Folate and Vitamin B12 Status in the Americas

There is growing interest in the potential for folic acid fortification in the Americas and recognition of the high prevalence of low plasma vitamin B₁₂ concentrations reported in various studies. This review summarized available data on plasma vitamin B₁₂ and folate concentrations in the Americas. At least 40% of individuals had deficient or marginal plasma vitamin B₁₂ concentrations in almost all locations and across age groups. Low plasma folate concentrations were less common. It is hypothesized that vitamin B₁₂ deficiency may result from a low intake of animal source foods, while a higher intake of refined flour may result in low plasma folate.     

Folate and Vitamin B12 Recommended Intakes and Status in the United States

This paper presents a synopsis of the Institute of Medicine (IOM) Dietary Reference Intakes (DRIs) for folate and the recommended folic acid intake to reduce the risk of neural tube defects. Estimated intake of folic acid is presented and total folate intake is compared to the DRI. Vitamin B₁₂ DRIs are highlighted in addition to the IOM recommendation for crystalline vitamin B₁₂ intake specifically for individuals ≥57 years of age. Recently reported evidence of vitamin B₁₂ inadequacy in the aging segment of the U.S. population will be addressed.     

SERUM VITAMIN B12 BINDERS AND HUMAN MARROW CELL UPTAKE OF 57Co-VITAMIN B12

The recently-described third plasma binder (TC III) of vitamin B₁₂ is thought to originate in the granulocytes. Uptake of the labeled vitamin B₁₂ in human marrow is largely by the granulocyte series and is greater in marrows from vitamin B₁₂-deficient individuals than from normal subjects.     

VEGETARIAN DIET AND VITAMIN B12 DEFICIENCY

Many people ingesting low levels of vitamin B₁₂ for many years appear to achieve a balance that does not lead to overt signs and symptoms of deficiency. The development of neurologic abnormalities due to vitamin B₁₂ deficiency on a strict vegetarian diet of 25 years was apparently related to an associated subtle malabsorption of vitamin B₁₂.     

VITAMIN B12 ANALOGUES AND INTESTINAL BACTERIA

Bacterial production of analogues of vitamin B₁₂, by small-bowel bacteria results in significant loss of vitamin B₁₂ to the host. Bacterial production of cobamides occurs de novo as well as from vitamin B₁₂ bound to intrinsic factor.     

Nutrient density and variation in nutrient intake with changing energy intake in multimorbid nursing home residents

Background:  The low energy intake seen in some institutionalised elderly has led to a focus on energy dense diets. The present study aimed to investigate nutrient density in the diet of nursing home residents, and calculate how changes in energy intake affect nutrient intake.
Methods:  The investigation comprised a longitudinal observational study analysing the relation between energy and nutrient intake in a general nursing home in Sweden. Food intake was weighed for 5 days every sixth month over 1.5 years and nutrient density was calculated. The 52 multimorbid residents [mean (range) age 84 (67–102) years] with three complete 5-day weighed food records were included in the study. A mixed linear model was used to calculate changes in nutrient intake with changing energy intake.
Results:  Nutrient density was adequate for vitamins A, B₁₂, thiamine, riboflavin and niacin, and low for vitamins D and E, folate, potassium, magnesium and iron. The mixed linear model showed that the fat-soluble vitamins, as well as folate and vitamin B₁₂, increased the most with increasing energy intake, whereas sodium, potassium, thiamine and selenium had the smallest increase.
Conclusions:  Nutritional density of the food should be considered when planning diets for elderly patients with poor appetite.     

Folate, Vitamin B12, and Neuropsychiatric Disorders

Folate and vitamin B₁₂ are required both in the methylation of homocysteine to methionine and in the synthesis of S-adenosylmethionine. S-ad-enosylmethionine is involved in numerous methylation reactions involving proteins, phospholipids, DNA, and neurotransmitter metabolism. Both folate and vitamin B₁₂ deficiency may cause similar neurologic and psychiatric disturbances including depression, dementia, and a demyelinating myelopathy. A current theory proposes that a defect in methylation processes is central to the biochemical basis of the neuropsychiatry of these vitamin deficiencies. Folate deficiency may specifically affect central monoamine metabolism and aggravate depressive disorders. In addition, the neurotoxic effects of homocysteine may also play a role in the neurologic and psychiatric disturbances that are associated with folate and vitamin B₁₂ deficiency.     

ROLE OF INTESTINAL MICROFLORA IN VITAMIN B6 METABOLISM

Similar metabolism of vitamin B₆ compounds has been observed in conventional and germfree rats and guinea pigs. These findings suggest that intestinal microorganisms contribute little to the vitamin B₆ nutriture of these animals when intake of the vitamin is adequate.     

VITAMIN B6 AND B12 RELATIONSHIPS

Feeding rats a diet deficient in Vitamin B₆ results in the lowering of vitamin B₁₂ reserve as manifested by a low B₁₂ serum level and subnormal hepatic storage.     

DIETARY PROTEIN AND VITAMIN B6 REQUIREMENTS

Dietary protein increases the vitamin B₆ requirement, but may also favor retention of the vitamin in the liver when intake of the vitamin is high.     

Oral Synthetic Folic Acid and Vitamin B12 Supplements Work—If One Consumes Them

Oral supplements of synthetic folic acid and vitamin B₁₂ are very effective in increasing blood levels of the vitamins and are known to prevent birth defects and cardiovascular diseases.     

Vitamin B12 Deficiency, Tumor Necrosis Factor-α and Epidermal Growth Factor: A Novel Function for Vitamin B12?

Vitamin B₁₂ deficiency was recently shown to be associated with elevated levels of tumor necrosis factor-α and decreased levels of epidermal growth factor in both rats and humans. These findings suggest a novel pathogenetic mechanism underlying the neuropathology of vitamin B₁₂ deficiency. They may also explain putative relationships between vitamin B₁₂ deficiency and certain disorders, including Alzheimer's disease, rheumatoid arthritis, and AIDS.     

ORIGIN AND FUNCTION OF HUMAN PLASMA R-TYPE VITAMIN B12 BINDING PROTEINS

Transcobalamin III (TC III) appears to be identical to granulocyte vitamin B₁₂-binding protein (GBP). In plasma it may be an artifact coming from granulocytes after the blood is collected. R-type B₁₂-binding proteins, particularly GBP, may provide a selective mechanism for removal of vitamin B₁₂ and analogues to the liver and elimination through bile.     

RARE FORMS OF FAMILIAL VITAMIN B12 MALABSORPTION IN CHILDREN

Because of the complexity of the vitamin B₁₂ absorption mechanism, there are many sites at which defects could occur. Sophisticated diagnostic techniques have led to identification of three unique B₁₂ absorptive defects, requiring different methods of treatment.     

VITAMIN B6 DEFICIENCY AND IMMUNE RESPONSES

The effect of vitamin B₆ deficiency on the immune response is briefly reviewed. The mechanisms involved in the immunosuppressive effect of vitamin B₆ deficiency are unclear.     

Effect of vitamin B12 deficiency on neurodevelopment in infants: current knowledge and possible mechanisms

Severe vitamin B₁₂ deficiency produces a cluster of neurological symptoms in infants, including irritability, failure to thrive, apathy, anorexia, and developmental regression, which respond remarkably rapidly to supplementation. The underlying mechanisms may involve delayed myelination or demyelination of nerves; alteration in the S-adenosylmethionine:S-adenosylhomocysteine ratio; imbalance of neurotrophic and neurotoxic cytokines; and/or accumulation of lactate in brain cells. This review summarizes the current knowledge concerning infantile vitamin B₁₂ deficiency, including a pooled analysis of case studies of infants born to mothers with untreated pernicious anemia or a strict vegetarian lifestyle and a discussion of the mechanisms that may underlie the manifestations of deficiency.     

Metabolic Changes Accompanying low Vitamin B6 Intakes

Changes occurring in college students on a low vitamin B₆ intake suggest that xanthurenic acid excretion after a tryplophan test dose, lymphocyte count and blood pyridoxine may indicate nutritional status for vitamin B₆.     

DIETARY FIBER AND VITAMIN B12 BALANCE

Inclusion of either cellulose or pectin in a fiber-free basal diet increased the rate of fecal excretion of vitamin B₁₂. In addition, pectin supplements stimulated a nine- to 21-fold increase in urinary excretion of methylmalonic acid.     

PITFALLS IN THE DIAGNOSIS OF VITAMIN B12 DEFICIENCY BY RADIODILUTION ASSAY

The inadequacies of radiodilution assays in the diagnosis of vitamin B₁₂ deficiency have been demonstrated. Inappropriately high levels of the vitamin may be recorded due to the use of relatively non-specific binders which detect inactive cobalamin analogues in plasma.     

ORAL CONTRACEPTIVES AND VITAMIN B6

Women taking oral contraceptives containing estrogen show an abnormality of tryptophan metabolism, and approximately one-fourth show clear evidence of vitamin B₆ deficiency.