and markers of vitamin B(12) status with cognitive performance in elderly people not exposed to folic acid fortification: the Hordaland Health Study

A combination of high folate with low vitamin B12 plasma status has been associated with cognitive impairment in a population exposed to mandatory folic acid fortification. The objective of the present study was to examine the interactions between plasma concentrations of folate and vitamin B12 markers in relation to cognitive performance in Norwegian elderly who were unexposed to mandatory or voluntary folic acid fortification. Cognitive performance was assessed by six cognitive tests in 2203 individuals aged 72-74 years. A combined score was calculated using principal component analysis. The associations of folate concentrations, vitamin B12 markers (total vitamin B12, holotranscobalamin (holoTC) and methylmalonic acid (MMA)) and their interactions in relation to cognitive performance were evaluated by quantile regression and least-squares regression, adjusted for sex, education, apo-ɛ4 genotype, history of CVD/hypertension and creatinine. Cross-sectional analyses revealed an interaction (P= 0·009) between plasma concentrations of folate and vitamin B12 in relation to cognitive performance. Plasma vitamin B12 concentrations in the lowest quartile ( < 274 pmol/l) combined with plasma folate concentrations in the highest quartile (>18·5 nmol/l) were associated with a reduced risk of cognitive impairment compared with plasma concentrations in the middle quartiles of both vitamins (OR 0·22, 95 % CI 0·05, 0·92). The interaction between folate and holoTC or MMA in relation to cognitive performance was not significant. In conclusion, this large study population unexposed to mandatory folic acid fortification showed that plasma folate, but not plasma vitamin B12, was associated with cognitive performance. Among the elderly participants with vitamin B12 concentrations in the lower range, the association between plasma folate and cognitive performance was strongest.

Water-soluble vitamins in people with low glomerular filtration rate or on dialysis: a review

People with low glomerular filtration rate and people on dialysis are spontaneously at risk for vitamin deficiency because of the potential for problems with decreased appetite and decreased sense of smell and taste, leading to decreased intake, and because decreased energy or decreased cognitive ability results in difficulties in shopping and cooking. Imposed dietary restrictions because of their renal dysfunction and because of comorbidities such as hypertension and diabetes exacerbate this problem. Finally, particularly for water-soluble vitamins, loss may occur into the dialysate. We did not identify any randomized trials of administering daily doses close to the recommended daily allowances of these vitamins. In people who are eating at all, deficiencies of B5 and B7 seem unlikely. It is unclear whether supplements of B2 and B3 are necessary. Because of dialyzability and documented evidence of insufficiency in dialysis patients, B1 supplementation is likely to be helpful. B6, B9, and B12 are implicated in the hyperhomocysteinemia observed in patients on dialysis. These vitamins have been studied in combinations, in high doses, with the hope of reducing cardiovascular outcomes. No reductions in patient-important outcomes were seen in adequately powered randomized trials. Because of their involvement in the homocysteine pathway, however, supplementation with lower doses, close to the recommended daily allowances, may be helpful. Vitamin C deficiency is common in patients on dialysis who are not taking supplements: low-dose supplements are warranted. Vitamins for dialysis patients contain most or all of the B vitamins and low-dose vitamin C. We are not aware of any medical reasons to choose one over another.

Biochemical markers of vitamin B12 deficiency combined in one diagnostic parameter: the age-dependence and association with cognitive function and blood hemoglobin

BACKGROUND

Vitamin B12 deficiency is diagnosed by measurements of total B12, holo-transcobalamin (holoTC), methylmalonic acid (MMA) and total homocysteine (Hcy) in blood. Results of the individual biochemical tests are often contradictory. Here the four markers are combined to achieve a more reliable indication of the B12 status. The results are aligned with hemoglobin and cognitive score.

METHODS

Databases from the literature were plotted in coordinates x=(holoTC·B12)(1∕2), y=1∕2·log10(MMA·Hcy), where distribution of points revealed the subgroups characterized by logarithmic ratios lr=log10[(holoTC·B12)/(MMA·Hcy)]. Distance between the subgroups w=lr(Test)-lr(Normal) was taken as a robust biochemical indicator of B12 status ("wellness parameter").

RESULTS

The dependence of lr(Normal) vs. age was described by a mathematical function to correct parameter w. The B12 status was defined as "excellent" (w≈+0.4), "normal" (w≈0), "transitional" (w≈-0.5), "deficient" (w≈-1.7) and "pernicious" (w≈-3.0). The groups of individuals with either w≥0 or w≤-1 exhibited the statistically significant differences in both hemoglobin and cognitive score. Analogous assessment of B12 status by the individual markers agreed with only one out of two physiological characteristics.

CONCLUSION

Combined parameter w is a reliable diagnostic tool.

Cobalamin and folate status predicts mental development scores in North Indian children 12-18 mo of age

BACKGROUND

Micronutrient deficiencies can affect cognitive function. Many young children in low- and middle-income countries have inadequate cobalamin (vitamin B-12) status.

OBJECTIVE

The objective was to measure the association of plasma concentrations of folate, cobalamin, total homocysteine, and methylmalonic acid with cognitive performance at 2 occasions, 4 mo apart, in North Indian children aged 12-18 mo.

DESIGN

Bayley Scales of Infant Development II were used to assess cognition. In multiple regression models adjusted for several potential confounders, we measured the association between biomarkers for folate and cobalamin status and psychomotor or mental development scores on the day of blood sampling and 4 mo thereafter.

RESULTS

Each 2-fold increment in plasma cobalamin concentration was associated with a significant increment in the mental development index score of 1.3 (95% CI: 0.2, 2.4; P = 0.021). Furthermore, each 2-fold increment in homocysteine or methylmalonic acid concentration was associated with a decrement in mental development index score of 2.0 (95% CI: 0.5, 3.4; P = 0.007) or 1.1 (95% CI: 0.3, 1.8; P = 0.004) points, respectively. Plasma folate concentration was significantly and independently associated with mental development index scores only when children with poor cobalamin status were excluded, ie, in those who had cobalamin concentrations below the 25th percentile. None of these markers was associated with psychomotor scores in the multiple regression models.

CONCLUSIONS

Cobalamin and folate status showed a statistically significant association with cognitive performance. Given the high prevalence of deficiencies in these nutrients, folate and cobalamin supplementation trials are required to measure any beneficial effect on cognition.

Cognitive function in an elderly population: interaction between vitamin B12 status, depression, and apolipoprotein E ε4: the Hordaland Homocysteine Study

OBJECTIVE

To investigate the cross-sectional relation between metabolic markers of vitamin B(12) status and cognitive performance, and possible effect modification by the presence of depression and apolipoprotein E (ApoE) ε4.

METHODS

This is a population-based study of 1935 participants, aged 71 to 74 years, from Norway. Participants were administered a cognitive test battery, and vitamin B(12) status was assessed by measurements of plasma vitamin B(12), holotranscobalamin (holoTC), methylmalonic acid (MMA), and total homocysteine.

RESULTS

The geometric mean (95% confidence interval) for vitamin B(12) was 348 pM (341-354), whereas 5.9% of participants had vitamin B(12) levels lower than 200 pM. In linear regression analyses, holoTC (p = .039) and the holoTC/vitamin B(12) ratio (p = .013) were positively related, whereas MMA (p = .010) was inversely related, to global cognition, after adjustment for sex, education, ApoE status, plasma creatinine, and history of diabetes, cardiovascular disease, hypertension, and depression. Among those positive for ApoE ε4, but not among those without the ε4 allele, plasma vitamin B(12) was positively associated with global cognition (p = .015), whereas MMA was inversely related to global cognition (p = .036) and executive function (p = .014). In participants with depression, MMA was inversely associated with global cognition (p < .001) and episodic memory (p = .001).

CONCLUSIONS

Among the well-nourished elderly, low vitamin B(12) status is associated with cognitive deficit, particularly in those with the ApoE ε4 allele or with depression.

Remission of cognitive deficits in Parkinson's disease: recovery from a nonamnestic mild cognitive impairment or psychiatric symptoms remission?

Mild cognitive impairment is a clinical condition more frequent in patients with Parkinson's disease than in general population. The nonamnestic presentations, usually characterized by executive dysfunction, are most prevalent. We present a case report of a Parkinson's disease patient diagnosed with nonamnestic mild cognitive impairment that showed complete remission of cognitive symptoms after one year. We discuss the possible causes for the remission, focusing on the treatment of medical conditions such as a major depressive episode and vitamin B12 deficiency, in addition to the change of pharmacological treatment. In a third assessment, cognitive performance remained normal. The case report highlights the importance of controlling clinical comorbidities on the assessment and followup of mild cognitive impairment, especially on Parkinson's disease.

Maternal vitamin C deficiency during pregnancy persistently impairs hippocampal neurogenesis in offspring of guinea pigs

While having the highest vitamin C (VitC) concentrations in the body, specific functions of VitC in the brain have only recently been acknowledged. We have shown that postnatal VitC deficiency in guinea pigs causes impairment of hippocampal memory function and leads to 30% less neurons. This study investigates how prenatal VitC deficiency affects postnatal hippocampal development and if any such effect can be reversed by postnatal VitC repletion. Eighty pregnant Dunkin Hartley guinea pig dams were randomized into weight stratified groups receiving High (900 mg) or Low (100 mg) VitC per kg diet. Newborn pups (n = 157) were randomized into a total of four postnatal feeding regimens: High/High (Control); High/Low (Depleted), Low/Low (Deficient); and Low/High (Repleted). Proliferation and migration of newborn cells in the dentate gyrus was assessed by BrdU labeling and hippocampal volumes were determined by stereology. Prenatal VitC deficiency resulted in a significant reduction in postnatal hippocampal volume (P<0.001) which was not reversed by postnatal repletion. There was no difference in postnatal cellular proliferation and survival rates in the hippocampus between dietary groups, however, migration of newborn cells into the granular layer of the hippocampus dentate gyrus was significantly reduced in prenatally deficient animals (P<0.01). We conclude that a prenatal VitC deficiency in guinea pigs leads to persistent impairment of postnatal hippocampal development which is not alleviated by postnatal repletion. Our findings place attention on a yet unrecognized consequence of marginal VitC deficiency during pregnancy.

Associations between serum homocysteine, holotranscobalamin, folate and cognition in the elderly: a longitudinal study

OBJECTIVES

To examine the associations between serum homocysteine (tHcy), holotranscobalamin (holoTC, the biologically active fraction of vitamin B12) and folate and cognitive functioning in a longitudinal population-based study of Finnish elderly subjects.

SUBJECTS AND DESIGN

tHcy, holoTC and folate were measured at baseline in 274 dementia-free subjects aged 65-79years from the Cardiovascular Risk Factors, Aging and Dementia study. Subjects were re-examined 7years later, and global cognition, episodic memory, executive functioning, verbal expression and psychomotor speed were assessed.

RESULTS

Higher baseline tHcy levels were associated with poorer performance in global cognition, relative difference: 0.90 [95% confidence interval (CI) 0.81-0.99]; episodic memory: 0.87 (95% CI 0.77-0.99); executive functions: 0.86 (95% CI 0.75-0.98); and verbal expression: 0.89 (95% CI 0.81-0.97) at follow-up. Increased holoTC levels were related to better performance on global cognition: 1.09 (95% CI 1.00-1.19); executive functions: 1.11 (95% CI 1.01-1.21); and psychomotor speed: 1.13 (95% CI 1.01-1.26). After excluding 20 cases of incident dementia, increased tHcy remained associated with poorer performance in episodic memory, execution functions and verbal expression. Higher holoTC levels tended to be related to better performance in executive functions and psychomotor speed, while elevated serum folate concentrations were significantly related to higher scores in global cognition and verbal expression tests.

CONCLUSIONS

tHcy, holoTC and folate levels are related to cognitive performance 7years later even in nondemented elderly subjects. Randomized trials are needed to determine the impact of vitamin B12 and folate supplementation on preventing cognitive decline in the elderly.

Increased Vitamin B12 levels are associated with mortality in critically ill medical patients

BACKGROUND & AIMS

We describe an observational study in critically ill medical patients showing the association between serum Vitamin B12 levels measured on or near admission and the outcome in these patients.

METHODS

We used the database of patients admitted to the Medical Intensive Care Unit (MICU) at the Hadassah-Hebrew University Medical Center in Jerusalem, Israel, to analyze associations between patient demographics, background, diagnoses and serum Vitamin B12 levels with hospital and 90 day outcomes.

RESULTS

Higher mean Vitamin B12 levels were found in patients who did not survive their hospital stay (1719 pg/ml vs 1003 pg/ml, p < 0.01). Those who had died by 90 days after admission to the MICU also had higher Vitamin B12 levels than survivors (1593 pg/ml vs 990 pg/ml). Regression analysis showed that elevated Vitamin B12 levels were associated with increased 90 day mortality, even after controlling for other variables. Survival analysis also showed an increased mortality rate in patients with Vitamin B12 levels over 900 pg/ml (p < 0.0002).

CONCLUSIONS

Our data show that high serum Vitamin B12 levels are associated with increased mortality in critically ill medical patients. We suggest that Vitamin B12 levels should be included in the work-up of all medical intensive care patients, particularly those with a chronic health history and increased severity of illness.

Cognitive function after supplementation with B vitamins and long-chain omega-3 fatty acids: ancillary findings from the SU.FOL.OM3 randomized trial

BACKGROUND

Rapid aging of the population worldwide necessitates a heightened concern about preventing cognitive decline.

OBJECTIVE

We investigated the effects of B vitamins and omega-3 (n-3) fatty acid supplementation on cognition in a high-risk population.

DESIGN

This was an ancillary study of the SU.FOL.OM3 (SUpplementation with FOLate, vitamins B-6 and B-12 and/or OMega-3 fatty acids) secondary prevention trial conducted in France between 2003 and 2009. The present sample included 1748 men and women aged 45-80 y with a history of myocardial infarction, unstable angina, or ischemic stroke and who were recruited via a network of 417 physicians. With the use of block randomization with stratification by sex, age, prior cardiovascular disease, and city of residence, participants were assigned in a 2 × 2 factorial design to 1 of 4 groups: 1) 5-methyltetrahydrofolate (folate, 0.56 mg) and vitamins B-6 (3 mg) and B-12 (0.02 mg), 2) eicosapentaenoic and docosahexaenoic acids (600 mg) in a 2:1 ratio, 3) B vitamins and omega-3 fatty acids, or 4) placebo. Cognitive function after 4 y of supplementation was assessed with the French version of the modified Telephone Interview for Cognitive Status.

RESULTS

No significant main effects of group assignment on cognitive function were found; however, we found some evidence of disease history- and age-specific effects. In the subgroup with prior stroke, for example, participants assigned to receive B vitamins plus omega-3 fatty acids were significantly less likely to have a decreased score on the temporal orientation task than were those assigned to receive placebo (odds ratio: 0.43; 95% CI: 0.21, 0.86).

CONCLUSIONS

If present, dietary effects on cognition are likely group-specific. These results could be useful in interventions aimed at preventing cognitive decline in high-risk individuals. This trial is registered at controlled-trials.com as ISRCTN41926726.

Biomarkers of cobalamin (vitamin B12) deficiency and its application

Cobalamin (vitamin B12) deficiency in the elderly is an under recognized problem in daily clinical practice. It seems to be important because the deficiency of this vitamin can lead to irreversible neurological damage, anemia, osteoporosis, and cerebrovascular and cardiovascular diseases. Some clinical abnormalities that we thought were related to the normal aging changes may actually be caused by cobalamin deficiency, such as lack of ankle jerk reflex. The prevalence of cobalamin deficiency increases with age (ranges from 0.6% to 46% depending on the population studies and criteria for diagnosis). Other than clinical manifestations, there are some biomarkers for detection of cobalamin deficiency: the red blood cell mean corpuscular volume (MCV); serum cobalamin level; plasma holotranscobalamin; serum methylmalonic acid (MMA) levels and serum homocysteine levels. The interpretation and the application of these biomarkers are here presented.

Is a low blood level of vitamin B12 a cardiovascular and diabetes risk factor? A systematic review of cohort studies

PURPOSE

To assess the prior hypothesis that low blood vitamin B12, partly through hyperhomocysteinemia and partly through direct effects, increases the risk of cardiovascular diseases and diabetes. As background, we also extracted all-cause mortality from the studies that met our criteria.

METHODS

A systematic review of prospective cohort studies identified through searching six electronic databases, screening of reference lists, and citation search. Included studies reported data on the association between vitamin B12 blood levels, or other appropriate surrogate biological markers e.g. holotranscobalamin or serum/urine methylmalonic acid, and fatal or non-fatal incident diabetes and cardiovascular events.

RESULTS

Seven studies were included. Studies differed regarding the population studied, length of follow-up, study outcomes, and data analysis--a narrative synthesis approach was performed to examine the results. Most studies met few of the quality assessment criteria which were adapted from the Scottish Intercollegiate Guidelines Network (SIGN). Only one high-quality study reported that low B12 increased the risk of incident cerebral ischaemia (RR = 1.76; 95% CI = 1.16-2.68). After controlling for homocysteine, the association persisted although weakened (RR = 1.57; 95% CI = 1.02-2.43), suggesting that the effects of low B12 were only partly mediated by homocysteine. In two studies, higher B12 levels were associated with a greater risk of total mortality (RR = 1.00; 95% CI = 1.00-1.00 and HR = 1.15; 95% CI = 1.08-1.22, respectively) and combined fatal and non-fatal coronary events (RR = 1.00; 95% CI = 1.00-1.00). No association between study outcomes and vitamin B12 levels was found in four other studies.

CONCLUSIONS

Surprisingly, there is only very limited evidence that vitamin B12 deficiency predisposes to the risk of mortality and morbidity from either cardiovascular diseases or diabetes in adults. Current data do not support vitamin B12 supplementation to reduce the risk of cardiovascular diseases or diabetes.

Vitamin B12 in health and disease

Vitamin B(12) is essential for DNA synthesis and for cellular energy production.This review aims to outline the metabolism of vitamin B(12), and to evaluate the causes and consequences of sub-clinical vitamin B(12) deficiency. Vitamin B(12) deficiency is common, mainly due to limited dietary intake of animal foods or malabsorption of the vitamin. Vegetarians are at risk of vitamin B(12) deficiency as are other groups with low intakes of animal foods or those with restrictive dietary patterns. Malabsorption of vitamin B(12) is most commonly seen in the elderly, secondary to gastric achlorhydria. The symptoms of sub-clinical deficiency are subtle and often not recognized. The long-term consequences of sub-clinical deficiency are not fully known but may include adverse effects on pregnancy outcomes, vascular, cognitive, bone and eye health.

Vitamin B12-impaired metabolism produces apoptosis and Parkinson phenotype in rats expressing the transcobalamin-oleosin chimera in substantia nigra

BACKGROUND

Vitamin B12 is indispensable for proper brain functioning and cytosolic synthesis of S-adenosylmethionine. Whether its deficiency produces effects on viability and apoptosis of neurons remains unknown. There is a particular interest in investigating these effects in Parkinson disease where Levodopa treatment is known to increase the consumption of S-adenosylmethionine. To cause deprivation of vitamin B12, we have recently developed a cell model that produces decreased synthesis of S-adenosylmethionine by anchoring transcobalamin (TCII) to the reticulum through its fusion with Oleosin (OLEO).

METHODOLOGY

Gene constructs including transcobalamin-oleosin (TCII-OLEO) and control constructs, green fluorescent protein-transcobalamin-oleosin (GFP-TCII-OLEO), oleosin-transcobalamin (OLEO-TCII), TCII and OLEO were used for expression in N1E-115 cells (mouse neuroblastoma) and in substantia nigra of adult rats, using a targeted transfection with a Neurotensin polyplex system. We studied the viability and the apoptosis in the transfected cells and targeted tissue. The turning behavior was evaluated in the rats transfected with the different plasmids.

PRINCIPAL FINDINGS

The transfection of N1E-115 cells by the TCII-OLEO-expressing plasmid significantly affected cell viability and increased immunoreactivity of cleaved Caspase-3. No change in propidium iodide uptake (used as a necrosis marker) was observed. The transfected rats lost neurons immunoreactive to tyrosine hydroxylase. The expression of TCII-OLEO was observed in cells immunoreactive to tyrosine hydroxylase of the substantia nigra, with a superimposed expression of cleaved Caspase-3. These cellular and tissular effects were not observed with the control plasmids. Rats transfected with TCII-OLEO expressing plasmid presented with a significantly higher number of turns, compared with those transfected with the other plasmids.

CONCLUSIONS/SIGNIFICANCE

In conclusion, the TCII-OLEO transfection was responsible for apoptosis in N1E-115 cells and rat substantia nigra and for Parkinson-like phenotype. This suggests evaluating whether vitamin B12 deficit could aggravate the PD in patients under Levodopa therapy by impairing S-adenosylmethionine synthesis in substantia nigra.

Advances in the understanding of cobalamin assimilation and metabolism

The haematological and neurological consequences of cobalamin deficiency define the essential role of this vitamin in key metabolic reactions. The identification of cubilin-amnionless as the receptors for intestinal absorption of intrinsic factor-bound cobalamin and the plasma membrane receptor for cellular uptake of transcobalamin bound cobalamin have provided a clearer understanding of the absorption and cellular uptake of this vitamin. As the genes involved in the intracellular processing of cobalamins and genetic defects of these pathways are identified, the metabolic disposition of cobalamins and the proteins involved are being recognized. The synthesis of methylcobalamin and 5'-deoxyadenosylcobalamin, their utilization in conjunction with methionine synthase and methylmalonylCoA mutase, respectively, and the metabolic consequences of defects in these pathways could provide insights into the clinical presentation of cobalamin deficiency.

Is it time for vitamin B-12 fortification? What are the questions?

Since the introduction of folic acid fortification of flour 10 y ago, an initiative to consider fortifying flour with vitamin B-12 has gained momentum in the United States. The impetus for this move stems from several considerations, including some evidence that a proportion of neural tube defect pregnancies may be the result of vitamin B-12 rather than folate deficiency. However, no interventional trials have taken place to show the efficacy of vitamin B-12 supplementation or fortification in the primary prevention or recurrence of neural tube defect pregnancies, as was the case with folic acid. Other reasons put forward for the institution of vitamin B-12 fortification include the high prevalence of vitamin B-12 deficiency in certain demographic groups, including the elderly and the young in some countries. Much of this deficiency, however, is subclinical and not associated with manifest morbidity. Moreover, individuals affected by the most severe cases of vitamin B-12 deficiency that are associated with morbidity would not benefit from the concentrations of vitamin B-12 fortification that are practical or that are being considered, because such individuals suffer from malabsorption of vitamin B-12 rather than from an inadequacy of intake of the vitamin. In addition to the well-recognized complications of vitamin B-12 deficiency, such as macrocytic anemia and neurological complications affecting sensory and motor function, more subtle effects have also been described, including osteopenia, neurocognitive impairment, and increased vascular disease risk associated with elevated homocysteine. This analysis focuses on the research questions that are pertinent to the consideration of whether or not to introduce mandatory vitamin B-12 fortification in the United States.

How common is vitamin B-12 deficiency?

In considering the vitamin B-12 fortification of flour, it is important to know who is at risk of vitamin B-12 deficiency and whether those individuals would benefit from flour fortification. This article reviews current knowledge of the prevalence and causes of vitamin B-12 deficiency and considers whether fortification would improve the status of deficient subgroups of the population. In large surveys in the United States and the United Kingdom, approximately 6% of those aged > or =60 y are vitamin B-12 deficient (plasma vitamin B-12 < 148 pmol/L), with the prevalence of deficiency increasing with age. Closer to 20% have marginal status (plasma vitamin B-12: 148-221 pmol/L) in later life. In developing countries, deficiency is much more common, starting in early life and persisting across the life span. Inadequate intake, due to low consumption of animal-source foods, is the main cause of low serum vitamin B-12 in younger adults and likely the main cause in poor populations worldwide; in most studies, serum vitamin B-12 concentration is correlated with intake of this vitamin. In older persons, food-bound cobalamin malabsorption becomes the predominant cause of deficiency, at least in part due to gastric atrophy, but it is likely that most elderly can absorb the vitamin from fortified food. Fortification of flour with vitamin B-12 is likely to improve the status of most persons with low stores of this vitamin. However, intervention studies are still needed to assess efficacy and functional benefits of increasing intake of the amounts likely to be consumed in flour, including in elderly persons with varying degrees of gastric atrophy.

Vitamin B-12 and neural tube defects: the Canadian experience

Although early epidemiologic studies showed a protective effect of adequate maternal folic acid (FA) status against neural tube defects (NTDs), the role of adequate vitamin B-12 nutrition in the putative reduction of NTD frequency has remained uncertain. Evaluating vitamin B-12 status was complicated by the need to control for altered FA status after fortification in Canada. More recent studies have made use of better biomarkers of vitamin B-12 status, including methylmalonic acid and holotranscobalamin (holoTC). HoloTC provides a useful measure of vitamin B-12 status because it represents the bioavailable fraction of circulating vitamin B-12. By assessing bioavailable vitamin B-12 status in a large Canadian cohort accrued before and after FA fortification, we found a 3-fold increase in the risk of NTDs in mothers who had vitamin B-12 status in the lower quartile, regardless of FA fortification. Our work suggests that vitamin B-12 fortification, analogous to the FA fortification program, may reduce NTDs more than FA fortification alone. A multicenter randomized controlled trial comparing periconceptional vitamin B-12 in combination with FA against FA alone is warranted.

Folate-vitamin B-12 interaction in relation to cognitive impairment, anemia, and biochemical indicators of vitamin B-12 deficiency

Previous reports on pernicious anemia treatment suggested that high folic acid intake adversely influences the natural history of vitamin B-12 deficiency, which affects many elderly individuals. However, experimental investigation of this hypothesis is unethical, and the few existing observational data are inconclusive. With the use of data from the 1999-2002 National Health and Nutrition Examination Survey (NHANES), we evaluated the interaction between high serum folate and low vitamin B-12 status [ie, plasma vitamin B-12 < 148 pmol/L or methylmalonic acid (MMA) > 210 nmol/L] with respect to anemia and cognitive impairment. With subjects having both plasma folate < or = 59 nmol/L and normal vitamin B-12 status as the referent category, odds ratios for the prevalence of anemia compared with normal hemoglobin concentration and impaired compared with unimpaired cognitive function were 2.1 (95% CI: 1.1, 3.7) and 1.7 (95% CI: 1.01, 2.9), respectively, for those with low vitamin B-12 status but normal serum folate and 4.9 (95% CI: 2.3, 10.6) and 5.0 (95% CI: 2.7, 9.5), respectively, for those with low vitamin B-12 status and plasma folate >59 nmol/L. Among subjects with low vitamin B-12 status, mean circulating vitamin B-12 was 228 pmol/L for the normal-folate subgroup and 354 pmol/L for the high-folate subgroup. We subsequently showed increases in circulating homocysteine and MMA concentrations with increasing serum folate among NHANES participants with serum vitamin B-12 < 148 pmol/L, whereas the opposite trends occurred among subjects with serum vitamin B-12 > or = 148 pmol/L. These interactions, which were not seen in NHANES III before fortification, imply that, in vitamin B-12 deficiency, high folate status is associated with impaired activity of the 2 vitamin B-12-dependent enzymes, methionine synthase and MMA-coenzyme A mutase.