There is growing interest in the potential for folic acid fortification in the Americas and recognition of the high prevalence of low plasma vitamin B12 concentrations reported in various studies. This review summarized available data on plasma vitamin B12 and folate concentrations in the Americas. At least 40% of individuals had deficient or marginal plasma vitamin B12 concentrations in almost all locations and across age groups. Low plasma folate concentrations were less common. It is hypothesized that vitamin B12 deficiency may result from a low intake of animal source foods, while a higher intake of refined flour may result in low plasma folate.
Key words: folate, vitamin B12, Latin America
© 2004 International Life Sciences Institute
It is generally assumed that, due to efficient enterohepatic recycling of the vitamin, B12 deficiency is unlikely to occur except in special circumstances. These include long-term consumption of a diet that is strictly vegetarian, pernicious anemia, malabsorption syndromes including tropical sprue and bacterial overgrowth, and other clinical conditions in which the function of the ileum (where vitamin B12 absorption occurs) is impaired. In the past decade we have also become aware that vitamin B12 deficiency occurs commonly in the elderly-even in industrialized countries-due to gastric atrophy.
Our assumption that there is a low prevalence of vitamin B12 deficiency during childhood through adult years needs to be re-examined. Since we discovered a consistently high prevalence of low plasma vitamin B12 concentrations in rural Mexico and peri-urban Guatemala City during the past decade, in adults as well as infants and children, we have become interested in understanding the causes and consequences of this deficiency. Thus this opportunity to review the existing data on the prevalence of vitamin B12 deficiency in The Americas is very relevant to this objective.
Because plasma folate is typically measured in the same assay as plasma vitamin B12, our laboratory has made simultaneous measures of plasma vitamin B12 and folate in Guatemala, Mexico, and other countries. In recent years, countries have obtained data on folate status because of their interest in the prevention of neural tube defects by folic acid fortification of the food supply. In some cases, vitamin B12 was analyzed in the same samples.
The prevalence data presented here were obtained by searching Index Medicus since 1980 for the terms "vitamin B12," "cobalamin," "folate," and "folic acid," and asking PAHO and other contacts for names of investigators who might have relevant data. Data were only collected after 1980 because of doubts about the validity of some of the earlier assay methods for vitamin B12.
A major problem when comparing prevalence of low levels across studies is the variability of cut-offs used to denote deficiency. Thus, in some cases we asked investigators to recalculate their prevalence data based on our proposed cut-points. These were
The data are presented and discussed at the country level, first for vitamin B,2 and then for folate in each case. Except in the case of the Mexican National Nutrition Survey, few of the data were obtained from nationally representative samples, so the characteristics of each sample population are described briefly when available.
Our own research on vitamin B12 deficiency was stimulated by the observation that erythrocyte mean cell volumes in blood samples from a poor region of rural Mexico, 170 km northwest of Mexico City, tended to be large, although not actually macrocytic. We had assumed that the probable cause of the large erythrocytes was folate deficiency, possibly aggravated in adults by consumption of pulque, a local alcoholic beverage. Surprisingly however, we found a high prevalence of low serum vitamin B12 concentrations, but no low serum folate values.2 The prevalence of deficient and marginal plasma B12 values respectively was 41% and 16% in preschoolers (ages 18-36 months), 22% and 25% in schoolers (7-10 years), 19% and 19% in non-pregnant women, 19% and 43% in pregnant women, 30% and 25% in lactating women, and 27% and 15% in adult men. The cut-point for vitamin B12 deficiency was
In a subsequent study designed to assess the benefits of iron and/or zinc supplements on preschoolers in the same communities, we again measured plasma vitamin B12, holoTC II, and folate. A total of 219 children was enrolled, almost all of those between 18 and 36 months of age in the communities.4 Plasma samples were analyzed at baseline and 6 and 12 months later. The prevalence of marginal and deficient plasma B12 concentrations, respectively, was eight and 33% at baseline , three and 22% six months later, and seven and 29% twelve months after baseline. Low holoTC II concentrations averaged 18-40% across the periods. The intra-individual correlation in plasma B12 across periods was strong; r = 0.58-0.73 (P
Oral supplemental vitamin B12, 1 mg, three times a week, for three months, was provided to 128 preschoolers, ages 18 to 36 months, during another study in the same communities (Alien et al., unpublished). The children were part of a multiple micronutrient intervention trial, and all were selected for having low hemoglobin concentrations (80 g/L to 1000 pg/mL at baseline, there was a substantial increase in plasma levels of the vitamin after supplementation. No children had low plasma concentrations of the vitamin after supplementation. In spite of a high prevalence of elevated MCV and MCH levels at baseline, vitamin B12 supplementation did not significantly affect these values. Only 2% of these children had a plasma folate concentration
The Mexico National Survey
Mexico is the only country in Latin America that has assessed folate and vitamin B12 status in a probabilistic sample of the population.5 The 1999 National Survey of Nutrition included measures of "total blood folate." Dried blood spots were collected on filter paper, the folate later extracted and assayed with Lactobacillus caseii. It was then assumed that all the folate was in erythrocytes so that this value could be entered in a regression equation to estimate total blood folate. While this value is more difficult to interpret, the prevalence of low (
In conclusion, the data from Mexico indicate a very high prevalence of vitamin B12 deficiency in all age and physiological status groups, but a lower prevalence of low serum folate.
We have also conducted several studies of the prevalence and consequences of vitamin B12 and folate deficiency in low-income districts of peri-urban Guatemala City. The first study was conducted in a group of school-aged children, all of whom were selected on the basis of having Giardia (unpublished data). The 109 children were aged 6-12 years. Of this group, 13% had a deficient plasma vitamin B12 concentration at baseline, and an additional 34% had a marginal value. None of the children had low plasma folate, only 7% had iron deficiency and 10% had anemia. The second study explored the prevalence of vitamin B12 deficiency in lactating women, and the association between maternal vitamin B12 status, human milk concentrations of the vitamin, and the vitamin B12 status of the infants.6 Participants were 113 women and their infants at 3 months of lactation. Plasma vitamin B12 was deficient or marginal in 47% of the mothers, and concentrations in breast milk were low in 31%. Urinary MMA was elevated in 12% of the infants, and inversely correlated with levels of vitamin B12 in breast milk (r = -0.22). Plasma folate levels were low in 9% of the mothers.
In a third Guatemalan study, plasma vitamin B12 and folate were measured in 128 infants aged 7 to 12 months, from a similar poor, peri-urban location in Guatemala City.7 All of these infants were at least partially breastfed (at least three times per day) and
In the same school district as the first study, the prevalence, predictors and consequences of vitamin B12 deficiency were investigated in schoolers. Children aged 8-12 years were screened to identify 60 children with plasma vitamin B12 levels indicating deficiency, then these were matched by age, gender and school grade with similar numbers of children who had marginal and normal plasma B12 concentrations (final n = 180). Of the total of 554 children screened, 11% had deficient levels of plasma B12 and 22% had marginal values.8 Mean plasma B12 concentrations fell with age across the age period. No child had serum folate
In this Guatemalan study predictors of the children's vitamin B12 status were evaluated.9 The prevalence of Helicobacter pylori and bacterial overgrowth was not different across the B12 status groups. However, there was a significant positive correlation between serum MMA and serum gastrin suggesting that gastric inflammation due to Helicobacter pylori may play some role. The average daily intake of dietary vitamin B12 was 5.5 ± 5.2 ug/day, but 23% had intakes
Evaluation of the neurobehavioral function of the schoolers across the three vitamin B12 status groups revealed that lower plasma vitamin B12 predicted slower reaction times on perception and memory tasks, and less accurate reasoning.10 There were no differences in motor skills or attention. In multiple regression models, both MMA and Hey predicted the same functional deficits as low plasma B12. Academic performance, and interest in working and learning, were negatively associated with plasma MMA, but not Hey.11
In conclusion, there are no representative data for Guatemala. In the peri-urban region of Guatemala City, the prevalence of vitamin B12 deficiency in women, infants and children is very high, while almost no cases of low plasma folate were reported across the five studies. The strongest predictor of low plasma B12 in schoolers was their dietary intake of the vitamin. Low plasma and breast milk vitamin B12 concentrations in the group of lactating women may explain the fact that the majority of infants aged 7 to 12 months in a later study were deficient in the vitamin.
Data on serum folate concentrations (but not on serum vitamin B12) are available from the 1996 National Survey, and are described in more detail by Tacsan et al. elsewhere in this symposium. The Costa Rican data, using a representative national sample, are expressed in terms of severe (45 nmol/L) serum folate concentrations. In nonpregnant, nonlactating women of fertile age the prevalence of these values was 4, 11, 68, and 8%, respectively, and in children
One study of serum vitamin B12 and folate concentrations was conducted in Cuba, two years after the neuropathy epidemic of 1993.12 Volunteers were 141 healthy middle-aged men (mean age 39 y) from health centers in Havana, who gave blood samples every three months for one year. The prevalence of deficient plasma vitamin B12 values ranged from 52 to 82% across seasons, and the prevalence of marginal values ranged from 13 to 36%. Folate status of these men was also poor; 64% to 89% had low serum folate across the seasons, and about one third consumed less than 133 ug/day.
Chile collected information on serum folate as part of their assessment of the impact of folic acid fortification of wheat flour, which started in 2000. More information on the impact of the fortification is provided by Hertrampf elsewhere in this symposium. Prior to folate fortification there was a very high prevalence of both folate and vitamin B12 deficiency. Low serum folate was found in 25%, and low erythrocyte folate, in 65%. In the 598 women studied, serum vitamin B12 was
In a smaller study of free-living, low-middle socioeconomic status, elderly Chileans recruited from an outpatient clinic in Santiago, serum folate and vitamin B12 were also measured.13 The 93 men and 181 women had a mean age of 70.1 ± 6.7 y (range 60-89 y). The prevalence of low serum folate was 33% in women and 50% in men. Serum vitamin B12
A recent study of serum folate in Chilean elderly was conducted to evaluate the effect of flour fortification with folic acid.14 A total of 208 people were recruited from public outpatient clinics in Santiago. Serum folate, B12, and homocysteine were assessed at baseline and six months later. At baseline, vitamin B12 deficiency (in this study, 14 umol/L) in 31%. Six months later serum folate had increased from 16.2 ± 6.2 nmol/L at baseline to 32.7 ± 7.1 nmol/L (P
Based on the prevalence data described above and summarized in Figure 1, the following conclusions can be drawn:
1. There is a high prevalence of vitamin B12 deficiency (at least 40%) in all populations studied. This deficiency affected individuals from infancy through adult years. It is expected to be even more prevalent in the elderly but there are few data on this age group in Latin America.
2. Vitamin B12 concentrations in breast milk were low in rural Mexican and peri-urban Guatemalan women. This suggests that women and their infants may be at particularly high risk of deficiency, and its potential consequences, during the perinatal period.
3. The extraordinarily high prevalence of vitamin B12 deficiency implies that the vitamin be added as a fortificant to dietary staples. This may be especially important if folic acid is used as a fortificant.1
4. The prevalence of low plasma folate concentrations is highly variable. Folate deficiency does not seem to be a serious problem in Mexico, Guatemala, or Costa Rica. The highest prevalence of low serum folate was found in Cuban men and Chilean women.
5. Possible reasons for these differences in nutritional status among populations include variability in vitamin B12 intake from animal source foods, especially meats, and variability in folate intake from legumes (high in folate) vs. refined cereals such as white wheat flour (low in folate).
6. It remains to be determined whether there are any functional consequences of vitamin B12 deficiency in these populations.
Summary of Discussion of Article by Allen
Underestimated prevalence of folate insufficiency. In terms of the folate problem, it was pointed out that one of the consequences of vitamin B12 deficiency could be high serum folate (normal to 2-3 times as high). Particularly in the presence of vitamin B12 deficiency, the data on serum folate might be misleading. They might be artificially high because of the methyl folate, which is trapped in the cell and not converted to polyglutamate, and therefore exits the cell. RBC folate measurement was suggested as a better marker to determine folate status. This difference was noted in the Framingham study and the NHANES, among others. One of the functional indicators of vitamin B12 status is actually low RBC folate in the presence of normal serum folate, which determines vitamin B12 deficiency. Thus, looking at serum folate is insufficient to determine folate status. second, there is a problem with the folate assay. There are two major methods for measuring folate-the microbial assay and another related to the radioassay. The radioassay has been consistently determining folate levels at about 30% less than the microbial assay, so the method used must be known when folate measurements are being compared. Also, the elderly have higher serum folate, so in comparing two populations, there is a physiological reason for the difference. In relation to the bioavailability of vitamin B12 food sources, meat was shown to be inferior to other foods, such as milk. Vitamin B12 intake may not be a sufficient explanation for deficiency.
A literature review did not find higher levels of folate in the order of 2-3 times in the presence of vitamin B12 deficiency. The difference was not found to be that much. Nevertheless, there is less confidence in the folate data presented than in the vitamin B12 data. The main objective of this article was to demonstrate that there is a vitamin B12 problem.
Mexican data on folate status. A question was raised about whether the higher pre-fortification folate levels in Mexico could have been caused by fortified products leaking in from the U.S. This was not considered to be likely, since there is very little exchange of flours between the countries, and wheat flour is more often exported from Mexico to the U.S. rather than the other way around. The communities in Mexico are also mainly maize-eating with low intake of wheat flour.
Guatemalan data on vitamin B12, intake. In the data on dietary intake of vitamin B12, Guatemala was shown to be consuming 4-6 µg/day, which is 2-3 times the RDA for adults in the U.S. An explanation for the discrepancy from the vitamin B12 deficiency picture was requested. Consumption of foods high in vitamin B12, such as liver, at the time of intake data collection was explained as having had suddenly pushed up the average. However, this is not a true reflection of how much vitamin B12 is actually being absorbed; only 1% was suggested as being absorbed from a source like liver. The intake data may be artificially inflated, so it is not sufficient to determine the situation based on diet alone.
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14. Hirsch S, de la Maza P, Barrera G, Gattas V, Petermann M, Bunout D. The Chilean flour folic acid fortification program reduces serum homocysteine levels and masks vitamin B-12 deficiency in elderly people. J Nutr. 2002;132:289-291.
Lindsay H. Allen, Ph.D.
Dr. Allen is with the Western Human Nutrition Research Center and Program in International Nutrition, University of California, Davis, CA 95616.
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