Absorption of cyanocobalamin, coenzyme B 12 , methylcobalamin, and hydroxocobalamin at different dose levels

Vitamin B12-Multifaceted In Vivo Functions and In Vitro Applications

Vitamin B12 plays a key role in DNA stability. Research indicates that vitamin B12 deficiency leads to indirect DNA damage, and vitamin B12 supplementation may reverse this effect. Vitamin B12 acts as a cofactor for enzymes such as methionine synthase and methylmalonyl-CoA mutase, which are involved in DNA methylation and nucleotide synthesis. These processes are essential for DNA replication and transcription, and any impairment can result in genetic instability. In addition, vitamin B12 has antioxidant properties that help protect DNA from damage caused by reactive oxygen species. This protection is achieved by scavenging free radicals and reducing oxidative stress. In addition to their protective functions, cobalamins can also generate DNA-damaging radicals in vitro that can be useful in scientific research. Research is also being conducted on the use of vitamin B12 in medicine as vectors for xenobiotics. In summary, vitamin B12 is an essential micronutrient that plays a vital role in DNA stability. It acts as a cofactor for enzymes involved in the synthesis of nucleotides, has antioxidant properties and has potential value as a generator of DNA-damaging radicals and drug transporters.

Genetically predicted levels of folate, vitamin B12, and risk of autoimmune diseases: A Mendelian randomization study

Background

Evidence from observational studies on the association of folate and vitamin B12 with autoimmune diseases are conflicting.

Objective

We aimed to investigate the relationship of folate and vitamin B12 with autoimmune diseases using Mendelian randomization (MR).

Materials and methods

We selected single-nucleotide polymorphisms associated with folate and vitamin B12 at the genome-wide significance level. Summary-level data for four common autoimmune diseases (vitiligo, inflammatory bowel disease, rheumatoid arthritis, and systemic lupus erythematosus) were obtained from large-scale genome-wide association studies, with a sample size of 44,266, 86,640, 58,284, and 23,210, respectively. MR analyses were conducted using the inverse variance weighted (IVW) approach, and sensitivity analyses were further performed to test the robustness.

Results

We found that a higher genetically determined serum folate level per one standard deviation (SD) was associated with a decreased risk of vitiligo by the IVW method [odds ratios (OR) = 0.47; 95% confidence interval (CI): 0.32–0.69; P = 1.33 × 10-4]. Sensitivity analyses using alternative methods showed similar associations, and no evidence of pleiotropy was detected by MR-Egger regression (P = 0.919). In addition, we observed that vitamin B12 per one SD was positively associated with IBD (IVW: OR = 1.14, 95% CI: 1.03–1.26, P = 0.010; maximum likelihood: OR = 1.14, 95% CI: 1.01–1.29, P = 0.035; MR-PRESSO: OR = 1.14, 95% CI:1.01–1.28, P =0.037), while the association was not significant after Bonferroni correction.

Conclusion

The study provides convincing evidence for an inverse association between serum folate level and risk of vitiligo. Further studies are warranted to elucidate the possible association between vitamin B12 and risk of IBD.

Vitamin B12 Supplementation Adequacy in Australian Vegan Study Participants

In our initial analysis of the Australian Vegan Study we estimated the mean daily intake of vitamin B12 of each participant and compared this to the Recommended Dietary Intake (RDI). However, the proportion of vitamin B12 that can be absorbed from large doses typically contained in oral supplements is considerably lower than the amount absorbed from food. In this analysis we took into account the estimated absorption from supplements in order to compare adequacy of vitamin B12 intake to the RDI. A cross-sectional online survey was used to obtain information from women (N = 1530) of reproductive age on a vegan diet in Australia. Vitamin B12 intake from food was estimated using a validated food frequency questionnaire and detailed questioning was used to estimate supplemental intake. We used published data on dose-dependent absorption rates to estimate amount of the vitamin absorbed to enable comparison to the RDI. Supplementation practices varied widely. Based on estimated amount absorbed, 39% of participants had an estimated total intake of vitamin B12 below RDI equivalency, compared to 26% based on mean daily intake. The potential absorption of vitamin B12 needs to be considered when estimating adequacy of intake and recommending supplementation.

Vitamin B supplementation for sickle cell disease

This is a protocol for a Cochrane Review (intervention). The objectives are as follows:

To assess the effectiveness of vitamin B supplementation in children and adults with sickle cell disease (SCD), compared to no intervention or an alternative vitamin B supplementation given as part of standard care.

Vegan nutrition: a preliminary guide for health professionals

Since the beginning of the 21st century, interest in vegan diets has been rapidly increasing in most countries. Misconceptions about vegan diets are widespread among the general population and health professionals. Vegan diets can be health-promoting and may offer certain important advantages compared to typical Western (and other mainstream) eating patterns. However, adequate dietary sources/supplements of nutrients of focus specific to vegan diets should be identified and communicated. Without supplements/fortified foods, severe vitamin B12 deficiency may occur. Other potential nutrients of focus are calcium, vitamin D, iodine, omega-3 fatty acids, iron, zinc, selenium, vitamin A, and protein. Ensuring adequate nutrient status is particularly important during pregnancy, lactation, infancy, and childhood. Health professionals are often expected to be able to provide advice on the topic of vegan nutrition, but a precise and practical vegan nutrition guide for health professionals is lacking. Consequently, it is important and urgent to provide such a set of dietary recommendations. It is the aim of this article to provide vegan nutrition guidelines, based on current evidence, which can easily be communicated to vegan patients/clients, with the goal of ensuring adequate nutrient status in vegans.

Efficiency of the sublingual route in treating B12 deficiency in infants

Objective: To evaluate the efficiency of the sublingual route for the treatment of vitamin B12 deficiency in infants. Background: Vitamin B12 deficiency is common in children. In breastfed infants, the main reason is maternal B12 deficiency. Parenteral administration is commonly prescribed. However, patient compliance is not satisfactory due to repeated painful parenteral applications. It is also known that the oral route is efficient in high doses. In recent years, the sublingual route has been tried. This route stands out due to its easy applicability and low cost. However, there are few efficacy studies in infants for the sublingual route. Materials and methods: The study included 49 infants aged 6-12 months. All infants with marginal or deficient B12 levels (<300 pg/mL) were incidentally detected and treated with sublingual methylcobalamin. Each dose was 1000 μg and administered once a day in the first week, every other day in the second week, twice a week in the third week, and once a week in the last week. Serum vitamin B12 levels were measured before and after the treatment. Paired Sample T-Test was used to compare variables. Results: All infants had normal physical development and had no hematological or neurological issues. It was learned from the parents that the infants tolerated treatment well, and no side effects related to the treatment, such as vomiting or rash, were observed. Before and after the treatment, the mean vitamin B12 levels were 199±57 pg/mL and 684±336 pg/ml, respectively. The difference between the means was statistically significant (p<0.001). Conclusion: According to the study, it seems possible to treat vitamin B12 deficiency via a sublingual route in infants. In addition, methylcobalamin can be an alternative to the commonly used cyanocobalamin.

Efficacy of supplementation with methylcobalamin and cyancobalamin in maintaining the level of serum holotranscobalamin in a group of plant-based diet (vegan) adults

Plant-based nutrition has become extremely popular in the contemporary era. Its positive effects are sustained by many studies, but one of its risks is that it is almost completely devoid of vitamin B12. In the present study, we analyzed the effects of two types of vitamin B12 supplements, cyancobalamin and methylcobalamin on the level of active serum vitamin (holotranscobalamin) in a group of Romanian individuals (n=42) following a (vegan) plant-based diet. The results revealed that cyancobalamin gives better results in maintaining B12, as quantified by the holotranscobalamin value (median=150 pcg/l) when compared with methylcobalamin (median=78.5 pcg/l). The frequency of administration, regardless of the quantity in one dose, is another important factor in maintaining the holotranscobalamin level within suitable limits. More frequent intakes give more optimal results. Vegans trying to supplement with alternative products (algae, kombucha, other fermented products), had the lowest levels of holotranscobalamin, always bellow the recommended level of 35 pcg/l (median=29 pcg/l). Vegans must be educated on B12 supplementation, about the pharmaceutical forms on the market and their performances and on choosing the optimal plan in order to avoid the onset of B12 deficiency.

Vitamin B12 status in health and disease: a critical review. Diagnosis of deficiency and insufficiency - clinical and laboratory pitfalls

Vitamin B₁₂ (cobalamin) is an essential cofactor for two metabolic pathways. It is obtained principally from food of animal origin. Cobalamin becomes bioavailable through a series of steps pertaining to its release from dietary protein, intrinsic factor-mediated absorption, haptocorrin or transcobalamin-mediated transport, cellular uptake, and two enzymatic conversions (via methionine synthase and methylmalonyl-CoA-mutase) into cofactor forms: methylcobalamin and adenosylcobalamin. Vitamin B₁₂ deficiency can masquerade as a multitude of illnesses, presenting different perspectives from the point of view of the hematologist, neurologist, gastroenterologist, general physician, or dietician. Increased physician vigilance and heightened patient awareness often account for its early presentation, and testing sometimes occurs during a phase of vitamin B₁₂ insufficiency before the main onset of the disease. The chosen test often depends on its availability rather than on the diagnostic performance and sensitivity to irrelevant factors interfering with vitamin B₁₂ markers. Although serum B₁₂ is still the most commonly used and widely available test, diagnostics by holotranscobalamin, serum methylmalonic acid, and plasma homocysteine measurements have grown in the last several years in routine practice. The lack of a robust absorption test, coupled with compromised sensitivity and specificity of other tests (intrinsic factor and gastric parietal cell antibodies), hinders determination of the cause for depleted B₁₂ status. This can lead to incorrect supplementation regimes and uncertainty regarding later treatment. This review discusses currently available knowledge on vitamin B₁₂, informs the reader about the pitfalls of tests for assessing its deficiency, reviews B₁₂ status in various populations at different disease stages, and provides recommendations for interpretation, treatment, and associated risks. Future directions for diagnostics of B₁₂ status and health interventions are also discussed.

Intake of vitamin B12 and other characteristics of women of reproductive age on a vegan diet in Australia

OBJECTIVE

(i) To examine demographic and health characteristics of women of reproductive age on a vegan diet in Australia and compare these to the general population; (ii) to identify sources and intake of vitamin B12 and compare intake to current recommendations and (iii) examine associations between participant characteristics and adequacy of vitamin B12 intake.

DESIGN

In this cross-sectional study, data were collected via an online survey. Demographic and health characteristics of women on a vegan diet were compared with women in the general population (using Australian Bureau of Statistics data). Intake of vitamin B12 was estimated using a FFQ and estimation of supplemental intake.

SETTING

Australia.

PARTICIPANTS

Participants (n 1530) were women aged 18-44 years who had been on a vegan diet for at least 6 months.

RESULTS

While BMI, smoking habits and intakes of fruit and vegetables compared favourably with the general population, 26 % of respondents had estimated intakes of vitamin B12 below recommendations. Analyses of relationships between vitamin B12 intake and participant characteristics revealed that the strongest predictor of intake was supplementation (P < 0·001); however, 25 % had not supplemented with vitamin B12 in the past 3 months.

CONCLUSIONS

The vitamin B12 intakes of a substantial proportion of Australian women of reproductive age consuming a vegan diet do not meet the recommended intake, which could adversely affect their health, and, if they are pregnant or lactating, that of their infants too. There is a need for further research in this area to identify effective strategies to address this situation.

Measuring vitamin B-12 bioavailability with [13C]-cyanocobalamin in humans

BACKGROUND

Vitamin B-12 deficiency is widespread in many parts of the world, affecting all age groups and increasing with age. It is primarily due to a low intake of animal source foods or malabsorption. The measurement of bioavailability of vitamin B-12 is etiologically important in deficiency but is limited due to the use of radioactive isotopes like [57Co]- or [14C]-cyanocobalamin.

OBJECTIVES

The aim of this study was to measure the bioavailability of [13C]-cyanocobalamin in humans and to assess the effect of parenteral replenishment of vitamin B-12 on the bioavailability.

METHODS

We synthesized a stable isotope-labeled vitamin B-12, [13C]-cyanocobalamin, using Salmonella enterica by providing [13C2]-ethanolamine as a sole carbon source. After purification and mass spectrometry-based characterization, its oral bioavailability was measured in the fasted state with high and low oral doses, before and after parenteral replenishment of vitamin B-12 stores, from the kinetics of its plasma appearance in a 2-compartment model.

RESULTS

[13C]-cyanocobalamin was completely decyanated to [13C]-methylcobalamin describing metabolic utilization, and its plasma appearance showed early and late absorption phases. At a low dose of 2.3 µg, the mean bioavailability was 46.2 ± 12.8 (%, mean ± SD, n = 11). At a higher dose of 18.3 µg, the mean bioavailability was 7.6 ± 1.7 (%, mean ± SD, n = 4). Parenteral replenishment of the vitamin B-12 store in deficient individuals prior to the measurement resulted in a 1.9-fold increase in bioavailability.

CONCLUSIONS

Vitamin B-12 bioavailability is dose dependent and at a low dose that approximates the normal daily requirement (46%). The stable isotope method described here could be used to define the etiology of deficiency and to inform the dietary requirement in different physiologic states as well as the dose required for supplementation and food fortification. This trial was registered at the Clinical Trials Registry of India as CTRI/2018/04/012957.

The tissue profile of metabolically active coenzyme forms of vitamin B12 differs in vitamin B12-depleted rats treated with hydroxo-B12 or cyano-B12

Recent rat studies show different tissue distributions of vitamin B12 (B12), administered orally as hydroxo-B12 (HO-B12) (predominant in food) and cyano-B12 (CN-B12) (common in supplements). Here we examine male Wistar rats kept on a low-B12 diet for 4 weeks followed by a 2-week period on diets with HO-B12 (n 9) or CN-B12 (n 9), or maintained on a low-B12 diet (n 9). Plasma B12 was analysed before, during and after the study. The content of B12 and its variants (HO-B12, glutathionyl-B12, CN-B12, 5'-deoxyadenosyl-B12 (ADO-B12), and methyl-B12 (CH3-B12)) were assessed in the tissues at the end of the study. A period of 4 weeks on the low-B12 diet reduced plasma B12 by 58 % (from median 1323 (range 602-1791) to 562 (range 267-865) pmol/l, n 27). After 2 weeks on a high-B12 diet (week 6 v. week 4), plasma B12 increased by 68 % (HO-B12) and 131 % (CN-B12). Total B12 in the tissues accumulated differently: HO-B12>CN-B12 (liver, spleen), HO-B12<CN-B12 (kidneys), and HO-B12≈CN-B12 (brain, heart). Notably, more than half of the administered CN-B12 remained in this form in the kidneys, whereas HO-B12 was largely converted to the bioactive ADO-B12. Only <10 % of the other cofactor, CH3-B12, were found in the tissues. In conclusion, dietary CN-B12 caused a higher increase in plasma and total kidney B12 but provided less than half of the active coenzymes in comparison to dietary HO-B12. These data argue that HO-B12 may provide a better tissue supply of B12 than CN-B12, thereby underscoring the lack of a direct relation between plasma B12 and tissue B12.

Comparative Bioavailability of Synthetic B12 and Dietary Vitamin B12 Present in Cow and Buffalo Milk: A Prospective Study in Lactovegetarian Indians

We assessed improvements in the vitamin B12 status of Indian lactovegetarians receiving four weeks supplementation with natural B12 in milk versus cyano-B12 in capsules. Three groups (n = 22, 23, 22) received daily oral doses of cyano-B12 (2 × 0.76 µg) or milk (2 × 200 mL) from a cow or buffalo (amounting to B12 ≈ 2 × 0.76 µg). Their blood was examined at baseline and each following week. The baselines (median (min/max)) indicated a low B12 status: plasma B12 (116(51/314)) pmol/L, holotranscobalamin (holoTC) (30(7/119)) pmol/L, total homocysteine (Hcy) (24(10/118)) µmol/L, methylmalonic acid (MMA) (0.58(0.15/2.2)) µmol/L and combined B12 index (cB12) (-1.32 - (-3.12/+0.29)). Shifts from the baselines (B12, holoTC, cB12) and ratios to the baselines (Hcy, MMA) were analyzed over time. The cyano-B12 treatment gave more total B12 in plasma at week one (+29 pmol/L, p = 0.004) but showed no further increase. Other biomarkers changed more comparably between the three groups (p ≥ 0.05): holoTC showed a transient spike that leveled off, Hcy finally decreased to 0.8 × baseline, while MMA showed marginal changes. The combined indexes improved comparably (p = 0.6) in all groups (+0.2(-0.3/+0.9), p ≤ 0.002). In conclusion, the tested formulations similarly improved B12 status, but did not normalize it.

Differences in Tissue Distribution of Cyano⁻B12 and Hydroxo⁻B12 One Week after Oral Intake: An Experimental Study in Male Wistar Rats

Foods contain natural vitamin B12 forms, such as hydroxo–B12 (HO–B12), whereas vitamin pills contain the synthetic cyano–B12 (CN–B12). Recent studies in rats showed different tissue distributions of CN–B12 and HO–B12 24 h after oral administration. Here, we investigate whether these differences are sustained or leveled out with time in both B12-deplete and -replete rats, thereby assessing if the two forms are equally good at maintaining a normal B12 status. Male Wistar rats were fed diets with low (n = 16) or high (n = 12) B12 content for 17 days. At day 10, the rats received a single oral dose of [⁵⁷Co]-labeled CN–B12 or HO–B12 (n = 6 and n = 8, respectively, in each diet group). The rats were sacrificed on day 17 and endogenous B12 and [⁵⁷Co]–B12 were measured in liver, kidney, and plasma. We found that the low-B12 diet introduced a B12-deplete state as judged from medians of endogenous B12 compared to rats on a (high-B12 diet): Plasma (565 (1410) pmol/L), liver (28.2 (33.2) pmol/g), and kidneys (123 (1300) pmol/g). One week after oral administration, the labeled B12 was distributed as follows: HO–B12 > CN–B12 (liver) and CN–B12 > HO–B12 (kidneys, plasma). The tissue/plasma ratios showed different equilibriums for labeled CN–B12 and HO–B12 in the B12-deplete and -replete groups. The equilibrium of endogenous B12 resembled [⁵⁷Co]CN–B12 in replete rats but differed from both [⁵⁷Co]CN–B12 and [⁵⁷Co]HO–B12 in deplete rats. The data suggest long-term differences in tissue utilization of the two B12 forms and warrant further studies concerning the possible benefits of consuming HO–B12 instead of CN–B12 in oral B12 replacement.

Bioavailability of Vitamin B12 from Dairy Products Using a Pig Model

The present study compares the bioavailability of vitamin B₁₂ (B₁₂) of dairy products or synthetic B₁₂, using the pig as an experimental model for humans. Eleven pigs were used in a cross-over design to assess the net portal drained viscera (PDV) flux of blood plasma B₁₂ after ingestion of tofu (TF; devoid of B₁₂), Swiss cheese (SC), Cheddar cheese (CC), yogurt (YG), and synthetic B₁₂ (TB₁₂; TF supplemented with cyanocobalamin), providing a total of 25 µg of B₁₂ each. PDV blood plasma flow for SC and CC were higher than for TF and TB₁₂ (p ≤ 0.04) whereas YG was higher than TF (p = 0.05). Porto-arterial difference of blood plasma B₁₂ concentrations were higher for CC and TB₁₂ than for TF and YG (p ≤ 0.04) but not different from SC (p ≥ 0.15). Net PDV flux of B₁₂ was only different from zero for CC. However, the net PDV flux of B₁₂ for CC was not different from SC or TB₁₂. Cumulative net PDV flux of B₁₂ for SC, TB₁₂, and CC were 2.9, 4.4, and 8.3 µg 23 h post-meal, corresponding to a bioavailability of 11.6%, 17.5%, and 33.0%, respectively. In conclusion, CC had the best bioavailability of B₁₂ among the tested dairy products or compared to synthetic B₁₂.

Dietary Intake of Vitamin B12 is Better for Restoring a Low B12 Status Than a Daily High-Dose Vitamin Pill: An Experimental Study in Rats

Vitamin B12 (B12) is present in foods of animal origin, and vegans are encouraged to take supplements with synthetic B12 in order to ensure a sufficient uptake. Recent rat studies suggest that natural (hydroxo-B12, HO-B12) and synthetic (cyano-B12, CN-B12) B12 behave differently in the body. Here, we test if a daily vitamin pill matches dietary B12 in ability to restore a low B12 status in rats. B12-depleted male Wistar rats (n = 60) were divided into five groups (n = 12 in each) and subjected to two weeks intervention with various schemes of B12 supplementation. Two “dietary” groups received a low-B12 chow that was fortified with either HO-B12 or CN-B12 providing a continuous supply. Two “pill” groups received a single daily dose of CN-B12, where the vitamin content either matched or exceeded by factor four the provisions for the “dietary” groups. A control group received the low-B12 chow without B12 fortification. B12 was measured in plasma and tissues. Dietary B12 provides 35% more B12 to the tissues than an equivalent single daily dose (p < 0.0001). Natural B12 delivers 25% more B12 to the liver than synthetic B12 (p = 0.0007). A fourfold increase in B12, supplemented as a single daily dose, does not provide any extra B12 to the tissues (p = 0.45). We conclude that dietary B12 is better at rescuing a low B12 status than a daily vitamin pill.

Effect of 8-week oral supplementation with 3-µg cyano-B12 or hydroxo-B12 in a vitamin B12-deficient population

PURPOSE

We compare the effect of 8-week oral supplementation with cyano-B12 (currently used in vitamin pills) and hydroxo-B12 (predominant form in the diet) in a population with nutritional vitamin B12 deficiency.

METHODS

Fifty-one healthy Indian adults with baseline serum cobalamin < 200 pmol/L were supplied for 8 weeks with daily oral supplements of 3-µg cyano-B12 (n = 15), 3-µg hydroxo-B12 (n = 16), or a placebo (n = 20). Blood at baseline, and each following week, was examined for total cobalamin, holotranscobalamin, methylmalonic acid, and homocysteine.

RESULTS

The study groups did not differ at baseline and were characterized by [median (range)] serum cobalamin [128 (68-191) pmol/L], holotranscobalamin [16 (6-41) pmol/L], methylmalonic acid [0.8 (0.3-1.7) µmol/L], homocysteine [17.9 (8.5-100.9) µmol/L], and a combined indicator of B12 status 4cB12 of - 1.65 (- 0.64 to - 4.07). The group supplemented with cyano-B12 showed a higher increase in total serum cobalamin than the group treated with hydroxo-B12, while other biomarkers changed comparably in the two groups. After 8 weeks of treatment, the biomarker values of the supplemented groups (pooled) differed significantly from the placebo group. Yet, the vitamin B12 status was still poor [cobalamin: 168 (87-302) pmol/L; holotranscobalamin: 19 (8-45) pmol/L; methylmalonic acid: 0.7 (0.2-1.7) µmol/L; homocysteine: 17.2 (2.6-96.8) µmol/L; 4cB12 = - 1.34 (- 0.33 to - 3.3)].

CONCLUSION

8-week supplementation with 3-µg cyano-B12 elevated serum cobalamin more than 3 µg hydroxo-B12, but all other biomarkers changed similarly in both groups. Supplementation with 3 µg vitamin B12 did not reverse the low status in individuals with nutritional vitamin B12 deficiency.

CLINICAL TRIAL REGISTRY OF INDIA

REF/2017/02/013343.

Increase in circulating holotranscobalamin after oral administration of cyanocobalamin or hydroxocobalamin in healthy adults with low and normal cobalamin status

Purpose

To investigate the absorption of synthetic cyanocobalamin and natural occurring hydroxocobalamin in populations with low and normal cobalamin (vitamin B12) status.

Methods

We included adults with low (n = 59) and normal (n = 42) cobalamin status and measured the change in serum holotranscobalamin (ΔholoTC) before and after 2 day administration of different doses of cyanocobalamin and hydroxocobalamin (CobaSorb test). In the low status group, the test was performed using a cross-over design with identical doses of both cobalamin forms (1.5, 3, and 6 µg, respectively). In the normal status group, the test was performed with either 3, 6, and 9 µg cyanocobalamin (n = 28), or with 9 µg cyanocobalamin and 9 µg hydroxocobalamin (n = 14).

Results

In both groups, median ΔholoTC (pmol/L) was higher after intake of cyanocobalamin compared to (hydroxocobalamin) [low status: 1.5 µg: 19 (6); 3 µg: 23 (7); 6 µg: 30 (14); normal status: 9 µg: 30 (13) pmol/L]. Independent of B12 form, no difference was observed in ΔholoTC between those receiving 1.5 and 3 µg in the low status group or 6 and 9 µg cyanocobalamin in the normal status group. However, in both groups, administration of 6 µg cobalamin resulted in a significant higher ΔholoTC than did 3 µg [low status: p = 0.02 (0.009) for cyanocobalamin (hydroxocobalamin); normal status: p = 0.03 for cyanocobalamin].

Conclusions

Administration of cyanocobalamin resulted in a more than twofold increase in holoTC in comparison with hydroxocobalamin. The absorptive capacity was reached only by doses above 3 µg cobalamin. Our results underscore the importance of using the same form of cobalamin when comparing uptake under different conditions.

Clinical trial registry number

NCT02832726 at https://clinicaltrials.gov and 2016/09/012147 at Clinical Trials Registry India.

Electronic supplementary material

The online version of this article (doi:10.1007/s00394-017-1553-5) contains supplementary material, which is available to authorized users.

Tissue distribution of oral vitamin B12 is influenced by B12 status and B12 form: an experimental study in rats

Purpose

Hydroxocobalamin (HOCbl) is the dominating Cbl form in food, whereas cyanocobalamin (CNCbl) is common in vitamin pills and oral supplements. This study compares single-dose absorption and distribution of oral HO[⁵⁷Co]Cbl and CN[⁵⁷Co]Cbl in Cbl-deficient and normal rats.

Methods

Male Wistar rats (7 weeks) were fed a 14-day diet with (n = 15) or without (n = 15) Cbl. We compared the uptakes of HO[⁵⁷Co]Cbl (free or bound to bovine transcobalamin) and free CN[⁵⁷Co]Cbl administered by gastric gavage (n = 5 in each diet group). Rats were sacrificed after 24 h. Blood, liver, kidney, brain, heart, spleen, intestines, skeletal muscle, 24-h urine and faeces were collected, and the content of [⁵⁷Co]Cbl was measured. Endogenous Cbl in tissues and plasma was analysed by routine methods.

Results

Mean endogenous plasma-Cbl was sevenfold lower in deficient vs. normal rats (190 vs. 1330 pmol/L, p < 0.0001). Cbl depletion increased endogenous Cbl ratios (tissue/plasma = k_in/k_out) in all organs except for the kidney, where the ratio decreased considerably. Twenty-four-hour accumulation of labelled Cbl showed that HOCbl > CNCbl (liver) and CNCbl > HOCbl (brain, muscle and plasma).

Conclusions

The Cbl status of rats and the administered Cbl form influence 24-h Cbl accumulation in tissues and plasma.

Electronic supplementary material

The online version of this article (doi:10.1007/s00394-017-1424-0) contains supplementary material, which is available to authorized users.

Vitamin B12 among Vegetarians: Status, Assessment and Supplementation

Cobalamin is an essential molecule for humans. It acts as a cofactor in one-carbon transfers through methylation and molecular rearrangement. These functions take place in fatty acid, amino acid and nucleic acid metabolic pathways. The deficiency of vitamin B12 is clinically manifested in the blood and nervous system where the cobalamin plays a key role in cell replication and in fatty acid metabolism. Hypovitaminosis arises from inadequate absorption, from genetic defects that alter transport through the body, or from inadequate intake as a result of diet. With the growing adoption of vegetarian eating styles in Western countries, there is growing focus on whether diets that exclude animal foods are adequate. Since food availability in these countries is not a problem, and therefore plant foods are sufficiently adequate, the most delicate issue remains the contribution of cobalamin, which is poorly represented in plants. In this review, we will discuss the status of vitamin B12 among vegetarians, the diagnostic markers for the detection of cobalamin deficiency and appropriate sources for sufficient intake, through the description of the features and functions of vitamin B12 and its absorption mechanism.

Cobalamin coenzyme forms are not likely to be superior to cyano- and hydroxyl-cobalamin in prevention or treatment of cobalamin deficiency

Methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl) are coenzymes for methionine synthase and methylmalonyl-CoA mutase, respectively. Hydroxylcobalamin (HOCbl) and cyanocobalamin (CNCbl) are frequently used for supplementation. MeCbl and AdoCbl have recently emerged as alternative forms in supplements. In the light of metabolic transformation of Cbl into its cofactor forms, this review discusses current evidence on efficacy and utility of different Cbl forms in preventing or treating Cbl deficiency. Cbl-transporting proteins bind and mediate the uptake of all aforementioned forms of Cbl. After internalization and lysosomal release, Cbl binds to the cytosolic chaperon MMACHC that is responsible for (i) flavin-dependent decyanation of [CN-Co³⁺]Cbl to [Co²⁺]Cbl; (ii) glutathione-dependent dealkylation of MeCbl and AdoCbl to [Co^2+/1+]Cbl; and (iii) glutathione-dependent decyanation of CNCbl or reduction of HOCbl under anaerobic conditions. MMACHC shows a broad specificity for Cbl forms and supplies the Cbl²⁺ intermediate for synthesis of MeCbl and AdoCbl. Cobalamin chemistry, physiology, and biochemistry suggest that MeCbl and AdoCbl follow the same route of intracellular processing as CNCbl does. We conclude that supplementing MeCbl or AdoCbl is unlikely to be advantageous compared to CNCbl. On the other hand, there are obvious advantages of high parenteral doses (1–2 mg) of HOCbl in treating inborn errors of Cbl metabolism.

High-dose compared with low-dose vitamin B-12 supplement use is not associated with higher vitamin B-12 status in children, adolescents, and older adults

Over-the-counter vitamin supplements on the Canadian market are permitted to contain a daily vitamin B-12 dose of up to 1000 μg. Our objective was to determine the association between total daily vitamin B-12 supplement dose and markers of vitamin B-12 status in Canadians. Blood collected from a nationally representative sample aged 6-79 y (n = ∼5600) in the Canadian Health Measures Survey (2007-2009) was analyzed for serum vitamin B-12 and plasma total homocysteine (tHcy). Total daily intake of vitamin B-12 from single and multivitamin supplements was calculated. Individuals that indicated proton pump inhibitor or vitamin B-12 injection treatment were excluded from the supplement dose and tHcy analyses; folate-deficient individuals were also excluded from the tHcy analysis. Twenty-three percent of children, 12.3% of adolescents, and 25.5% of adults consumed a vitamin B-12-containing supplement. Supplement users had 33% higher serum vitamin B-12 and 4.2% higher prevalence of adequacy than did non-supplement users. Children and adolescents consuming >10 μg/d supplemental vitamin B-12 did not demonstrate higher serum vitamin B-12, higher prevalence of serum vitamin B-12 adequacy, or lower tHcy than did those consuming >0-10 μg/d. The association between serum vitamin B-12 reached a plateau at doses of >25 and >10-25 μg/d in adults aged 46-59 and 60-79 y, respectively. The prevalences of serum vitamin B-12 adequacy and normal tHcy, and tHcy did not differ by vitamin B-12 supplement dose in adults >45 y. In this cross-sectional study, vitamin B-12 supplement doses >10-25 μg/d were not associated with higher vitamin B-12 status in children, adolescents, or older adults compared with lower doses.

Interventions with vitamins B6, B12 and C in pregnancy

The water-soluble vitamins B6, B12 and C play important roles in maternal health as well as fetal development and physiology during gestation. This systematic review evaluates the risks and benefits of interventions with vitamins B6, B12 and C during pregnancy on maternal, neonatal and child health and nutrition outcomes. Relevant publications were identified by searching PubMed, Popline and Web of Science databases. Meta-analyses were conducted for outcomes where results from at least three controlled trials were available. Potential benefits of vitamin B6 supplementation were reduction in nausea and vomiting, improvement in dental health, and treatment of some cases of anaemia. In meta-analysis based on three small studies, vitamin B6 supplementation had a significant positive effect on birthweight (d = 217 g [95% confidence interval (CI) 130, 304]). Interventions with vitamin C alone or combined with vitamin E did not systematically reduce the incidence of pre-eclampsia, premature rupture of membranes, or other adverse pregnancy outcomes. In meta-analyses, vitamins C and E increased the risk of pregnancy-related hypertension (relative risk 1.10 [95% CI 1.02, 1.19]). Effects of vitamin B6 or C intervention on other neonatal outcomes, including preterm birth, low birthweight, and perinatal morbidity and mortality, were not significant. Data on child health outcomes were lacking. Despite the prevalence of vitamin B12 deficiency amongst populations with limited intake of animal source foods, no intervention trials have evaluated vitamin B12 supplementation before or during pregnancy. In conclusion, existing evidence does not justify vitamin C supplementation during pregnancy. Additional studies are needed to confirm positive effects of vitamin B6 supplementation on infant birthweight and other outcomes. While vitamin B12 supplementation may reduce the incidence of neural tube defects in the offspring based on theoretical considerations, research is needed to support this hypothesis.

Bioavailability of vitamin B₁₂ in cows' milk

The natural source of vitamin B₁₂ in human diets comes from animal products. For example, one glass (250 ml) of milk provides approximately 50 % of the RDA (2·4 μg/d). It was hypothesised that the provision of vitamin B₁₂ from milk is more efficiently absorbed than the synthetic form used in vitamin supplements. Pigs (n 10) were used as a model for intestinal absorption of vitamin B₁₂ in humans to compare the net fluxes of vitamin B₁₂ across the portal-drained viscera (PDV; an indicator of intestinal absorption) after ingestion of meals complemented with conventional and vitamin B₁₂-enriched (via injections to cows) milk (raw, pasteurised or microfiltrated) or with equivalent amounts of cyanocobalamin, the synthetic form used in supplements or unsupplemented. Net flux of vitamin B₁₂ across PDV after the ingestion of milk was positive, though not influenced by milk enrichment (P>0·3) or technological processes (P = 0·8) and was greater than after ingestion of equivalent amounts of cyanocobalamin (cyanocobalamin v. all milk, P ≤ 0·003). In fact, net fluxes of this vitamin were not different from 0 after either cyanocobalamin or the meal devoid of vitamin B₁₂ (unsupplemented v. cyanocobalamin, P = 0·7). The cumulative PDV fluxes during the 24 h following ingestion of meals complemented with milk varied from 5·5 to 6·8 μg. These values correspond to an efficiency of intestinal absorption of vitamin B₁₂ from milk varying between 8 and 10 %. Therefore, vitamin B₁₂, which is abundant in cows' milk, is also substantially more available than the most commonly used synthetic form of this vitamin.

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.

Traveling the vitamin B12 pathway: oral delivery of protein and peptide drugs

Oral routes of administration for therapeutic peptides and proteins face two major barriers: proteolytic degradation in the stomach and an inadequate absorption mechanism for polypeptides within the intestinal lumen. As a result, peptide-based therapeutics are administered by injection, a painful process associated with lower patient compliance. The development of a means of overcoming these two major obstacles and enabling the successful delivery of peptide therapeutics by the oral route of administration has therefore been the target of extensive scientific endeavor. This Minireview focuses on oral peptide/protein delivery by the dietary uptake pathway for vitamin B(12). Recent progress in this field includes the delivery of erythropoietin, granulocyte-colony-stimulating factor, luteinizing-hormone-releasing hormone, and insulin.

Efficacy and safety of fortification and supplementation with vitamin B12: biochemical and physiological effects

Long known as an uncommon but serious medical disorder requiring medical management, vitamin B12 deficiency is now seen to be common worldwide, but it is in a quite different form than traditionally envisioned. Most of the newly recognized deficiency is subclinical in nature, its health impact and natural history are uncertain, and its prevalence has been greatly inflated by also including persons with "low-normal" vitamin B12 levels, few of whom are deficient. The spread of folic acid fortification has also introduced concerns about folate's potentially adverse neurologic consequences in persons with undetected vitamin B12 deficiency. Fortification with vitamin B12 may prove more complicated than fortification with folic acid, however, because the bioavailability of vitamin B12 is limited. Bioavailability for those who need the vitamin B12 the most is especially poor, because they often have malabsorption affecting either classical intrinsic factor-mediated absorption or food-vitamin B12 absorption. Moreover, new evidence shows that many elderly persons respond poorly to daily oral doses under 500 microg (1 microg = 0.74 nmol), even if they do not have classical malabsorption, which suggests that proposed fortification with 1 to 10 microg may be ineffective. Those least in need of vitamin B12 usually have normal absorption and are thus at greatest risk for whatever unknown adverse effects of high-dose fortification might emerge, such as the effects of excess accumulation of cyanocobalamin. Studies are needed to define the still unproven health benefits of vitamin B12 fortification, the optimal levels of fortification, the stability of such fortification, interactions with other nutrients, and any possible adverse effects on healthy persons. The answers will permit formulation of appropriately informed decisions about mandatory fortification or (because fortification may prove a poor choice) about targeted supplementation in subpopulations with special needs for additional vitamin B12, such as vegetarians, nursing mothers, and the elderly.

Causes of Vitamin B12 and Folate Deficiency

This review describes current knowledge of the main causes of vitamin B12 and folate deficiency. The most common explanations for poor vitamin B12 status are a low dietary intake of the vitamin (i.e., a low intake of animal-source foods) and malabsorption. Although it has long been known that strict vegetarians (vegans) are at risk for vitamin B12 deficiency, evidence now indicates that low intakes of animal-source foods, such as occur in some lacto-ovo vegetarians and many less-industrialized countries, cause vitamin B12 depletion. Malabsorption of the vitamin is most commonly observed as food-bound cobalamin malabsorption due to gastric atrophy in the elderly, and probably as a result of Helicobacter pylori infection. There is growing evidence that gene polymorphisms in transcobalamins affect plasma vitamin B12 concentrations. The primary cause of folate deficiency is low intake of sources rich in the vitamin, such as legumes and green leafy vegetables, and the consumption of these foods may explain why folate status can be adequate in relatively poor populations. Other situations in which the risk of folate deficiency increases include lactation and alcoholism.

National nutrition and public health policies: issues related to bioavailability of nutrients when developing dietary reference intakes

Dietary reference intakes (DRI), like its predecessor, the recommended dietary allowances (RDA) and the Recommended Nutrient Intakes (RNIs), are reference values, based on the best scientific evidence available. They serve as reference amounts of specific nutrients and food components for use in assessing the adequacy of and in planning for nutritious diets. They have been used for over 50 y as the basis for national nutrition monitoring and intervention programs in the United States, Canada, and other countries and as the basis for dietary guidance developed for both individuals and for targeted groups of people. Thus, although not developed for specific policy applications, they have represented the best scientific perspectives regarding what should be the basis for nutrition and public health policy related to foods and supplements. In determining DRIs, as was the case with the RDA, significant attention must be paid to the form of the nutrient or food component that is evaluated. Research conducted to determine how much of a nutrient is needed must evaluate the chemical form provided, the matrix in which it is given and the effect of other food components on absorption and/or utilization. Because the DRI recommendations will be used in population-wide policy development, assumptions must be made explicitly about what is expected for all of these factors in a typical diet. At the same time, where data exist relative to nontypical but potentially very significant effects on bioavailability, these must also be delineated to be of use in a variety of settings. Finally, one of the most important aspects of determining bioavailability in developing reference intakes is that as new information emerges, new complexities enter into the process. As more chemical complexes of nutrients and food components become available in the marketplace, new bioavailability factors may need to be established. Examples of such changes exist in the DRI reports already published for vitamin B-12 and folate and in previous RDA for iron and protein. It is often the different assumptions related to bioavailability that alter the reference intakes used as the basis for public health policy in different countries, rather than the basic science from which the recommendation is derived.

Vitamin B12 deficiency in the elderly

Vitamin B12 deficiency is estimated to affect 10%-15% of people over the age of 60, and the laboratory diagnosis is usually based on low serum vitamin B12 levels or elevated serum methylmalonic acid and homocysteine levels. Although elderly people with low vitamin B12 status frequently lack the classical signs and symptoms of vitamin B12 deficiency, e.g. megaloblastic anemia, precise evaluation and treatment in this population is important. Absorption of crystalline vitamin B12 does not decline with advancing age. However, compared with the younger population, absorption of protein-bound vitamin B12 is decreased in the elderly, owing to a high prevalence of atrophic gastritis in this age group. Atrophic gastritis results in a low acid-pepsin secretion by the gastric mucosa, which in turn results in a reduced release of free vitamin B12 from food proteins. Furthermore, hypochlorhydria in atrophic gastritis results in bacterial overgrowth of the stomach and small intestine, and these bacteria may bind vitamin B12 for their own use. The ability to absorb crystalline vitamin B12 remains intact in older people with atrophic gastritis. The 1998 recommended daily allowance for vitamin B12 is 2.4 micrograms, but elderly people should try to obtain their vitamin B12 from either supplements or fortified foods (e.g. fortified ready-to-eat breakfast cereals) to ensure adequate absorption from the gastrointestinal tract. Because the American food supply is now being fortified with folic acid, concern is increasing about neurologic exacerbation in individuals with marginal vitamin B12 status and high-dose folate intake.

Malabsorption of food cobalamin

Food-cobalamin malabsorption is marked by the inability to release cobalamin from food, which therefore cannot be taken up by intrinsic factor for absorption. The defect is not detectable by classical clinical tests like the Schilling test which are all based on the absorption of free, crystalline cobalamin. Tests of food-cobalamin absorption have been devised, the most popular ones using cobalamin bound to eggs or to chicken serum. The disparity between the abnormal results of these tests and the normal results with the Schilling test defines the disorder of food-cobalamin malabsorption. Release of cobalamin from food requires acid and pepsin, and most food-cobalamin malabsorptive states can be traced to gastric defects. However, other mechanisms may also play a role. The malabsorption is limited to food cobalamin and any free cobalamin, presumably including recycled biliary cobalamin, will be absorbed normally, which may explain its frequently insidious nature. The effect on cobalamin status covers a broad spectrum. At one extreme, some individuals, perhaps in the earliest stages, have normal cobalamin status, while at the other extreme may be found deficiency every bit as severe as in the most florid case of pernicious anaemia. Most often, however, the deficiency is mild, frequently marked by only a low serum cobalamin level, mild evidence of metabolic insufficiency and, sometimes, minimal clinical sequelae. Moreover, in some cases the gastric defect progresses and intrinsic factor secretion is affected, thus transforming into classical pernicious anaemia; this is not inevitable, however, and probably occurs in only a minority of patients. The course of food-cobalamin malabsorption is therefore a varied one. Nevertheless, it may be the most common cause of subtle or mild cobalamin deficiency and it is also sometimes associated with severe deficiency. Its identification and treatment need to be considered more widely in the clinical setting.

The effect of omeprazole on gastric acidity and the absorption of liver cobalamins

The effect of gastric anacidity on the absorption of food-bound cobalamins is uncertain. Omeprazole, an inhibitor of the enzyme H-K-ATPase in the parietal cell, is the most potent inhibitor of gastric acidity known so far. In 17 healthy male volunteers the absorption of liver-bound cobalamins was assessed after a single intravenous dose of omeprazole (80 mg) or placebo in a double-blind, crossover manner. The effect of omeprazole on pH, gastric acidity, and intrinsic factor (IF) concentration was measured in aspirates of gastric juice 5 min before and 30 and 60 min after the administration of liver homogenate containing 0.74 nmol of 57Co-labelled cobalamins. Omeprazole treatment resulted in anacidity (pH values above 6.0) in 14 individuals 30 min after the liver dose and in 15 individuals after 60 min. The IF concentration was unchanged in the omeprazole experiment as compared with the placebo experiment. The absorption of liver-bound cobalamins was 310 pmol (189-501 pmol) in the omeprazole experiment as compared with 415 pmol (150-549 pmol) in the placebo experiment (median values and range, p = 0.5228). We suggest that anacidity induced by omeprazole does not reduce the absorption of liver-bound cobalamins.

Clinically significant vitamin B12 deficiency secondary to malabsorption of protein-bound vitamin B12

Protein- (chicken serum) bound [57Co]cyanocobalamin absorption was evaluated in five hypochlorhydric patients who had developed B12 deficiency despite having normal absorption of unbound crystalline vitamin B12. All five patients had decreased urinary excretion of protein-bound B12 (0.06--0.34%) as compared to twelve normal controls (0.61--5.6%), P less than .001. Improvement in protein-bound B12 absorption in four of the five patients occurred with the exogenous administration of hydrochloric acid, pepsin, gastric intrinsic factor, or a combination thereof. Vitamin B12 deficiency developing in the setting of hypochlorhydria may result from deficiency of acid-peptic digestion of B12 bound to protein and/or a relative deficiency of intrinsic factor. This digestive defect is not detected with tests which measure the absorption of unbound crystalline B12 but is detected by a simple test which employs B12 bound to chicken serum as the form of protein-bound B12.

The forms of vitamin B12 in foods

1. The forms of vitamin B12 were determined in foods, most of which had been prepared for consumption. 2. Five forms were detected: adenosylcobalamin, hydroxocobalamin, methylcobalamin, cyanocobalamin and sulphitocobalamin. Adenoxylcobalamin and hydroxocobalamin were the predominant forms. 3. The intestinal absorption of [57Co]sulphitocobalamin was estimated and found to be lower than that of [58Co]cyanocobalamin.

Inhibitory effect of eggs on vitamin B12 absorption: description of a simple ovalbumin 57Co-vitamin B12 absorption test

Ovalbumin and egg yolks, mixed separately in vitro with radiocyanocobalamin (57 Co-vitamin B12), were served to normal volunteers in a cooked form. Ovalbumin, and to a lesser degree, egg yolks were observed to inhibit vitamin B12 absorption. This observation explains the rather poor assimilation of vitamin B12 from eggs labelled in vivo with 57 Co-vitamin B12.