Preventive Medicine 39 (2004) 1256 – 1266 www.elsevier.com/locate/ypmed Review Cobalamin: a critical vitamin in the elderly Maike Wolters, Ph.D., * Alexander Ströhle, Ph.D-student, and Andreas Hahn, Prof. Nutrition Physiology and Human Nutrition Unit, Department of Food Science, Centre of Applied Chemistry, University of Hanover, D-30453 Hannover, Germany Available online 11 June 2004 Abstract Vitamin B12 deficiency is a common problem in elderly subjects. If a serum cobalamin level of about 150 pmol/L (200 pg/mL) is considered normal, 10 – 15% of the elderly are deficient. Today, however, a threshold of 220 – 258 pmol/L (300 – 350 pg/mL) is recognized as desirable in the elderly, or else sensitive markers like the blood concentration of homocysteine or methylmalonic acid (MMA) are used. Then the prevalence of cobalamin deficiency rises to up to 43%. In the elderly, this high prevalence of poor cobalamin status is predominantly caused by atrophic gastritis type B. Atrophic gastritis results in declining gastric acid and pepsinogen secretion, and hence decreasing intestinal absorption of the cobalamin protein complexes from food. About 20 – 50% of the elderly are affected. Furthermore, the reduced acid secretion leads to an alkalinization of the small intestine, which may result in bacterial overgrowth and thus to a further decrease of the bioavailability of the vitamin. In addition, some drugs such as proton pump inhibitors or H2 receptor antagonists inhibit the intestinal absorption of vitamin B12. An already moderately reduced vitamin B12 level is associated with vascular disease and neurocognitive disorders such as depression and impaired cognitive performance. Furthermore, a poor vitamin B12 status is assumed to be involved in the development and progression of dementia (e.g., Alzheimer’s dementia). This is especially observable if the folic acid status is reduced as well. Due to the insecure supply, the cobalamin status of elderly persons (z60 years) should be regularly controlled and a general supplementation with vitamin B12 (>50 Ag/day) should be considered. D 2004 The Institute For Cancer Prevention and Elsevier Inc. All rights reserved. Keywords: Vitamin B12; Cobalamin; Homocysteine; Methylmalonic acid; Elderly; Atrophic gastritis; Vitamin – drug interactions; Atherosclerosis; Neurocognitive function Introduction There is a variety of reasons why elderly, especially geriatric subjects, are at high risk for nutrient deficiencies including age-associated physiological changes, chronic diseases, and a high prevalence of drug intake. Vitamin B12 deficiency is one of the most important problems in the nutrition of the elderly [1,2] since the absorption of cobalamin is often reduced in this group [3,4]. Current investigations indicate that insufficient vitamin B12 status may increase the risk for atherosclerotic [5– 7] and neurodegenerative diseases [2,8]. In the meanwhile, several nutrition boards recommend monitoring the vitamin B12 status of elderly people and identifying risk persons at an early stage. * Corresponding author. Institute of Food Science, Department of Applied Chemistry, University of Hannover, Wunstorfer Str. 14, D-30453 Hannover, Germany. Fax: +49-511-762-5729. E-mail address: maike.wolters@lw.uni-hannover.de (M. Wolters). The aim of this review is to describe the age-associated changes in cobalamin metabolism and to show pathophysiological and therapeutic consequences. Metabolic function and sources of vitamin B12 Vitamin B12 contains a cobalt-centered corrin nucleus and shows a complex structure. The term vitamin B12 includes all corrinoids qualitatively exhibiting the biological activity of cyanocobalamin. The coenzymatically active forms of vitamin B12 are adenosylcobalamin and methylcobalamin, which are involved in two enzymatic reactions in human metabolism. One reaction requiring methylcobalamin is the remethylation of homocysteine to methionine catalyzed by the methionine synthetase [9]. In this reaction, 5-methyl tetrahydrofolic acid (5-methyl-FH4) is involved as a methyl group donor (Fig. 1), whereas cobalamin is just intermediate acceptor of the methyl 0091-7435/$ - see front matter D 2004 The Institute For Cancer Prevention and Elsevier Inc. All rights reserved. doi:10.1016/j.ypmed.2004.04.047 M. Wolters et al. / Preventive Medicine 39 (2004) 1256–1266 1257 Fig. 1. Role of cobalamin in homocysteine metabolism (Ref. [30], modified). Abbreviations: SAH: S-adenosylhomocysteine; SAM: S-adenosylmethionine; THF: tetrahydrofolate; 5-CH3-THF: 5-methyl tetrahydrofolic acid; TCC: tricarboxylic acid cycle. group. In cobalamin deficiency, methionine synthesis is impaired and homocysteine can accumulate. Furthermore, the methionine synthetase reaction provides tetrahydrofolic acid (THF), which is the essential form for other folatedependent reactions [10]. Vitamin B12-deficient subjects exhibit losses of this functional form of folate since 5methyl-FH4 is accumulated via the methyl-folate trap. This explains why many symptoms of cobalamin deficiency are similar to folate deficiency. Adenosylcobalamin, which is located in the mitochondrion, is required as a coenzyme for methylmalonyl-CoA mutase. Methylmalonyl-CoA mutase catalyzes the conversion of methylmalonyl-CoA to succinyl-CoA, a metabolite of the citric acid cycle. This is an important biochemical reaction in the degradation of odd-chain length fatty acids and requires first the carboxylation of propionyl-CoA (supplied by the h-oxidation) to methylmalonyl-CoA. Owing to loss of methylmalonyl- CoA mutase activity, vitamin B12-deficient subjects show accumulation of methylmalonic acid. Furthermore, the degradation of the branched-chain amino acids valine and isoleucine leads to methylmalonyl-CoA, which is then rearranged to succinyl-CoA [11]. Cobalamins are exclusively synthesized by bacteria [12]. Rich sources of cobalamin are animal organ meats (especially liver and kidney), fish, mushrooms, eggs, and milk products [13]. Food from plant sources does normally not contain cobalamin, but very small amounts can be found in fermented products or due to bacterial contamination. These traces are not adequate to meet the vitamin B12 requirement. Algae are often advertised as vitamin B12 sources. However, algae contain only ineffective analogs of the vitamin, which in addition are able to inhibit the metabolic functions of the biologically active vitamin. Nor does yeast supply available vitamin B12. Intestinal synthesis of the bacterial flora in 1258 M. Wolters et al. / Preventive Medicine 39 (2004) 1256–1266 humans is not sufficient; thus, dietary cobalamins are required [14]. Diagnosis of vitamin B12 deficiency and status indicators There are various methods for determining inadequate vitamin B12 status. Deficiency of vitamin B12 leads to impaired DNA synthesis and thus to delay or failure of normal cell division, particularly in the erythropoiesis. A reduction in mitotic rate results in macrocytosis (megaloblastic transformation) with an increased mean cellular volume (MCV) of >100 fl. This MCV elevation with or without anemia represents a relatively late sign of a progressed deficiency. It has to be considered that elevated MCV is not a specific marker of vitamin B12 deficiency but is also observed in folic acid deficiency. Vitamin B12 and folate deficiencies are frequently found in hepatic diseases, hemodialysis patients, and alcoholism; hence, elevated MCV in those patients can also be a result of folic acid or vitamin B12 deficiency [15,16]. The determination of the cobalamin concentration in serum or plasma is more specific but varies depending on the method and the particular laboratory. In adults, a concentration of 150 pmol/L (200 pg/mL) is considered the lowest level for an adequate supply. In a developing deficiency, serum concentrations are maintained by depleting stores of the vitamin. Therefore, a concentration above the cutoff of 150 pmol/L does not inevitably reflect a sufficient vitamin B12 status as shown in some studies, indicating that the concentration is not a significant variable [17]. On the other hand, if the cobalamin concentration is below this cutoff, depleted stores can be assumed but are not necessarily present [15,16]. Because of these results, a serum cobalamin cutoff value of <220 pmol/L (<300 pg/mL) has been proposed [18]. Based on studies with the more sensitive indicators of cobalamin status, methylmalonic acid (MMA), and homocysteine (see below), Lindenbaum et al. [19] suggested a cutoff value of 258 pmol/L (350 pg/mL) in elderly subjects. Subjects with low vitamin B12 concentrations exhibited significant elevations of MMA and homocysteine concentrations. In the meanwhile, other authors agree that the cutoff value of 150 pmol/L is too low. For example, in a sample of elderly patients with cobalamin concentrations below this value, 40% of the subjects had increased serum MMA levels. In another study, as many as 80% of the subjects aged 65 years with cobalamin concentrations V148 pmol/L had increased MMA and homocysteine values [18]. Thus, the limit between sufficient and insufficient status is probably between serum cobalamin concentrations of 220 –258 pmol/L [18 –20]. In the case of concentrations below 220 pmol/L, further diagnostic measures are necessary. These early markers of cobalamin deficiency could be elevated plasma homocysteine, elevated serum MMA, and decreased serum holotranscobalamin (holoTC) [21,22]. Elevated homocysteine is an important marker for vitamin B12 and/or folate deficiency and it may also indicate a low vitamin B6 status. In elderly people with normal folate and vitamin B6 status, elevated homocysteine is generally a consequence of cobalamin deficiency [23]. Homocysteine is not a specific variable because it is not possible to differentiate between a vitamin B12 and a folate deficiency. Therefore, additional diagnostic measures such as the MMA or the holoTC concentration are required (see below). Homocysteine concentrations are also elevated in renal insufficiency and hypovolemia [3]. Different levels of total homocysteine in plasma have been suggested as normal: <14 Amol/L [24], 5– 13.6 Amol/L [25], and 4.9– 11.7 Amol/ L [26]. Since results of many studies showed that the prevalence and mortality of cardiovascular disease (CVD) increased if a concentration of 10 Amol/L was exceeded [27,28], this limit has been suggested as desirable [29]. Values of >12– 30 Amol/L are classified as moderate hyperhomocysteinemia [11]. A more specific and sensitive indicator of cobalamin status is the serum methylmalonic acid (MMA) concentration. Elevated MMA is a direct metabolic consequence of vitamin B12 deficiency, as shown in Fig. 1 [30]. Thus, MMA is an important biochemical marker of cobalamin status [3,25,31,32]. The reference range of serum MMA concentrations in healthy adults is 73 – 271 nmol/L [33]. It has to be considered that elevated MMA is also observed in renal insufficiency and hypovolemia [3]. Beside MMA, which is an expensive measure, holotranscobalamin (holoTC) has been suggested to be an early marker of cobalamin deficiency. holoTC contains the biologically active vitamin B12 fraction bound to transcobalamin II (TC II) because TC II promotes the uptake of its vitamin B12 by all cells. Only 6– 20% of total serum cobalamin is present in the active form as holoTC [21,34]. In recent studies, holoTC has been shown to be the most sensitive marker of vitamin B12 deficiency followed by MMA. However, in renal dysfunction, holoTC increases and cannot be used as a marker of cobalamin status [21]. Another indicator for vitamin B12 deficiency is the increased amount of formiminoglutamic acid in the urine following an orally administered dose of histidine. Since formiminoglutamic acid excretion increases in folic acid deficiency as well, this parameter lacks specificity for cobalamin deficiency. In contrast, elevated propionate and 2-methylcitrate concentrations are specific markers of vitamin B12 deficiency because both rise in cobalamin-deficient subjects. However, both methods are not applied frequently in routine laboratories [3,15]. Herbert (1994) suggested four stages of negative cobalamin balance in vitamin B12 deficiency: The first stage is serum depletion indicated by low vitamin B12 on transcobalamin II (i.e., low holoTC) [35]. The second stage is cell depletion, which is also shown by decreased holoTC as well as by low holohaptocorrin and low erythrocyte cobal- M. Wolters et al. / Preventive Medicine 39 (2004) 1256–1266 amin concentrations. The third stage is biochemical deficiency with slowed DNA synthesis, elevated serum homocysteine, and methylmalonic acid concentrations; and finally, the fourth stage is anemia, the clinical deficiency. Late clinical signs of vitamin B12 deficiency are megaloblastic anemia and neuropsychiatric disorders [21,35]. Prevalence of cobalamin deficiency in the elderly In elderly subjects, the prevalence of subnormal cobalamin concentrations varies between 10% and 43% depending on the diagnostic criteria [3,36 – 41]. If the previously considered threshold of 150 pmol/L (200 pg/mL) for a normal vitamin B12 status is used, only 10 –15% of the elderly subjects are classified as cobalamin deficient. Classical deficiency symptoms such as megaloblastic anemia often fail to appear [42]. Today, however, a threshold of 220 – 258 pmol/L (300 – 350 pg/mL) is recognized as a marker for a desirable status in the elderly [4,19,20] or otherwise more sensitive markers such as the blood concentration of homocysteine or methylmalonic acid are used. Then the prevalence of cobalamin deficiency rises to up to 43% [3,4]. As observed in several studies, cobalamin deficiency appears in most cases together with insufficient folate status [24,38,43 –45]. For example, in 66% of the participants of the Framingham study who exhibited low serum folate and elevated homocysteine concentrations, MMA was also increased [41]. We performed a study with healthy women aged 60 –70 years (n = 176) who did not use supplements. Women with serum cobalamin below 258 pmol/L exhibited significantly higher methylmalonic acid concentrations than those with higher serum cobalamin. In total, 9.6% of the women had elevated MMA concentrations [36]. Aetiopathogenesis of cobalamin deficiency There is a variety of reasons for inadequate cobalamin status (Table 1) in the elderly. The main problems are impaired absorption, and thus an increased need of vitamin B12 whereas other reasons like dietary insufficiency are less important. Impaired absorption In elderly subjects, decreased gastric secretion due to type B chronic atrophic gastritis is the major cause of vitamin B12 deficiency [3,46 – 48]. Studies suggest that 20 –50% of elderly people are subject to chronic atrophic gastritis, depending on the definition used [2]. As shown in the Framingham Heart Study, the disease is highly prevalent in very old people. Prevalence of chronic atrophic gastritis in subjects aged 60 – 69 years was 24% and rose to 37% in subjects aged 80 years and over [49]. Similar findings of an 1259 Table 1 Causes of cobalamin deficiency [13,16,21] Dietary deficiency Strict vegetarian diet Poor diet Low intake Malabsorption Pernicious anemia (type A chronic atrophic gastritis) Gastrectomy Type B chronic atrophic gastritis (reduced release of cobalamin from its bound form in food) Zollinger – Ellison syndrome Intestinal diseases, especially of the ileum (celiac disease, Crohn’s disease, ileitis) Resection of the ileum Pancreatic insufficiency Parasitism (broad tapeworm Diphyllobothrium latum) Bacterial overgrowth Antiepileptic agents (carbamazepine, phenytoin, primidone) Proton pump inhibitors (omeprazole) Histamine (H2) receptor antagonists (cimetidine, ranitidine) Antidiabetic drug metformin Antibiotics (chloramphenicol, neomycin) Cholestyramine Increased requirement MTHFR mutation Hyperthyroidism Diabetes mellitus Renal insufficiency Smokers Regular alcohol intake age-dependent development have been found previously [50 –54] and have been confirmed by subsequent studies [55,56]. The main characteristics of chronic atrophic gastritis are reduced gastric secretion of HCl and pepsinogen, in an advanced stage the secretion of intrinsic factor is also diminished [2,3]. These changes have severe consequences for the intestinal release of vitamin B12 from food. As shown by Doscherholmen and Swaim [57] as well as Bradford and Taylor [58], the bioavailability of dietary cobalamin is low in atrophic gastritis. Normally, proteinbound cobalamin is released by gastric acid and proteolytic pepsin and is for the most part subsequently bound to haptocorrins [59]. Cobalamin is liberated by pancreatic proteases in the intestinal lumen and bound to IF, which protects the vitamin from catabolism by intestinal bacteria. This complex associates with cubilin, which initiates Ca2+dependent receptor-mediated endocytosis together with another protein called megalin. Due to the low pH in the endosomes, the release of cobalamin from its IF-B12 receptor complex already starts here and continues in the emerging lysosomes. Afterwards, released cobalamin is bound to transcobalamin II (TC-II) in secretory vesicles. (Fig. 2). Subsequently, cobalamin transcytosis occurs with a 6- to 8h delay [60,61]. In inadequate gastric HCl and pepsinogen secretion, the absorption process is impaired and cobalamin absorption is limited [48]. Furthermore, reduced acid secretion leads to an elevated pH in the small intestine, which weakens the barrier protecting against microorganisms and 1260 M. Wolters et al. / Preventive Medicine 39 (2004) 1256–1266 Fig. 2. Intestinal absorption mechanism of vitamin B12 [61]. elevates small intestinal permeability. Thus, bacteria can pass over from the colon and result in small intestinal bacterial overgrowth, most frequently including Campylobacter, Yersinia, and Clostridium spp. This leads to a competition for uptake of vitamin B12 and further reduces cobalamin availability [62]. The main cause of gastric atrophy is not aging itself, but a chronic Helicobacter pylori infection [3,48]. It is estimated that in the U.S. population, 10% of the subjects aged up to 30 years are infected, while about 60% of the elderly (>60 years) are infected [63]. Helicobacter infection is highly prevalent in subjects with low socioeconomic status [64]. Type A atrophic gastritis (pernicious anemia) is mostly diagnosed in the elderly but is uncommonly the cause of the age-associated cobalamin deficiency [46]. However, in practice, pernicious anemia is often disregarded in the elderly as shown by Carmel [65]. In this study, 1.9% of 729 included subjects (>60 years) exhibited the typical biochemical changes found in pernicious anemia (low cobalamin, abnormal result in Schilling test, presence of antibodies to IF), but the disease had not been previously diagnosed. Chronic atrophic gastritis is characterized by an intensive gastric mucosa atrophy, which is associated with the destruction of the parietal cells. This chronic autoimmune gastritis develops with antibodies to gastric parietal cells (APCA) and leads to an achlorhydric stomach as well as a loss of IF. Thus, cobalamin malabsorption ensues [66]. Changes in gastric physiology can also be induced by several drugs, which consequently impair cobalamin metabolism [67]. Elderly people and especially multimorbid seniors are at risk because they often take different drugs. Absorption of vitamin B12 is predominantly reduced by proton pump inhibitors such as omeprazole and lansoprazole (Table 1). These drugs are used in the treatment of Zollinger – Ellison syndrome, reflux esophagitis, and peptic ulcer. They inhibit gastric acid secretion and reduce the release of cobalamin from food [58,68,69]. In this case of drug –nutrient interaction, only the absorption of protein- bound vitamin B12 is reduced while the absorption of crystalline forms of cobalamin is not impaired. Furthermore, histamine (H2) receptor antagonists such as cimetidine or ranitidine reduce vitamin B12 release from food, but the vitamin status seems to be almost unaffected by these drugs [69]. Other drugs with negative influence on the vitamin B12 absorption are the cholesterol-lowering drug cholestyramine, the antibiotics chloramphenicol and neomycin, and metformin [13,70]. The latter reduces the intestinal availability of free calcium ions, which are required for vitamin B12 absorption. However, the loss of vitamin B12 can be prevented if foods rich in vitamin B12 are consumed together with good calcium sources such as milk and milk products [71]. Dietary insufficiency In contrast to the abovementioned problems, nutritional deficiency of vitamin B12 plays a minor role in reduced cobalamin status. Studies show that the dietary intake of the vitamin from food in the United States exceeded the RDA of 2.4 Ag/day [15]. In Germany, women aged over 60 years consumed 4.8 Ag on average, while the average intake in men was about 5.9 Ag/day [72]. This agrees with our own investigations in 174 women aged 60– 70 years, who had a mean dietary cobalamin intake of 5.1 Ag/day [36]. Therefore, in elderly people, dietary intake of vitamin B12 does not significantly influence the prevalence of cobalamin deficiency. Howard et al. [73] investigated dietary cobalamin intake in elderly subjects with abnormal cobalamin status and concluded that the high frequency of mildly abnormal cobalamin status in the elderly cannot be attributed to poor intake of the vitamin. However, vitamin B12 intake is a problem in strict vegans who avoid meat, eggs, and dairy products. This group develops signs of cobalamin deficiency if the diet is consumed for several years [74 – 77]. Our own investigations confirm these findings. In the German Vegan Study, 26% of the 149 participants ingesting purely vegetarian diets exhibited an insufficient vitamin B12 M. Wolters et al. / Preventive Medicine 39 (2004) 1256–1266 status [78]. Because of long-term storage of vitamin B12 in the liver, deficiency normally only develops after some years of a vegan diet. However, in elderly subjects, deficiency can develop sooner if absorption is impaired because vitamin B12 is continually secreted in the bile and most of it is reabsorbed in healthy individuals. Enterohepatic circulation is important and vitamin B12 losses are much larger in individuals who malabsorb B12 [13]. As shown in a recent study, even lactovegetarians and lacto-ovo-vegetarians exhibit metabolic features indicating vitamin B12 deficiency [77]. Increased requirement of vitamin B12 Cobalamin deficiency in older adults is mostly due to food cobalamin malabsorption. Since older people with low cobalamin and elevated serum MMA mostly do not have true pernicious anemia, they should be able to absorb free or synthetic cobalamin. Screening of MMA, holoTC, and homocysteine concentrations as well as cobalamin, folate, and B6 concentrations in elderly adults indicated that elevated concentrations of the metabolites are related to subnormal vitamin status and decreased renal function. Thus, elderly subjects may require higher circulating B vitamin concentrations to maintain concentrations of MMA and homocysteine within the normal range [79]. Moreover, individuals homozygous for methylenetetrahydrofolate reductase (MTHFR) polymorphism 677 may have increased vitamin B12 and folate requirements [80]. Two studies showed that high supplemental doses of cobalamin are necessary to normalize serum MMA in older people [20,81]. In 23 older cobalamin-deficient subjects, daily intake of 25 or 100 Ag oral cobalamin for a 6-week period was not sufficient to normalize serum MMA in all elderly subjects whereas the concentrations were reduced by 1000 Ag daily. Since in screening studies doses of 30 Ag cobalamin daily decreased prevalence of increased MMA, a longer treatment period might be necessary to normalize serum MMA concentrations. Most elderly subjects with cobalamin deficiency need larger doses than available in usual cobalamin supplements [81]. This is confirmed by a study with oral daily supplementation with 500 Ag cyanocobalamin, 800 Ag folic acid, and 3 mg vitamin B6 for 4 months, which was effective in normalizing plasma homocysteine and serum MMA levels in 70- to 93-year-old community-dwelling subjects [82]. Pathophysiological consequences of vitamin B12 deficiency and hyperhomocysteinemia in the elderly 1261 for congestive heart failure [85]. It is estimated that about 10% of atherosclerotic diseases is related to moderately elevated homocysteine concentrations. A mild elevation of plasma homocysteine can be found in about 5 –7% of the general population [86], whereas 20 – 50% of the subjects with atherosclerotic diseases exhibit a mild homocysteine elevation [87]. However, recent studies have shown contradictory results. In some trials, highly significant associations between cardiovascular diseases and homocysteine concentrations were found whereas in other studies no association could be discovered [88]. A meta-analysis that evaluated the results of 30 studies including 5,073 cases of ischemic heart disease and 1,113 cases with stroke showed that elevated homocysteine levels are a moderate independent predictor for these diseases in healthy populations [88]. After data correction for various confounders such as age, blood pressure, smoking, and cholesterol concentration, it was concluded that a 25% homocysteine reduction (about 3 Amol/L) was associated with 11% risk reduction for ischemic heart disease and with 19% risk reduction for stroke. This result shows that decreasing the mean homocysteine level in the population can significantly reduce important health risks [88]. Another meta-analysis also yields strong evidence that the association between homocysteine and cardiovascular disease is causal. According to this study, lowering homocysteine concentrations by 3 Amol/L would reduce the risk of ischemic heart disease by 16%, deep vein thrombosis by 25%, and stroke by 24% [89]. Furthermore, treatment with homocysteine lowering B vitamins (folic acid, vitamin B12, and vitamin B6) significantly decreases the rate of restenosis and the need for revascularization of the target lesion after coronary angioplasty [90]. Despite this empirical evidence, to date it is not definitely known whether hyperhomocysteinemia is a cause of atherosclerosis or only a result of the disease [5,83]. However, in vitro studies and results of experimental animal studies confirm the hypothesis that homocysteine plays a role in the pathogenesis of atherosclerosis since it initiates various atherogenetic mechanisms [4]. Fig. 3 gives some examples for atherogenic effects of homocysteine [29]. Many clinical studies were able to show that supplementation with vitamin B12 and folic acid efficiently reduces homocysteine concentrations [91]. In most individuals, folic acid is the more effective substance because in the adult population insufficient folic acid status is highly prevalent, whereas vitamin B12 status is generally sufficient in young adults. However, elderly people often exhibit vitamin B12 deficiency; thus, cobalamin supplementation may play a major role in lowering homocysteine in this group. Neuropsychiatric symptoms Atherosclerotic vascular diseases Even moderately elevated homocysteine concentrations are associated with an increased risk for atherosclerotic [83] and thrombotic events [11,84] and seem to be a risk factor Cognitive impairments are often associated with insufficient cobalamin status or elevated homocysteine or methylmalonic acid concentrations [4]. Plasma homocysteine seems to be an important predictor for mental performance 1262 M. Wolters et al. / Preventive Medicine 39 (2004) 1256–1266 Fig. 3. Examples for atherogenic effects of homocysteine [based on data of 29]. [92]. In cognitively normal elderly community dwellers, elevated plasma homocysteine and elevated serum levels of methylcitric acid indicating insufficient cobalamin status had an independent association with cognitive impairment [93,94]. It is estimated that, independent of the intelligence, homocysteine is responsible for 11% of the variance of cognitive performance [95]. Furthermore, vitamin B12 can influence mood as shown in an epidemiological study involving 700 persons aged >65 years. In the group with vitamin B12 deficiency, persons with depression were twice the number than in the group with normal cobalamin values [96]. An association had also been found in a study with 3,884 seniors in the Netherlands. The prevalence of depressive symptoms was associated with vitamin B12 and homocysteine concentration in blood. This association was especially pronounced in hospitalized seniors. In this group, about 30% of all depressive patients were classified as cobalamin deficient [97]. It is assumed that an insufficient vitamin B12 status may also be involved in the pathogenesis and the progression of dementia (e.g., Alzheimer’s dementia). In patients diagnosed with Alzheimer or vascular dementia, elevated homocysteine concentrations were highly prevalent [98 – 103]. This observation is confirmed by the data of the Framingham population, which shows that the risk of developing Alzheimer’s dementia nearly doubles with plasma homocysteine concentrations above 14 Amol/L [104]. In several studies, an inverse correlation between plasma homocysteine concentrations and cognitive performance has been assessed [105 –108]. To date there is a lack of large interventional studies showing a benefit of vitamin B12 supplementation in neurocognitive impairment or dementia [109]. One effect of supplemental vitamin B12, B6, and folate seems to be the improvement of blood –brain barrier function [110]. Since cobalamin metabolism is closely related to folic acid metabolism and deficiency of both vitamins leads to elevated homocysteine concentrations, the effects of both vitamins can hardly be distinguished. Clinical studies evaluating the effect of a combined therapy with folic acid and vitamin B12 have led to contradictory results. In some studies, an improvement of cognitive performance was detected after supplementation with both vitamins [111 – 113], whereas other investigators found no positive results [114 – 116]. Results of a clinical study with high-dose cobalamin supplementation indicated a prominent correlation between duration of cognitive symptoms and response to therapy [117]. It is assumed that for a successful therapy, an early intervention plays a major role [118]. While the exact reasons for the correlations between cobalamin deficiency and cognitive impairments are unknown to date, there are some experimental findings that may explain a relation between the metabolites S-adenosylmethionine (SAM) and homocysteine (Fig. 1). SAM is an important methyl group donator in many neurophysiologically relevant reactions. Decreased SAM values in spinal fluid have been observed in patients with Alzheimer’s dementia and depression [119]. SAM-dependent reactions are the methylation of phospholipids as well as the synthesis of various neurotransmitters (e.g., acetylcholine). The demethylation of SAM leads to S-adenosylhomocysteine (SAH), which is an inhibitor of the SAM-dependent transmethylation reactions [2,8,120]. Therefore, transmethylation reactions require a SAM concentration above the SAH concentration [121]. In the case of insufficient vitamin B12 and folate status, the vitamin-dependent remethylation of homocysteine to methionine is inhibited and as a consequence less M. Wolters et al. / Preventive Medicine 39 (2004) 1256–1266 1263 Fig. 4. Modified food pyramid for people >70 years [122]. methionine is available for SAM synthesis. Thus, cerebral SAM-dependent transmethylation reactions are inhibited and homocysteine increases [121]. The resulting hypomethylation is seen as a responsible factor in various neurological and psychiatric diseases such as dementia and depression [2,8,121]. Furthermore, elevated homocysteine may contribute to the development and progression of vascular dementia due to its involvement in atherosclerosis (see above). Recommendations Because of the problem of insufficient vitamin B12 status in the elderly, many institutions generally recommend supplementation with cobalamin for elderly subjects. For example, the food pyramid based on the Dietary Guidelines for the Americans has been modified for people aged 70 years and over (Fig. 4). In this pyramid for the elderly, daily supplementation with vitamins B12, D, and calcium is recommended, while folate fortified foods should be used (flour has had to be fortified with folic acid in the United States since 1998) [122]. The U.S. Food and Nutrition Board recommends the use of supplements and/or the intake of fortified food (e.g., grain products) for elderly people as well because absorption of crystalline vitamin B12 is not influenced by atrophic gastritis type B [3]. However, studies have shown that the use of supplements or enriched foods reduces the prevalence of cobalamin deficiency in the elderly, but there still remains the risk of deficiency due mostly to low dosages [19,20,123,124]. In a sample of elderly aged 65 – 100 years, 46% indicated regular consumption of cobalamin supplements or enriched foods. Nevertheless, 13% was classified as vitamin B12 deficient because of serum cobalamin concentrations V221 pmol/L and MMA concentrations >271 nmol/L [20]. In the elderly, supplementation with up to 50 Ag/day vitamin B12 seems to be insufficient to avoid poor cobalamin status [20]. Because of the high prevalence of vitamin B12 deficiency and its association with neurocognitive diseases, the daily use of cobalamin supplements of >50 Ag/day can be recommended for elderly people aged 60 years and over. This preventive measure assumes no side effects and would be useful in respect to a risk – benefit analysis. Due to insecure cobalamin supply, it is necessary to monitor the vitamin B12 status regularly in elderly subjects (z60 years). Since serum vitamin B12 is no reliable marker of subclinical cobalamin deficiency, measurement of more sensitive markers like MMA and holoTC should be considered. 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