Mandatory fortification of the food supply with cobalamin: an idea whose time has not yet come

Homocysteine-a retrospective and prospective appraisal

The biologically important amino acid homocysteine links sulfur, methionine, and one-carbon metabolism. This review describes its initial discovery, the identification of the clinical condition of "homocystinuria" and the recognition of its close relationship to folate and vitamin B12 metabolism. It discusses the history behind its current association with diverse diseases including neural tube defects, cardio- and cerebrovascular disease and, more recently, dementia and Alzheimer's Disease. It also explores current controversies and considers potential future research directions. It is intended to give a general overview of homocysteine in relation to health and disease.

Should vitamin B12 status be considered in assessing risk of neural tube defects?

There is a strong biological premise for including vitamin B₁₂ with folic acid in strategies to prevent neural tube defects (NTDs), due to the closely interlinked metabolism of these two vitamins. For example, reduction of B₁₂ deficiency among women of reproductive age could enhance the capacity of folic acid to prevent NTDs by optimizing the cellular uptake and utilization of natural folate cofactors. Vitamin B₁₂ might also have an independent role in NTD prevention, such that adding it in fortification programs might be more effective than fortifying with folic acid alone. Globally, there is ample evidence of widespread vitamin B₁₂ deficiency in low‐ and middle‐income countries, but there is also considerable divergence of vitamin B₁₂ status across regions, likely due to genetic as well as nutritional factors. Here, I consider the evidence that low vitamin B₁₂ status may be an independent factor associated with risk of NTDs, and whether a fortification strategy to improve B₁₂ status would help reduce the prevalence of NTDs. I seek to identify knowledge gaps in this respect and specify research goals that would address these gaps.

Homocysteine-reducing B vitamins and ischemic heart disease: a separate-sample Mendelian randomization analysis

BACKGROUND/OBJECTIVES

Observationally, homocysteine is positively associated with ischemic heart disease (IHD) and unhealthy lipids; folate and vitamin B12, which reduce homocysteine, are associated with lower IHD risk and healthy lipids. Randomized controlled trials have shown no benefits of folate and vitamin B12 for IHD. To clarify the role of these potential targets of intervention in IHD we assessed how genetically determined homocysteine, folate and vitamin-B12-affected IHD and lipids.

SUBJECTS/METHODS

Separate-sample instrumental variable analysis with genetic instruments, that is, Mendelian randomization, was used to obtain unconfounded estimates (based on strongly related single-nucleotide polymorphisms (SNPs)) using CARDIoGRAMplusC4D, a large coronary artery disease/myocardial infarction (CAD/MI) case (n=64 374)-control (n=130 681) study with extensive genotyping, and the Global Lipids Genetics Consortium Results (n=196 475).

RESULTS

Homocysteine was unrelated to CAD/MI (odds ratio (OR) 1.07 per log-transformed s.d., 95% confidence interval (CI) 0.96 to 1.19) based on 14 SNPs, as was folate (OR 1.18 per s.d., 95% CI 0.80 to 1.75) based on rs153734, and vitamin B12 (OR 0.98 per log-transformed s.d., 95% CI 0.85 to 1.14) based on rs602662, rs9473555, rs526934 and rs11254363. Homocysteine and folate were not clearly associated with lipids, vitamin B12 was associated with higher inverse normal transformed low-density lipoprotein cholesterol (0.07, 95% CI 0.02 to 0.12) and triglycerides (0.05, 95% CI 0.004 to 0.09).

CONCLUSIONS

Our findings do not corroborate the observed positive association of homocysteine or negative associations of folate and vitamin B12 with CAD/MI. Vitamin B12 might be associated with an unfavorable lipid profile.

Contribution of food sources to the vitamin B12 status of South Indian children from a birth cohort recruited in the city of Mysore

OBJECTIVE

There is evidence that subclinical vitamin B12 (B12) deficiency is common in India. Vegetarianism is prevalent and therefore meat consumption is low. Our objective was to explore the contribution of B12-source foods and maternal B12 status during pregnancy to plasma B12 concentrations.

DESIGN

Maternal plasma B12 concentrations were measured during pregnancy. Children's dietary intakes and plasma B12 concentrations were measured at age 9.5 years; B12 and total energy intakes were calculated using food composition databases. We used linear regression to examine associations between maternal B12 status and children's intakes of B12 and B12-source foods, and children's plasma B12 concentrations.

SETTING

South Indian city of Mysore and surrounding rural areas.

SUBJECTS

Children from the Mysore Parthenon Birth Cohort (n 512, 47.1 % male).

RESULTS

Three per cent of children were B12 deficient (<150 pmol/l). A further 14 % had 'marginal' B12 concentrations (150-221 pmol/l). Children's total daily B12 intake and consumption frequencies of meat and fish, and micronutrient-enriched beverages were positively associated with plasma B12 concentrations (P=0.006, P=0.01 and P=0.04, respectively, adjusted for socio-economic indicators and maternal B12 status). Maternal pregnancy plasma B12 was associated with children's plasma B12 concentrations, independent of current B12 intakes (P<0.001). Milk and curd (yoghurt) intakes were unrelated to B12 status.

CONCLUSIONS

Meat and fish are important B12 sources in this population. Micronutrient-enriched beverages appear to be important sources in our cohort, but their high sugar content necessitates care in their recommendation. Improving maternal B12 status in pregnancy may improve Indian children's status.

Role of serum holotranscobalamin (holoTC) in the diagnosis of patients with low serum cobalamin. Comparison with methylmalonic acid and homocysteine

Plasma holotranscobalamin (holoTC) transports active cobalamin. Decreased levels of holoTC have been considered to be the earliest marker of cobalamin (Cbl) deficiency. In this work, holoTC was evaluated in low or borderline serum Cbl (LB12) and a concordance analysis was carried out with methylmalonic acid (MMA) and homocysteine (Hcy). Levels of Cbl, holoTC, MMA, and Hcy were investigated in a reference group in 106 patients with LB12 (≤200 pmol/l) and in 27 with folate deficiency (FOL). HoloTC levels were evaluated by an automated immunoassay (Active B12, Abbott Lab, Abbott Park, IL, USA). Lower levels of holoTC were observed in both LB12 and FOL groups (reference group vs LB12; p < 0.0001. Reference group vs FOL; p = 0.002). HoloTC levels were lower in LB12 than in FOL (p = 0.001). In LB12, concordance between Hcy and MMA was 82.1 % (chi-square test, p < 0.001; Kappa Index, 0.64, p < 0.0001). Concordance between Hcy and holoTC was 62 % (chi-square test, p = 0.006; Kappa index, 0.245, p = 0.006). Concordance between holoTC and MMA was 55.6 % (p = 0.233). Some cases with LB12 and elevated MMA did not show decreased holoTC. By contrast, MMA and Hcy were not increased in some patients with low holoTC and LB12. In conclusion, levels of holoTC were decreased in LB12 and FOL. In LB12 patients, holoTC concordance with MMA was poor. MMA/Hcy levels were not increased in a significant number of subjects with LB12 and low holoTC. This profile was found in iron deficiency. The significance of these changes remains to be clarified.

Diagnosis and management of clinical and subclinical cobalamin deficiencies: why controversies persist in the age of sensitive metabolic testing

In the past two decades, sensitive biochemical tests have uncovered cobalamin deficiency much more frequently than ever before. Almost all cases involve mild, biochemical changes without clinical manifestations (subclinical cobalamin deficiency; SCCD), whose health impact is unclear. Because the causes of SCCD are most often unknown, nonmalabsorptive, and seldom documented, controversy and confusion surround the diagnostic criteria and, inevitably, consequences and management of SCCD. To complicate matters, our grasp of the rarer clinical deficiency, usually a serious, progressive medical disease rooted in severe malabsorption, has receded as absorption testing has disappeared. Reexamining the accumulation of assumptions and misperceptions about cobalamin deficiency and distinguishing SCCD from clinical deficiency is long overdue. The biology of cobalamin provides an important starting point: cobalamin stores exceed daily losses so greatly and binding proteins regulate absorption so effectively that deficiency typically achieves clinical expression only after years of severe, relentless malabsorption. Dietary insufficiency, mild, partial malabsorption, and other incomplete, intermittent causes can usually produce only SCCD. Thus, the most fundamental difference between the two deficiencies is the relentlessness of the underlying cause, which determines prognosis and health impact. Inattention to absorptive status has exacerbated the limitations of biochemical testing. All the biochemical tests are highly sensitive but specificity is poor, no diagnostic gold standard exists, and diagnostic cutpoints fluctuate excessively. To limit the adverse diagnostic consequences, the diagnosis of SCCD, whose need for treatment is unclear, should be deferred unless at least two tests are abnormal. Indeed, cobalamin biology indicates that the absorption system, while enhancing cobalamin delivery, also sets a strict upper limit on it, which suggests that cobalamin excess is undesirable. Solving cobalamin deficiency requires balanced assessment of the different imperatives of clinical and public health concerns, better rationalization of diagnostic testing, consistent definitions of normality in relation to SCCD, and rational cutpoint selection.

Laboratory evaluation for vitamin B12 deficiency: the case for cascade testing

OBJECTIVE

Potential vitamin B(12) deficiency is a common clinical diagnostic problem, and many providers have a low threshold for initiating therapy. The goal of this study was to systematically evaluate current practice patterns regarding the laboratory evaluation of suspected vitamin B(12) deficiency.

METHODS

This retrospective study reviewed the electronic medical records of 192 patients initiated on intramuscular vitamin B(12) injections.

RESULTS

Only 12 patients had objectively documented hematologic responses: decrease of mean corpuscular volume by ≥5 fL with stable or improved hemoglobin. Another 5 patients had equivocal hematologic responses. There was one plausible neurologic response. Thus, only 18 (9.4%) of 192 patients had data supportive of a clinical response. In these 18 patients, the baseline serum B(12) level was ≤107 pg/mL; only 3 patients also had a baseline serum methylmalonic acid level, which was ≥1.29 μmol/L in all 3 patients.

CONCLUSIONS

Currently, only a small minority of patients initiated on intramuscular vitamin B(12) supplementation derive any meaningful clinical benefit. Furthermore, current testing recommendations for vitamin B(12) deficiency are usually not followed. Up-front ordering of a diagnostic testing cascade is recommended to improve compliance; an example is presented with decision points chosen to improve specificity for clinically evident vitamin B(12) deficiency without loss of sensitivity. Ultimately, a better understanding of vitamin B(12) physiology is needed to develop and evaluate laboratory tests that more accurately reflect true intracellular vitamin B(12) status.

Strategies to improve diet in older adults

It is estimated that by 2050 there will be 2 billion people aged 60 years and older in the world. The evidence base for the health benefits of good nutrition and physical activity, as well as weight loss among overweight and obese adults, is growing and a number of policies and guidelines are available to guide health professionals in serving older people at various stages of the lifecycle. There are many potential influences on dietary habits including individual factors, families and friends, community characteristics, the food and supplement industry, and public policy. This review focuses on the evidence base for factors influencing diet in older adults, food insecurity, Na, vitamin D, vitamin B12, protein, obesity and the benefits of energy restriction in overweight and obese older adults. Research is needed to continue to increase the evidence base for appropriate ways to improve diet and health in older people. Also, much of the available information is from the US, so there is a need to conduct research in other areas of the world.

Subclinical cobalamin deficiency

PURPOSE OF REVIEW

This review focuses on recent developments and controversies in the diagnosis, consequences, and management of subclinical cobalamin deficiency (SCCD), which affects many elderly persons.

RECENT FINDINGS

Diagnosis of SCCD depends exclusively on biochemical tests whose individual limitations suggest that combinations of tests are needed, especially in epidemiologic research. The causes of SCCD are unknown in more than 60% of cases, which limits prognostic predictions and identification of health consequences. After years of varying, often inconclusive associations, new clinical trials suggest that homocysteine reduction by high doses of folic acid, cobalamin, and pyridoxine may reduce progression of structural brain changes and cognitive impairment, especially in predisposed individuals. The causative or contributory roles, if any, of SCCD itself in cognitive dysfunction require direct study. If the findings are confirmed, high-dose supplementation with three vitamins will probably be more effective than fortification of the diet.

SUMMARY

The story of SCCD, which is severalfold times more common in the elderly than clinical cobalamin deficiency but also differs from it in arising only infrequently from severe malabsorption and thus being less likely to progress, continues to evolve. Preventive benefits need to be confirmed and expanded, and will require fuller understanding of SCCD pathophysiology, natural history, and health consequences.

Association of biochemical B₁₂ deficiency with metformin therapy and vitamin B₁₂ supplements: the National Health and Nutrition Examination Survey, 1999-2006

OBJECTIVE

To describe the prevalence of biochemical B(12) deficiency in adults with type 2 diabetes taking metformin compared with those not taking metformin and those without diabetes, and explore whether this relationship is modified by vitamin B(12) supplements.

RESEARCH DESIGN AND METHODS

Analysis of data on U.S. adults ≥50 years of age with (n = 1,621) or without type 2 diabetes (n = 6,867) from the National Health and Nutrition Examination Survey (NHANES), 1999-2006. Type 2 diabetes was defined as clinical diagnosis after age 30 without initiation of insulin therapy within 1 year. Those with diabetes were classified according to their current metformin use. Biochemical B(12) deficiency was defined as serum B(12) concentrations ≤148 pmol/L and borderline deficiency was defined as >148 to ≤221 pmol/L.

RESULTS

Biochemical B(12) deficiency was present in 5.8% of those with diabetes using metformin compared with 2.4% of those not using metformin (P = 0.0026) and 3.3% of those without diabetes (P = 0.0002). Among those with diabetes, metformin use was associated with biochemical B(12) deficiency (adjusted odds ratio 2.92; 95% CI 1.26-6.78). Consumption of any supplement containing B(12) was not associated with a reduction in the prevalence of biochemical B(12) deficiency among those with diabetes, whereas consumption of any supplement containing B(12) was associated with a two-thirds reduction among those without diabetes.

CONCLUSIONS

Metformin therapy is associated with a higher prevalence of biochemical B(12) deficiency. The amount of B(12) recommended by the Institute of Medicine (IOM) (2.4 μg/day) and the amount available in general multivitamins (6 μg) may not be enough to correct this deficiency among those with diabetes.