Motives to follow this diet are mostly related to animal welfare and ethics, yet ecological and health-oriented reasons also play a role for many [2,3].
Recent surveys from Western nations suggest that typically between 1% and 5% of the population are currently following a vegan diet , , , , and that this diet is particularly popular in people aged between 15 and 34 years .
As this overlaps with many women’s child-bearing years, there are health concerns about the coverage of essential nutrients, and consequently, there is an urgent need for research in this area.
There are several official guidelines on vegan diets for pregnant women and children, including for paediatricians in Switzerland . Most of these discourage or do not actively recommend a strictly vegan diet for these vulnerable populations, for fear of nutrient deficiencies.
Others, including the British National Health Service, state that a well-balanced diet supplemented with critical nutrients, such as vitamin B12 and D, makes a vegan diet an appropriate option for pregnant women and children .
A recent Swiss study showed that despite substantial differences in micronutrient intake and deficiencies between omnivores, vegetarians and vegan adults, all 3 types of diet can potentially fulfil micronutrient requirements . To date, only a few studies have investigated the impact of a vegan diet on the health and growth of vegan children.
A recent German study compared omnivorous, vegetarian, and vegan children, and showed no significant differences in macronutrient intake or growth . Nevertheless, more and larger studies, as well as reviews specifically on vegan children, are needed to assess the effect of a vegan diet on the health and growth of children and adolescents.
We identified crucial nutrients for the nutrition of vegan children, summarised the available evidence of their sources, the epidemiology of deficiencies, and investigated the effects on overall growth in such children.
As there have been major shifts in the demographic make-up of the vegan population with distinct subgroups, special attention was given to account for these differences. We aimed to summarise the state of what is currently known and what aspects should be included in future research to fill the existing gaps.
To date, there have been a limited number of studies on the impact of a vegan diet on children’s health and growth. Consequently, we limited our results to particular outcomes and complemented the results with data on vegetarian children and vegan adults.
In adults, vegan diets have been shown to offer significant health benefits when compared to standard Western diets, such as a reduced risk for ischemic heart disease, type 2 diabetes, hypertension, certain types of cancer, and obesity. The main reasons for this are the low intake of saturated fats and high intake of whole grains, vegetables, fruits, nuts, and seeds, many of which are rich in fibres and phytochemicals, which leads to lower total and LDL cholesterol and improved serum glucose control [20,59].
Furthermore, psychosocial factors have a significant influence on health and must be carefully assessed as potential confounders in population-based studies. This is particularly true within the heterogeneous vegan population, where there are subgroups that are opposed to laboratory testing, supplementation with micronutrients, or pharmaceutical medicine (antibiotics, vaccinations, chemotherapy). Chemophobia is a term used to describe this behavior . This trait can markedly influence the appropriateness of the vegan diet.
Not only do sub-groups play a role in the vegan population, but they also have generational effects, as veganism has increasingly become a mainstream phenomenon. There is reason to assume that current vegans may be planning their diets more adequately than vegans did in the past, as there has been a rapid adoption of vegan diets in the general population, beyond the religious, spiritual or naturalist fringe groups of the 20th century, who were often ignorant of or outright opposed to sound nutritional guidance. Web searches containing the word ’vegan’ (https://www.google.com/trends/) suggest a considerable increase in the interest in veganism in most industrialized countries since around 2011.
The search volume has increased by a factor of 5 in the United States and 15‒25 in Western European countries between 2011 and 2020 (Fig. 1). This trend seems to correspond closely to the adoption of veganism, as the number of vegan adults in Germany increased from 0.1% to 1% of the population between 2007 and 2014 .
One example of how mindset can influence the appropriateness of a vegan diet is the parents’ use of cobalamin supplementation in their children’s diets. A longitudinal study published in 1988 stated that ’most’ vegan parents were aware of the importance of cobalamin substitution . Furthermore, most of their children had sufficient intake of cobalamin (mean 280% of the recommended daily amount; range 20‒1695%) .
In 1989, a study on a community called The Farm showed that of 404 children, 75% were on a vegan diet. Of the entire population, 76% used vitamin/mineral supplementation, which was added to their self-made plant milk, and 78% used nutritional yeast (erroneously believed to contain cobalamin naturally) [24,56].
Preliminary results of the German VeChi Youth study, comparing 114 vegan to 150 vegetarian and 137 omnivorous children and adolescents, aged 6‒18 years, showed no significant differences in micronutrient intake between the 3 groups. In all groups, the intake of most micronutrients was sufficient, particularly that of cobalamin, which was supplemented in 88% of vegan children and 39% of vegetarian children .
Considering adults from recent studies, it can be assumed that today, 1/3 to 1/2 of all vegans use supplements [9,28,36,62]. Typically, these numbers do not incorporate the use of fortified foods or drinks.
Endogenous biosynthesis cannot be considered to be a trusted method of securing cobalamin supply, particularly for vegan risk sub-populations, such as pregnant women or children. However, it cannot be ruled out that, for a few individuals, it is possible to produce sufficient amounts of cobalamin via microbiome, as there are studies where cobalamin supplementation played no or only a small role in explaining cobalamin status [9,48].
In 1 study focusing on raw vegans who did not take supplements, the duration of the vegan diet did not negatively correlate with cobalamin status, suggesting that as much as 24% of participants could sustain sufficient levels of cobalamin despite using no supplementation .
Further research is needed to clarify this issue. Nevertheless, these results and possible real-life exceptions can be detrimental to the efforts of convincing vegans to initiate and adhere to cobalamin supplementation. This is aggravated by a delay in deficiency due to internal cobalamin stores , which can further promote the denial of the need for cobalamin supplementation in vegans.
The way that nutritionists and health care providers respond to vegan parents is also important. A recent Italian survey showed that 77.4% of vegetarian and vegan parents met opposition from their pediatricians, and 45.2% of them found that their pediatricians were unable to provide adequate nutritional information during the weaning period .
A more open and informed approach might avoid driving these parents away from proper care but given the current state of research on the topic, a cautious approach is justified.
The data suggest that vegans may have physiologically lower ferritin levels, but no increased risk of iron-deficiency anaemia.
Several mechanisms could account for this finding. It is known that plant-based, non-haem iron has inferior bioavailability . Recent discoveries show that plant ferritin, which is abundantly present in legumes, including soybeans, contains a significant amount of iron that is released during digestion or is absorbed partly or entirely through endocytosis in the small intestine [65,66].
Vegan and vegetarian diets are generally high in vitamin C , which enhances iron absorption, but is also high in phytates, polyphenols, and fibre [28,67], which inhibit iron absorption. Furthermore, the body can adapt to low iron intake over time by reducing iron losses , and can also adapt to using iron of low bioavailability, with an increase in absorption of almost 40% over a period of 10 weeks . Lastly, iron uptake of both haem and non-haem iron can increase 10-fold when the body is in a state of iron deficiency .
While Ca is often thought to inhibit iron absorption, observational studies comparing whole diets seem to suggest adaptation to the inhibitory effect, and intervention studies have shown that Ca supplementation as high as 1200 mg/day does not affect iron status .
Comparing vegetarian and vegan diets, 1 study found that proteins present in milk, such as whey and casein, inhibit iron absorption , yet a recent summary of observational studies on dairy products and iron status showed conflicting results .
The comprehensive EPIC-Oxford study  found that, in 1126 adult vegans, 44.5% did not meet a Ca intake of 525 mg/day and therefore, they had a 30% increased risk of bone fractures.
In this study, lifestyle parameters that are typically protective in vegans and have a high impact on bone health, such as BMI, physical activity , alcohol consumption, and smoking, were factored out [22,73,74]. Unadjusted data were provided by a 2009 meta-analysis , which found that, while vegetarian and particularly vegan diets were associated with a lower bone mass density (BMD), the magnitude of the effect was deemed likely to be clinically insignificant by the authors, indicating that there was no increased fracture risk.
Vegetarians scored 2% lower (95% CI: 1%‒4%) while vegans scored 6% lower (95% CI: 2%‒9%) on BMD when compared to omnivores . A more recent meta-analysis  reported an even lower BMD and increased bone fracture rates in vegans. However, these authors misclassified 2 of the 4 study populations (Fontana et al., 2005) as vegan when they were in fact raw vegetarians.
The third study showed no statistically significant differences in BMD in young omnivores, vegetarians, and vegans, and a fourth study was the previously discussed 2009 meta-analysis that claimed statistically significant, yet clinically insignificant results .
Despite a wealth of investigations, it remains controversial whether higher Ca intake or Ca supplementation is associated with better BMD , , , . For example, a 2006 meta-analysis of 19 studies and 2859 children concluded that Ca supplementation did not increase BMD regardless of sex, baseline Ca intake, pubertal stage, ethnicity, or level of physical activity .
A 2005 review examining the impact of dairy products on bone health in child and adolescent bone mineralisation found scant evidence for beneficial effects . Yet, Ca-deficiency during childhood may affect peak bone mass, most of which is accumulated at the age of 18 years, and which predicts fractures in old age .
In an intervention trial, the effect of milk supplementation on total-body bone mineral acquisition in adolescent girls was evaluated. The intervention group that received 1 pint/day of milk (whole or reduced fat) for 18 months had a significantly greater increase in BMD, bone mineral content (BMC), and significantly higher concentrations of serum IGF-1 than the control group .
Another study concluded that there was only a weak connection between Ca intake and bone health, and that other factors play more dominant roles . For example, Ca absorption is reduced by approximately 66% when an individual is deficient in vitamin D .
Vegan children are generally lighter but are not underweight. This can be considered favourable, as childhood obesity is a growing problem in many industrialised nations . Current evidence shows that there are no significant differences in average height. However, there is evidence that a low percentage of vegan children may be unusually small .
This could be caused by nutritionally inadequate vegan diets. It is also possible that milk, through stimulation of the IGF-1 axis, stimulates longitudinal growth in children and adolescents [84,85]. Data on the height of life-long vegan adults would help to clarify this issue, but no such data have been published to date.
IGF-1 can also exert anabolic effects on bone mass during adulthood reaching a maximum around the age of 15 years . In lactose-intolerant children who avoided milk, no differences in bone mass were found relative to the general population, yet a milk-free diet increased the likelihood of fractures by 1%‒4% overall, an effect that was, however, only significant in girls when comparing genders .
There are a number of methodological problems in existing studies on vegan nutrition that should be taken into consideration in further scientific inquiries. Usually, supplement use or use of fortified food and drinks is not assessed; therefore, nutrient intakes of vegans tend to be underestimated.
Similarly, both ferritin as a source of iron and the use of iron cookware are rarely considered, leading to an underestimation of total iron intake. Finally, the endogenous synthesis of cobalamin must be further explored. For these reasons, nutrient plasma status should be preferred over estimated nutrient intake whenever possible.
When including younger children, urinary sampling could be a more suitable method of assessment than blood sampling, such as using urine methylmalonic acid (MMA) assays when determining cobalamin levels . Future research should also account for demographic shifts within the vegan population, giving more weight to data assessed after 2011 to maximise external validity, and to discriminate between vegan sub-populations that are open or closed towards scientific approaches, towards health in general, and toward supplementation. Studies should always assess the modes and dosages of supplementation, the consumption of fortified foods and drinks, and adherence to the diet itself.
Plant-based dietary quality and depressive symptoms
Dietary intervention studies highlight healthy dietary patterns rich in fresh fruits, vegetables, nuts, seeds, whole grains and legumes as promising in reducing symptoms of depression.4 20 However, the evidence of the association between plant-based dietary patterns and depression is inconsistent and conflicting.21
Some studies suggest that plant-based diets (PBD) are associated with improved mood and mental health.22 Others suggest that PBDs are associated with a greater risk of depressive symptoms,23 24 while others find no relationship.25–27 A meta-analysis of 13 studies by Iguacel et al 28 found that vegans and vegetarians were at increased risk of depression (OR=2.14, 95% CI: 1.11 to 4.15).
Another systematic review and meta-analysis of ten observational studies by Askari et al 29 found no association between those who consumed a vegetarian diet and depression symptoms (pooled effect size: 1.02, 95% CI: 0.84 to 1.25).
While a narrative review of 19 studies by Jain et al.30 found conflicting information, some studies suggesting that those who adhered to vegan and vegetarian dietary patterns had higher depression rates, while others indicated they were associated with decreased depressive symptoms.
Other primary research studies suggest that young adult vegetarians are at higher risk of depression31 and suicide32 than omnivores in the same age group. The reasons for these conflicting findings are not yet fully understood but may be due to the lack of heterogeneity of the measurement of dietary patterns (self-report), and that quality rather than dietary patterns needs to be further explored in this population.33
Indeed a recent meta-analysis showed an increased risk of depression in vegetarians,34 however, the interpretation of the findings is limited due to the lack of methodological clarity in vegetarian diets being of ‘low’ or ‘no’ meat consumption. As such, diet quality measures in PBD is critical for exploring the association between diet and mental health.
reference link : https://nutrition.bmj.com/content/early/2021/10/28/bmjnph-2021-000332
reference link :https://www.sciencedirect.com/science/article/pii/S0271531721000191?via%3Dihub