Brief Critical Review

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1 Brief Critical Review October 2007: If High Folic Acid Aggravates Vitamin B 12 Deficiency What Should Be Done About It? Mary Ann Johnson, PhD The most common cause of vitamin B 12 deficiency in older people is malabsorption of food-bound vitamin B 12. Thus, it is suggested that the recommended daily allowance of 2.4 g/d be met primarily with crystalline vitamin B 12, which is believed to be well absorbed in individuals who have food-bound malabsorption. There is concern that high intakes of folic acid from fortified food and dietary supplements might mask the macrocytic anemia of vitamin B 12 deficiency, thereby eliminating an important diagnostic sign. One recent study indicates that high serum folate levels during vitamin B 12 deficiency exacerbate (rather than mask) anemia and worsen cognitive symptoms. Another study suggests that once vitamin B 12 deficiency is established in subjects with food-bound malabsorption, 40 g/d to 80 g/d of oral crystalline vitamin B 12 for 30 d does not reverse the biochemical signs of deficiency. Together, these studies provide further evidence that public health strategies are needed to improve vitamin B 12 status in order to decrease the risk of deficiency and any potentially adverse interactions with folic acid. Key words: cognition, fortification, homocystein 2007 International Life Sciences Institute doi: /nr.2007.oct INTRODUCTION Vitamin B 12 functions in two mammalian enzymes and is essential for cognition, the nervous system, vascular health, and synthesis of red blood cells. 1-4 During vitamin B 12 deficiency, decreased activity of methionine synthase may cause trapping of folate as methylfolate. Dr. Johnson is with the Department of Foods and Nutrition, University of Georgia, Athens, Ga, USA. Please direct all correspondence to Dr. Mary Ann Johnson, Professor of Foods and Nutrition and Faculty of Gerontology, Department of Foods and Nutrition, Dawson Hall, Building 1010, University of Georgia, Athens, GA , USA. Phone: ; Fax: ; mjohnson@fcs.uga.edu One consequence of this is that the methyl group is not available to methylate homocysteine, which leads to decreased synthesis of methionine, S-adenosylmethionine, and other components of the methylation cycle, as well as high levels of serum homocysteine. Impaired activity of the vitamin B 12 -dependent enzyme methylmalonyl-coenzyme A-mutase leads to a high level of serum methylmalonic acid, which is useful for the diagnosis of vitamin B 12 deficiency. VITAMIN B 12 INTAKE AND STATUS The prevalence of vitamin B 12 deficiency in older adults ranges from 5% to more than 20% depending on the population and the criteria used for assessment. 1-3,5 The primary cause of vitamin B 12 deficiency is atrophic gastritis, which occurs in 10 30% of older adults. Atrophic gastritis leads to decreased gastric acid, digestive enzymes, and the ability to digest the food-bound forms of vitamin B 12 in meat, poultry, fish, and dairy foods. Another cause of vitamin B 12 deficiency is pernicious anemia, which occurs in about 1 2% of older adults and is associated with loss of the intrinsic factor needed for vitamin B 12 absorption. About 1% of oral vitamin B 12 can be absorbed passively without intrinsic factor, so it is suggested that high oral doses of vitamin B 12 can meet the estimated metabolic requirement of 1 g/d; typically, oral doses of g/d are recommended to treat deficiency. 3,6 The recommended dietary allowance (RDA) for vitamin B 12 is 2.4 g/d and it is recommended that the majority be consumed as crystalline vitamin B 12, because the absorption of this form is apparently not affected by atrophic gastritis. The median dietary intakes of vitamin B 12 in women and men aged 60 years are 2.7 g/d and 3.9 g/d, respectively, 7 but the intake of crystalline vitamin B 12 from fortified foods and dietary supplements has not been well quantified in the US population. Multivitamins for older adults generally contain 6 g to30 g, while the few foods that are vitamin B 12 -fortified typically contain 2.5 g to6 g. Folate is a general term for the vitamin present in many chemical forms and that functions in single-carbon Nutrition Reviews, Vol. 65, No

2 transfer reactions. 1,4 Folic acid (pterolymonoglutamic acid) is the most oxidized and stable form of folate and it is rarely present naturally in food. Folic acid is the chemical form of folate added to fortified foods and dietary supplements; it is absorbed to a higher degree than the naturally occurring food folates. 1 Naturally occurring food folates are pterolpolyglutamates that contain several additional glutamate molecules. Food folates are hydrolyzed to monoglutamate forms in the gut before absorption across the intestinal mucosa occurs. The monoglutamate form is actively transported across the proximal small intestine by a saturable process; pharmacological amounts of the monoglutamate form are absorbed by a nonsaturable process involving passive diffusion. Monoglutamates, primarily in the form of 5-methyl-tetrahydrofolate, are present in the portal circulation, and much of this is taken up by the liver, where folate is metabolized to polyglutamate derivatives and retained or released into the blood or bile. The main circulating forms are 5-methyl-tetrahydrofolate compounds. Folic acid-fortified foods such as breads, pasta, and some cereals typically provide about 40 g per serving. Highly fortified breakfast cereals, most multivitamins, and most B-complex vitamins contain 400 g of folic acid per serving or tablet. The RDA for men and women from the age of 14 years to 70 years is 400 dietary folate equivalents, which is equal to 400 g of naturally occurring food folates or about 240 g of folic acid in fortified foods. 1 In addition, to reduce the risk of neural tube defects (NTD) it is recommended that women capable of becoming pregnant consume 400 g/d of folic acid from fortified foods and/or a supplement as well as food folate from a varied diet. 1 The upper level is expressed as 1000 g/d of folic acid from fortified foods and/or supplements for adults aged 19 years and older. 1 In the National Health and Nutrition Examination Survey (NHANES) conducted in (post-mandatory folic acid fortification), the median folate intake from food in adults aged 60 years was 275 g/d in women and 351 g/d in men; % took multivitamins and 7.2% took B-complex vitamins. 8 In analyses that corrected for the measurement error related to NHANES methodology, it was estimated that total folate consumption (including natural folate and folate in fortified foods and dietary supplements) in subjects aged 65 years exceeds 1000 g/d in about 2 4% of men and 1 4% of women; uncorrected estimates ranged up to 8%. 9 In 1998, mandatory folic acid fortification of cereal grain products went into effect in the US. 10 The purpose of folic acid fortification is to decrease the incidence of NTD 10 and this is being achieved. 11 Another benefit of folic acid fortification may be decreased incidence of stroke. 12,13 Randomized, controlled trials suggested that folic acid supplementation (800 g/d for 3 years) maintained several aspects of cognitive function that tend to decline with age 14 and decreased the progression of age-related hearing loss. 15 POTENTIAL RISKS OF HIGH FOLIC ACID INTAKE Despite these apparent benefits of improved folate status, there may be risks associated with high intakes of folic acid Folic acid can be detected in serum. For example, after 14 weeks of consuming 400 g of folic acid daily, total folate concentration in subjects serum was found to be 33.5 nmol/l and folic acid concentration in serum was 0.48 nmol/l (1.4% of total folate). 21 Compared to this long-term study, 21 acute dosing with folic acid followed by blood collection over the next few hours revealed higher amounts of folic acid in the serum. 22 The toxicity of detectable folic acid in serum and of high folic acid intake in general is unclear and controversial ,23,24 The increase in serum folate in response to folic acid supplementation is much higher in older people than in younger people. 19 A recent randomized clinical trial suggested that folic acid supplementation (1000 g/d for 6 years) increased the risk of some types of colorectal neoplasia in those with a recent history of colorectal adenomas. 25 DOES HIGH SERUM FOLATE EXACERBATE VITAMIN B 12 DEFICIENCY? There is also continued concern that high intakes of folic acid may appear to prevent and/or cure the macrocytic anemia often associated with vitamin B 12 deficiency. This effect, known as masking of vitamin B 12 deficiency, is important because the deficiency is often initially detected by measuring the level of macrocytic red blood cells. However, Mills et al. 26 reported no change in the prevalence of anemia among subjects in the US with low serum vitamin B 12 after food fortification. Vitamin B 12 fortification of the food supply has been recommended, but the suggested target intake is unclear, ranging from 1 g/d to 15 g/d. 23,27 Improved vitamin B 12 status through supplementation and/or fortification would help alleviate the risk of folic acid masking vitamin B 12 deficiency. Improved vitamin B 12 status may also decrease the risk of NTD. 28 Two studies with implications regarding folic acid fortification and vitamin B 12 deficiency in older adults are reviewed below. The results of the first study suggest that during vitamin B 12 deficiency, high serum folate levels exacerbate (rather than mask) anemia and also exacerbate cognitive symptoms. 29 The second study was a dose-finding trial conducted to quantify the relationship between oral vitamin B 12 intake and serum vitamin B Nutrition Reviews, Vol. 65, No. 10

3 Table 1. High serum folate may worsen the anemia and cognitive impairment associated with vitamin B 12 deficiency in older adults (NHANES ) Adverse outcome B 12 * Folate N Adverse outcome (N) Adverse outcome (%) High homocysteine (%) OR (95%CI) full model Anemia Adequate Normal Anemia Adequate High (0.2, 2.4) Anemia Deficient Normal (1.01, 3.6) Anemia Deficient High (2.3, 10.4) Cognitive impairment Adequate Normal Cognitive impairment Adequate High (0.2, 0.96) Cognitive impairment Deficient Normal (0.95, 2.8) Cognitive impairment Deficient High (2.6, 9.2) *Low serum vitamin B 12 status defined as serum vitamin B pmol/l or serum MMA 210 nmol/l. High folate status defined as serum folate 59 nmol/l (80 th percentile). Adjusted for age, sex, race-ethnicity, educational status, cancer history, diabetes status, hyperhomocysteinemia ( 13 mol/l), and serum concentrations of ferritin, creatinine, and glucose. Anemia defined as hemoglobin 120 g/l in women and 130 g/l in men. Cognitive impairment defined as 34, lower 20 th percentile, on a version of the Wechsler Adult Intelligence Scale III (maximum 133) Reprinted with permission from Morris et al. 29 Am J Clin Nutr. 2007;85: , American Society for Nutrition in individuals with food-bound vitamin B 12 malabsorption; 30 this information can begin to identify the intake of oral crystalline vitamin B 12 that might optimize vitamin B 12 status, helping to eliminate concerns about the adverse effects of folic acid. Morris et al. 29 examined the associations among serum folate, vitamin B 12 deficiency, anemia, and cognitive impairment in older adults in NHANES in the age of folic acid fortification. Inclusion criteria included normal serum creatinine concentrations and no history of stroke, heavy alcohol use, recent anemia therapy, or disease of the liver, thyroid, or coronary arteries. Of the 3706 older adults in the survey, 1684 were eligible, 1078 were ineligible, and the eligibility status of 944 could not be determined. Sample sizes for analyses of anemia and cognitive impairment were 1458 and 1302, respectively. Anemia was defined as hemoglobin 120 g/l for women and 130 g/l in men. Cognitive status was assessed using a version of the Digit Symbol-Coding subtest of the Wechsler Adult Intelligence Scale III. According to the authors documentation, 29 this test involves copying symbols that are paired with numbers, is timed for a maximum of 120 seconds, has a maximum score of 133, and some evidence suggests it is superior to the Mini-Mental State Examination for detecting some signs of dementia. The test assesses speed, sustained attention, visual spatial skills, associative learning, and memory, with speed being one of the primary determinants of test performance. Cognitive impairment was defined as having a test score of 34, which was the 20 th percentile of the distribution. Serum folate and vitamin B 12 were assessed using radioassay (Quantaphase II Radioassay Kit, Bio-Rad Laboratories, Anaheim, Calif., United States). Vitamin B 12 deficiency was defined as either 1) serum vitamin B 12 of 148 pmol/l or 2) serum methylmalonic acid 210 nmol/l, which is the reference range for vitamin B 12 -replete individuals with normal serum creatinine (note that the MMA methodology differs among NHANES surveys, so the results of various studies may not be comparable). High serum folate was defined as 59 nmol/l, which reflects the 80 th percentile distribution in older adults; in some analyses to detect interactions, serum folate was also used as a continuous variable. Univariate analyses identified several differences between those with adequate and deficient vitamin B 12 status. Those with vitamin B 12 deficiency were significantly older (72 y vs 70 y) and had lower serum folate (34 vs 39 nmol/l). They were less likely to be male (34% vs 38%), be non-hispanic black (4.4% vs 8%), have a high school diploma (68% vs 75%), and use supplements (54% vs 71%). They were more likely to smoke (17% vs 12%) and have macrocytosis (6.5% vs 2.7%), anemia (8.3% vs 3.2%), and cognitive impairment (32% vs 15%). A series of multivariate analyses controlling for several demographic and health-related indices were conducted to identify the relationships of folate and vitamin B 12 status with anemia, cognitive impairment, and homocysteine. The prevalence of anemia in participants with normal vitamin B 12 status was about 3% and was not affected by folate status (Table 1). However, a significant interaction between folate and vitamin B 12 status occurred, such that the deficient vitamin B 12 /high- Nutrition Reviews, Vol. 65, No

4 folate group was about twice as likely to be anemic compared to the deficient vitamin B 12 /normal-folate group (15% vs 6.9%). A statistically significant interaction also occurred for cognitive impairment; in vitamin B 12 -adequate participants, higher folate status was associated with better cognitive status, but in vitamin B 12 - deficient participants, the prevalence of cognitive impairment was nearly double in those with high versus normal folate status (45% vs 25%). High homocysteine did not closely track the prevalence of anemia or cognitive impairment; for example, the highest percentage of high homocysteine did not occur in the group with the highest prevalence of anemia or cognitive impairment. Comments It was unexpected that high serum folate coexisting with vitamin B 12 deficiency would worsen both anemia and cognitive impairment. Thus, even though the regression analyses controlled for several potentially important predictors of anemia and cognition, there are some concerns about whether or not a few individuals in the small vitamin B 12 -deficient/high-folate group may have had some unusual characteristics that skewed the results and contributed to the interaction. Specific questions include the following. 1) Could the overall findings be related to the relatively small sample size of the vitamin B 12 -deficient/high folate group (N 42 49) compared to the other participants (N )? a) In the vitamin B 12 -deficient/ high-folate group versus the other participants, the number of cases of anemia was 7 versus 57 and the number of cases of cognitive impairment was 19 versus 230. b) Even though demographic characteristics were included in the multivariate regression models, perhaps there were some demographic differences in this small group that may have magnified their response to high folic acid. For example, compared to blacks, whites have better folate status, but poorer vitamin B 12 status. 5,31,32 2) Did the causes of high serum folate differ in the vitamin B 12 -deficient/high-folate group compared to the vitamin B 12 -adequate/high-folate group? a) Was the vitamin B 12 -deficient/high-folate group consuming large amounts of folic acid from supplement formulations that may have contributed to the anemia or cognitive impairment, e.g., folic acid supplements with minimal vitamin B 12 and/or iron? Some dietary supplements marketed to older adults contain minimal or no iron. Also, the amount of vitamin B 12 in B complex supplements ranges from about 6 g to100 g, while the amount of folate is usually 400 g/tablet. b) Was the vitamin B 12 -deficient/ high-folate group consuming large amounts of folic acid from fortified foods formulated in such a way as to worsen the anemia or cognitive impairment, e.g., breakfast cereals with high amounts of folic acid (e.g., 400 g per serving) with minimal vitamin B 12 and/or poorly available iron? c) Did the vitamin B 12 -deficient/highfolate group have a high prevalence or severity of an undetected infection that might have increased their serum folate? For example, infection with tick-borne fever caused by rickettsia Anaplasma phagocytophilum in sheep led to unusually high serum folate concentrations (in the 300 to 400 nmol/l range). 33 Also, increased serum folate and decreased serum vitamin B 12 have each been associated with small intestinal bacterial overgrowth in animals, because many enteric bacteria synthesize folate that is available for absorption, but bind vitamin B 12, which is then unavailable for uptake in the ileum; 34 similar processes can occur in vitamin B 12 - deficient humans. 2 3) What were the primary causes of vitamin B 12 deficiency in the vitamin B 12 -deficient/high-folate group and did they differ from the vitamin B 12 -adequate/highfolate group? Perhaps the vitamin B 12 -deficient/highfolate group was simply the most vitamin B 12 -deficient. Possibly, the vitamin B 12 -deficient/high-folate, compared to the vitamin B 12 -deficient/normal-folate group were: a) more likely to lack intrinsic factor, suggesting a more long-standing and severe form of vitamin B 12 deficiency that would, in turn, explain the higher prevalence of anemia and cognitive impairment; or b) more likely to have a lower serum vitamin B 12 level, intake of total vitamin B 12, and/or intake of synthetic vitamin B 12, which might also indicate a more long-standing and severe form of vitamin B 12 deficiency. 4) What was the nature and severity of the anemia in the vitamin B 12 -deficient/high-folate group compared to the vitamin B 12 -deficient/normal-folate group? a) Could there be a higher prevalence of iron deficiency-related anemia that might contribute to both the higher prevalence of anemia and cognitive impairment? Vitamin B 12 deficiency has been associated with low serum ferritin in older adults 5 and was seen in the present study as well (although it was controlled in the regression analyses). b) Could there be a higher prevalence of anemia of chronic disease that might contribute to both the higher prevalence of anemia and possibly cognitive impairment? c) Was there a higher prevalence of gastrointestinal bleeding that could have contributed to the anemia? In summary, while the vitamin B 12 -deficient/highfolate group clearly had the highest prevalence of anemia and cognitive impairment among the four vitamin B 12 / folate groups in this study, the individual cases of vitamin B 12 deficiency could be explored further. Also, the findings need replication in other studies that include detailed analyses of the dietary and supplement use patterns, as well as the causes and severity of vitamin B 12 deficiency, anemia, and cognitive impairment. 454 Nutrition Reviews, Vol. 65, No. 10

5 WHAT IS THE OPTIMAL INTAKE OF CRYSTALLINE VITAMIN B 12 IN ELDERLY PEOPLE WITH MALABSORPTION OF FOOD- BOUND VITAMIN B 12? Table 2. Baseline characteristics of 67 elderly subjects with vitamin B 12 malabsorption from food Characteristic Value (mean SD) Age, y Gender, % female 57 Hemoglobin, g/l Mean corpuscular volume, fl Serum vitamin B 12, pmol/l* Plasma folate, nmol/l Folate deficiency, % 76 Plasma homocysteine, mol/l Plasma methylmalonic acid, nmol/l Total vitamin B 12 intake, g/d Total folate intake, g/d *Normal 162 pmol/l Folate deficiency defined as plasma folate 6.8 nmol/l Normal 14.6 mol/l Normal 2250 nmol/l Data adapted with permission from Blacher et al. 30 J Nutr. 2007;137: , American Society for Nutrition It is recommended that 2.4 g/d of crystalline vitamin B 12 will meet the requirements for those with malabsorption of food-bound vitamin B 12 in animal foods. 1 However, Campbell et al. 35 found in the Sacramento Area Latino Study on Aging that 14% of those consuming 2.4 g of crystalline vitamin B 12 from supplements and fortified foods had plasma vitamin B 12 concentrations 148 pmol/l (i.e., in the deficient range). Also, in several other cross-sectional surveys of older adults, the risk of poor vitamin B 12 status, as assessed by serum or plasma vitamin B 12 and/or methylmalonic acid, was not less than 5% until the consumption of vitamin B 12 was 9 g/d, g/d, 36 or g/d. 37 Because 2.4 g/d appears to offer inadequate protection against vitamin B 12 deficiency in these cross-sectional studies, there is interest in conducting clinical trials to quantify the requirements for crystalline vitamin B 12 in those with malabsorption of food-bound vitamin B 12. In one such study, Blacher et al. 30 randomly assigned people with food-bound vitamin B 12 malabsorption from a frail geriatric population to one of six oral daily doses of vitamin B 12 (2.5, 5, 10, 20, 40, and 80 g/d) for 30 d to identify the dose that increased serum vitamin B 12 by 37 pmol/l (50 ng/ml). Every person entering the Emile Roux Hospital in a suburb of Paris between June 2003 and March 2004 was screened for vitamin B 12 status. Those with low serum vitamin B 12 ( 162 pmol/l) were identified and the following inclusion criteria were applied: 1) 70 y of age; 2) absence of fatal disease, life expectancy 1 month; 3) planned hospitalization duration of 1 month; 4) lack of clinical signs of vitamin B 12 deficiency (i.e., Mini Mental Status Examination 23 of 30 points, absence of clinical peripheral neuropathy, absence of clinical signs of subacute combined degeneration of the spinal cord, hemoglobin 100 g/l). Participants also had to show evidence of food-bound vitamin B 12 malabsorption, such as 1) low serum vitamin B 12 concentration; 2) normal Schilling s test; and 3) no dietary vitamin B 12 deficiencies and at least one of the following conditions: a) gastric disease, including atrophic gastritis, type A atrophic gastritis, gastric disease associated with Helicobacter pylori infection, partial gastrectomy, bypass gastric surgery, vagotomy, or Zollinger-Ellison syndrome; b) pancreatic insufficiency resulting from alcohol abuse or cystic fibrosis; c) gastric or intestinal bacterial overgrowth, including achlorhydria, sprue tropical, Ogilvie syndrome; d) chronic drug treatment such as ingestion of acid-suppressing drugs or biguanides (metformin); e) alcohol abuse; or f) aging. Of the 1277 subjects initially screened, 190 had low serum vitamin B 12 ( 162 pmol/l; yielding a 14.9% prevalence of deficiency), 26 refused to participate, and 89 met all of the inclusion criteria and were randomized to the treatments (two subjects with positive intrinsic factor antibody were kept in the analysis because they responded to oral vitamin B 12 similarly to the other study participants). The baseline characteristics of the 67 participants who completed the intervention are shown in Table 2. Vitamin B 12 in the oral supplements was verified by HPLC and was administered to the participants under supervision of the medical staff, who were unaware of treatment assignation. For ethical reasons, the treatment period was limited to 30 d. Dose-response analyses were performed using a mixed model, taking into account the initial value, a linear log-dose effect, and a linear log-dose time interaction, where time was 15 or 30 d. From these analyses, it was estimated that 5.9 g/d of vitamin B 12 would increase serum vitamin B 12 by 37 pmol/l, thus increasing serum vitamin B 12 from about 111 pmol/l (typical serum vitamin B 12 in deficient patients from other published literature) to 148 pmol/l or above, which the authors indicated would be normal according to their criteria. Changes in serum vitamin B 12 are shown in Figures 1A and 1B. The 40 g/d and 80 g/d doses were clearly superior to the lower doses (Figure 1A). Perhaps the small sample sizes within each treatment (N 8 to 12) contributed to the inconsistent and low response to the 5 g/d dose (Figure 1B). Additional studies in those Nutrition Reviews, Vol. 65, No

6 Serum B12 (pmol/l) Change in Serum B12 (pmol/l) with food-bound malabsorption are needed to clarify the dose-response relationships of oral doses of vitamin B 12 of 20 g/d, especially if recommendations for fortification and/or supplementation are set below 20 g/d for this subgroup of the older adult population. Comments Baseline Day 15 Day Supplemental B12 (µg/d) Figure 1. Increase (A) and change (B) in serum vitamin B 12 after 15 and 30 days of supplementation in vitamin B 12 - deficient participants with food-bound malabsorption of vitamin B 12. Participants were randomly assigned to one of six oral daily doses of vitamin B 12 (2.5, 5, 10, 20, 40, and 80 g/d) in order to identify the dose that increased serum vitamin B 12 by 37 pmol/l (50 ng/ml). Data adapted with permission from Blacher et al. 30 J Nutr. 2007;137: , American Society for Nutrition The main strength of the Blacher et al. 30 study is that it documents the pervasiveness of vitamin B 12 deficiency in hospitalized older adults, as well as the very high prevalence of folate deficiency when the food supply is not fortified with folic acid. Some difficulties in using data from these types of dose-finding trials to develop food-fortification and supplement-use recommendations is that the severe degree of deficiency means that the doses are probably replenishing both the metabolically active body pool as well as body stores. Also, there is no A B consensus on what constitutes an adequate or optimal serum concentration of vitamin B 12. The authors goal of reaching 148 pmol/l seems rather low, given that some signs of vitamin B 12 deficiency can occur when serum vitamin B 12 concentrations are up to 258 pmol/l. 5,31,38 The response of serum vitamin B 12 to oral vitamin B 12 was the same at the 40 g/d and 80 g/d doses after 30 d, and final concentrations averaged only about 200 pmol/l (Figure 1A). In addition, these doses of vitamin B 12 did not lower the markedly elevated serum methylmalonic acid, probably for one or more of the following reasons: 1) the doses were too low; 2) renal insufficiency led to decreased renal clearance of methylmalonic acid; and/or 3) intestinal bacteria was the source of methylmalonic acid. If the participants had bacterial overgrowth of the intestine, then some circulating methylmalonic acid may have been derived from this microbial source and may have been unresponsive to increased intake of vitamin B The lack of change in serum homocysteine is not surprising given the high prevalence of folate deficiency in this population unexposed to folic acid fortification (76%) and the possibility of renal insufficiency. Eussen et al. 40 reported that community-dwelling older adults with initial serum vitamin B 12 concentrations of about 208 pmol/l (range pmol/l) needed a dose of 100 g/d for 8 weeks to improve serum vitamin B 12 to about 300 pmol/l, but a dose of more than 500 g/d for 8 16 weeks was needed to maximally lower serum methylmalonic acid. PUBLIC HEALTH IMPLICATIONS Together, the studies of Morris et al. 29 and Blacher et al. 30 provide further evidence of the need to implement public health strategies to improve vitamin B 12 status in older adults. Cross-sectional studies suggest that supplements containing vitamin B 12 decrease the prevalence of vitamin B 12 deficiency. 31,35-37 Vitamin B 12 fortification of the food supply has also been recommended, but there is no clear consensus on the appropriate target intake or fortification level. Estimates in the low range include 1 g/d to provide a portion of the RDA of 2.4 g/d. 27 Higher estimates in the range of 12 g/d to 15 g/d are recommended to increase body stores of vitamin B 12 to be available when intrinsic factor is lost and the capacity to absorb vitamin B 12 is diminished. 23 The findings of Blacher et al. 30 show that once an older adult with food-bound vitamin B 12 malabsorption becomes extremely deficient, intakes of vitamin B 12 of 20 g/d are unlikely to normalize serum vitamin B 12 or methylmalonic acid in the short term. The goals of a vitamin B 12 -fortification or supplement-use program will need clarification regarding the 456 Nutrition Reviews, Vol. 65, No. 10

7 target levels of serum vitamin B 12, serum methylmalonic acid, and liver stores of vitamin B 12 to provide the metabolic needs for vitamin B 12 when absorption begins to fail due to food-bound malabsorption and/or pernicious anemia. Improved vitamin B 12 status would help alleviate any effect of folic acid in aggravating vitamin B 12 deficiency. Also, improved vitamin B 12 status, by lowering the risk of NTD, may promote health in other age groups. 28 ACKNOWLEDGMENTS The editorial assistance of Dr. Dorothy B. Hausman is greatly appreciated. REFERENCES 1. Institute of Medicine. Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, Folate, Dietary reference intakes for thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B 12, pantothenic acid, biotin, and choline. Washington, DC: National Academy Press, 1998: Baik HW, Russell RM. Vitamin B 12 deficiency in the elderly. Ann Rev Nutr. 1999;19: Stabler SP. Vitamin B-12. In: Bowman BA, Russell RM, ed. Present Knowledge in Nutrition, 8 th edition. Washington, DC, ILSE Press; 2001: Stover PJ. Physiology of folate and vitamin B 12 in health and disease. Nutr Rev. 2004;62(Suppl):S3 S Johnson MA, Hawthorne NA, Brackett WR, et al. Hyperhomocysteinemia and vitamin B 12 deficiency in elders using Title IIIc Nutrition Services. Am J Clin Nutr. 2003;77: Kuzminski AM, Del Giacco EJ, Allen RH, Stabler SP, Lindenbaum J. Effective treatment of cobalamin deficiency with oral cobalamin. Blood. 1998;92: Ervin RB, Wright JD, Wang CY, Kennedy-Stephenson J. Dietary intake of selected vitamins for the United States population: Advance Data from Vital and Health Statistics. 2004;339:1 4. Available at ad339.pdf. Accessed August 24, Radimer K, Bindewald B, Hughes J, Ervin B, Swanson C, Picciano MF. Dietary supplement use by US adults: data from the National Health and Nutrition Examination Survey, Am J Epidemiol. 2004;160: Bentley TG, Willett WC, Weinstein MC, Kuntz KM. Population-level changes in folate intake by age, gender, and race/ethnicity after folic acid fortification. Am J Public Health. 2006;96: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Recommendations for the use of folic acid to reduce the number of cases of spina bifida and other neural tube defects. MMWR. 1992;41(RR-14): U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Spina bifida and anencephaly before and after folic acid mandate United States, and MMWR 2004;53: Yang Q, Botto LD, Erickson JD, Berry RJ, Sambell C, Johansen H, Friedman JM. Improvement in stroke mortality in Canada and the United States, 1990 to Circulation. 2006;113: Wang X, Qin X, Demirtas H, Li J, Mao G, Huo Y, Sun N, Liu L, Xu X. Efficacy of folic acid supplementation in stroke prevention: a meta-analysis. Lancet. 2007; 369: Durga J, van Boxtel MP, Schouten EG, Kok FJ, Jolles J, Katan MB, Verhoef P. Effect of 3-year folic acid supplementation on cognitive function in older adults in the FACIT trial: a randomised, double blind, controlled trial. Lancet. 2007;369: Durga J, Verhoef P, Anteunis LJ, Schouten E, Kok FJ. Effects of folic acid supplementation on hearing in older adults: a randomized, controlled trial. Ann Intern Med. 2007;146: Hubner RA, Houlston RD, Muir KR. Should folic acid fortification be mandatory? No. BMJ. 2007;334: Reynolds EH. Benefits and risks of folic acid to the nervous system. J Neurol Neurosurg Psychiatry. 2002;72: Smith AD. Folic acid fortification: the good, the bad, and the puzzle of vitamin B-12. Am J Clin Nutr. 2007;85: Wald NJ, Law MR, Morris JK, Wald DS. Quantifying the effect of folic acid. Lancet. 2001;358: Review. Erratum in: Lancet 2002;359: Wald NJ, Oakley GP. Should folic acid fortification be mandatory? Yes. BMJ. 2007;334: Sweeney MR, McPartlin J, Scott J. Folic acid fortification and public health: report on threshold doses above which unmetabolised folic acid appear in serum. BMC Public Health. 2007;7: Sweeney MR, McPartlin J, Weir DG, Daly L, Scott JM. Postprandial serum folic acid response to multiple doses of folic acid in fortified bread. Br J Nutr. 2006;95: Oakley GP, Jr. Oral synthetic folic acid and vitamin B 12 supplements work if one consumes them. Nutr Rev. 2004;62(Suppl):S22 S Shane B. Folate fortification: enough already? Am J Clin Nutr. 2003;77: Cole BF, Baron JA, Sandler RS, Haile RW, Ahnen DJ, Bresalier RS, McKeown-Eyssen G, et al.; Polyp Prevention Study Group. Folic acid for the prevention of colorectal adenomas: a randomized clinical trial. JAMA. 2007;297: Mills JL, Von Kohorn I, Conley MR, Zeller JA, Cox C, Williamson RE, Dufour DR. Low vitamin B-12 concentrations in patients without anemia: the effect of folic acid fortification of grain. Am J Clin Nutr. 2003; 77: Executive Summary. Recommended levels of folic acid and vitamin B 12 fortification: conclusions. Nutr Rev. 2004;62(Suppl):S62 S Ray JG, Wyatt PR, Thompson MD, Vermeulen MJ, Meier C, Wong PY, Farrell SA, Cole DE. Vitamin B 12 and the risk of neural tube defects in a folic-acidfortified population. Epidemiology. 2007;18: Morris MS, Jacques PF, Rosenberg IH, Selhub J. Folate and vitamin B-12 status in relation to anemia, Nutrition Reviews, Vol. 65, No

8 macrocytosis, and cognitive impairment in older Americans in the age of folic acid fortification. Am J Clin Nutr. 2007;85: Blacher J, Czernichow S, Raphael M, Roussel C, Chadefaux-Vekemans B, Morineau G, Giraudier S, et al. Very low oral doses of vitamin B-12 increase serum concentrations in elderly subjects with foodbound vitamin B-12 malabsorption. J Nutr. 2007; 137: Stabler SP, Allen RH, Fried LP, Pahor M, Kittner SJ, Penninx WJH, Guralnik JM. Racial differences in prevalence of cobalamin and folate deficiencies in disabled elderly women. Am J Clin Nutr. 1999;70: Pfeiffer CM, Caudill SP, Gunter EW, Osterloh J, Sampson EJ. Biochemical indicators of B vitamin status in the US population after folic acid fortification: results from the National Health and Nutrition Examination Survey Am J Clin Nutr. 2005;82: Kleppa KE, Stuen S. High serum folate values in lambs experimentally infected with Anaplasma phagocytophilum. Act Vet Scand ;44; Merck Veterinary Manual, Malabsorption Syndromes, 2006, Merck & Co., Inc., Whitehouse Station, NJ USA. Available at: index.jsp?cfile htm/bc/23313.htm. Accessed August 24, Campbell AK, Miller JW, Green R, Haan MN, Allen LH. Plasma vitamin B-12 concentrations in an elderly Latino population are predicted by serum gastrin concentrations and crystalline vitamin B-12 intake. J Nutr. 2003;133: Rajan S, Wallace JI, Beresford SA, Brodkin KI, Allen RA, Stabler SP. Screening for cobalamin deficiency in geriatric outpatients: prevalence and influence of synthetic cobalamin intake. J Am Geriatr Soc. 2002; 50: Garcia A, Paris-Pombo A, Evans L, Day A, Freedman M. Is low-dose oral cobalamin enough to normalize cobalamin function in older people? J Am Geriatr Soc. 2002;50: Allen RH, Stabler SP, Savage DG, et al. Elevation of 2-methylcitric acid I and II levels in serum, urine, and cerebrospinal fluid of patients with cobalamin deficiency. Metabolism. 1993;42: Lindenbaum J, Savage DG, Stabler SP, Allen RH. Diagnosis of cobalamin deficiency: II. Relative sensitivities of serum cobalamin, methylmalonic acid, and total homocysteine concentrations. Am J Hematol. 1990;34: Eussen SJ, de Groot, LC, Clarke R, et al. Oral cyanocobalamin supplementation in older people with vitamin B 12 deficiency. Arch Intern Med. 2005; 165: Nutrition Reviews, Vol. 65, No. 10

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