1. Introduction
Veganism is defined as a philosophy and way of living, which seeks to exclude, as far as possible and practicable, all forms of exploitation of, and cruelty to, animals for food, clothing and any other purpose [
1]. While a vegan diet is traditionally followed in different parts of India, veganism gained some attention as an alternative ethical movement in Western countries in the 1960s. Recent surveys indicate that the number of self-identified vegans in the USA increased from 0.4% in 2015 to 6% in 2017 [
2]. In the Czech Republic, 1% of the population reported to be vegetarian in 2002, and about 2% in 2003 [
3]. According to a current marketing survey performed in 2019, 1% of Czech population consider themselves as vegans (excluding all animal products) and 3% as vegetarians (excluding only meat). However, in younger adults (18–34 years) the proportion of vegetarians and vegans is 10% [
4].
Based on the concept of the so-called rational vegan diet, promoted by vegan organizations and by some scientific societies, meat and meat products, dairy, eggs and honey can be replaced by legumes and grains as the main sources of protein and nutrients. A rational vegan diet should theoretically meet all of the requirements for nutrients except of cobalamin, which should be supplemented [
5,
6]. However, this approach may not be accepted by some members of the vegan community, and according to a systemic review from 2014 the prevalence rates of cobalamin deficiency in vegetarian and vegan adults and elderly range from 0% to 86.5%, with higher prevalence rates among vegans [
7]. For example, 78% of Slovak vegans show laboratory signs of cobalamin deficiency based on the measurement of cobalamin levels in blood, according to one of the studies included in the review [
8]. Beyond cobalamin supply, there is an ongoing discussion as to whether intakes of plant-derived iron, zinc, protein and total energy are sufficient among vegans, especially in areas such as post communistic Europe, where vegetarian and vegan diets do not have a long-term tradition as in Western European countries. At the same time, there is a lack of resources in the public health sector to address specific healthcare needs of vegans, arising from distinct nutrient patterns of the vegan diet in comparison to traditional western diet. As not much is known about the health status of vegans in the Czech Republic, we aimed to 1/assess cobalamin, and iron status and a risk of associated anemias among vegans and to 2/relate cobalamin deficiency to supplement use and duration of an exclusive vegan diet.
4. Discussion
In the current study involving 151 Czech vegans and 85 non-vegan controls, we showed that vegans have significantly lower levels of cobalamin, hemoglobin and ferritin, but higher folate and MCV. The risk of laboratory signs of cobalamin deficiency among vegans was strongly related to the non-use of dietary supplements, and even irregular users of supplements were at higher risk for low levels of cobalamin and holotranscobalamin compared with regular users or non-vegans. By contrast, our study does not indicate that the duration of adherence to the vegan diet alone is related to the risk of cobalamin deficiency. Despite lower ferritin values among vegans (not related to the duration of vegan diet), the overall presence of the typical laboratory markers of iron deficiency anemia was low in both among vegans and non-vegans, and there were no statistically significant differences in the prevalence of such signs. Ferritin and hemoglobin values were significantly lower among vegan vs. non-vegan men, while no such difference was observed among women.
While evidence from the past years on homocysteine as a biomarker of cardiovascular disease risk is not consistent [
12,
13], our data do indicate that it may be one potential marker of suboptimal cobalamin supplementation among vegans. However, it should be noted that several vegan participants (n = 30) of our study, who were cobalamin sufficient according to their cobalamin levels (cobalamin > 190 ng/L), would have been classified as cobalamin deficient according to their homocysteine (homocysteine > 15 µmol/L, while folate > 4.6 µg/L). Despite the fact, that vegan study participants had a significantly higher risk of lower cobalamin levels overall compared to non-vegans, there was no such difference in homocysteine levels.
The observed tendency for higher MCV values among vegans was no longer statistically significant after adjustment for supplement use. Also, almost all of the participants in the study were in the normal range of MCV, despite having low cobalamin or showing a tendency for lower ferritin. Based on this finding, we assume that MCV may not be a valid marker for cobalamin or iron deficiency anemias in vegans, even though it is traditionally recommended for this purpose. Possibly, our observation can be either explained by higher levels of folate in vegans (masking the underlying cobalamin deficiency) or by lower ferritin levels (as a result of combination of cobalamin and borderline iron deficiency).
While the duration of adherence to the vegan diet was not associated with cobalamin, holotranscobalamin or homocysteine levels in our study, we observed a trend towards decreased iron load and storage with a longer vegan diet duration, ferritin being significantly lower in vegans than in non-vegans (not related to the duration of the vegan diet). Interestingly, many vegans in our study showed iron status parameters that clustered around the threshold value for iron deficiency, but only a minority of them had levels indicating iron deficiency. Although such borderline values could be interpreted as a risk factor for sideropenic anemia, low iron stores were also suggested to be partially responsible beneficial health effects of a vegan diet [
14,
15]. Higher iron load, as primarily reflected by higher ferritin values, is associated with cardiovascular disease and diabetes, and suspected to also be a risk factor for cancer development [
16,
17,
18]. The interpretation of all other iron markers is complicated by their high intra-individual fluctuation, especially among females, that suggests that single examination may not be sufficient to assess iron status.
Given the increasing prevalence of alternative diets, guidelines for cobalamin deficiency assessment by blood markers according to which health professionals can be trained are needed. In this regard, it would have been of interest to evaluate other reliable markers of cobalamin deficiency used in practice, namely methylmalonic acid MMA [
19,
20] in our study population. Unfortunately, however, MMA has not been available in regular clinical practice in the Czech Republic. Though the absence of MMA limits our results, it of note that most general practitioners usually rely on the assessment of cobalamin only, often in combination with MCV, which may not reflect cobalamin deficiency in an accurate manner. Possibly, cobalamin assessments can serve as first line screening tool, with additional holotranscobalamin or MMA measurements in specialized laboratories in case of levels in the lower normal range.
Further limitations of the present study have to be considered. First, our vegan study population was a convenience sample of adults, who voluntarily attended healthcare checkups at the outpatient department of Clinical Nutrition. It is conceivable that this sample may have a higher degree of health consciousness together with greater trust in Western medicine and practicing physicians compared to other Czech vegans, who may be more prone to utilizing alternative medicine. Thus, it can be speculated that the overall prevalence of cobalamin deficiency among vegan adults in the Czech Republic may be higher than in the current sample of vegans. Our study did not include children, pregnant females, or lactating females, who may be particularly vulnerable to consequences of cobalamin deficiency. Indeed, borderline cobalamin status in pregnant women can be associated with increased risk of acquired newborn B12 deficiency and cobalamin alone may not be sufficient to diagnose deficiency among them, which is why MMA tests are required [
21]. Future studies are needed to assess the prevalence and determinants of deficiencies in the mentioned vulnerable groups. As we relied on medical reports, only limited data was available concerning cobalamin supplementation, and we did not have information on the exact doses of supplemented cobalamin, limiting dose-response analyses. Of note, even in the group of long-term vegans without supplement use, there was one person reporting being vegan for 16 years with a cobalamin level 359 ng/L and a homocysteine level of 14 µmol/L. In addition, three other long-term vegans not using supplements had cobalamin values over 190 ng/L, suggesting, there could be an alternative source of cobalamin beyond classical supplements. However, this notion remains speculative, as supplement use was self-reported, and we were not able to further investigate other potential sources of cobalamin.
Our data may stimulate future research, and foster a more evidence-based debate about medical guidelines and recommendations targeting populations with alternative lifestyles in eastern European countries. There is clear indirect evidence that the popularity of alternative diets is increasing even in regions, in which the traditional cuisine is heavily based on animal products and where the availability of plant-based alternatives is not as high as in countries with a longer tradition of veganism. While we showed there is a substantial proportion of vegans, who do not supplement B12 sufficiently, the current shift in eating habits towards plant-based diets is not reflected by current public health recommendations and guidelines.
