Vegan diet puts people at risk of vitamin B12 and other deficiencies

Maximilian Storz challenges us to “seriously consider to recommend a plant-based diet to all our patients” to mitigate climate change. Moreover, he insists that in a mere sentence we can mention the benefits of plant-based diets or at least a meatless day.¹

I beg to differ. While plant-based diets have benefits for climate, food security and health,^{2, 3} they also increase the risk of nutritional deficiencies, including calcium, iodine, choline, essential amino acids and fatty acids, and vitamins B2, B12, and D.

Vitamin B12 is the most critical nutrient in vegan diets, as it is found almost exclusively in animal-source foods. B12 deficiency is endemic among vegans, and somewhat less so among vegetarians,⁴ as it is in India where (nearly) vegan diets are common.⁵ Complications of B12 deficiency include neurological deficit which can become irreversible, anaemia and other haematological abnormalities, malabsorption, osteoporosis, mental illness, dementia and stroke.⁶

Prevalence of B12 deficiency is increasing, through the growing popularity of vegan and vegetarian lifestyles, recreational use of nitrous oxide, and ageing of the population.⁷

Doctors are ill-prepared to manage prevention, diagnosis and treatment of B12 deficiency. Nutrition science and taking a dietary history receives little attention in their training. There is confusion about the recommended daily allowance – the UK advises 1.5 mcg daily for adults, the US 2.4 mcg, while research indicates that up to 10 mcg in divided doses is needed.⁸ Many doctors are unaware of the wide range and variation in symptoms and risk factors for B12 deficiency, and of the low sensitivity of the B12 test.⁹ Most laboratories do not offer the more sensitive metabolic tests. Many patients experience diagnostic delay for years or even decades,¹⁰ increasing their risk of permanent neurological deficit. In treatment, there is no validated instrument to record neurological symptoms for monitoring of treatment efficacy and compliance.

Plant-based diets require considerable nutritional competence, determination and perseverance with diet and supplementation regimens. Recommending plant-based diets to all our patients, regardless of age, comorbidity or nutritional literacy, and in a mere sentence, is a recipe for serious complications – both for the individual and for public health.

References
1. Storz MA. Mitigating climate change: using the physician’s tool of the trade. Br J Gen Pract 2019; 69(688): 557. 
2. Orlich MJ, Pramil J et al. Vegetarian Dietary Patterns and Mortality in Adventist Health Study 2. JAMA Intern Med 2013; 173(13): 1230-1238. 
3. Song M, Fung TT et al. Association of Animal and Plant Protein Intake With All-Cause and Cause-Specific Mortality. JAMA Intern Med 2016; 176(10):1453-1463 
4. Herrmann W, Schorr H et al. Vitamin B-12 status, particularly holotranscobalamin II and methylmalonic acid concentrations, and hyperhomocysteinemia in vegetarians. Am J Clin Nutr 2003; 78(1): 131-6. 
5. Yajnik CS, Deshpande SS et al. Vitamin B12 Deficiency and Hyperhomocysteinemia in Rural and Urban Indians. J Assoc Physicians India 2006; 54(Oct): 775-782. 
6. Spence DJ. Metabolic vitamin B12 deficiency: a missed opportunity to prevent dementia and stroke. Nutr Res 2016; 36(2): 109-116. 
7. Clarke R, Grimley Evans J et al. Vitamin B12 and folate deficiency in later life. Age Ageing 2004; 33(1): 34-41. 
8. Smith AD, Warren MJ et al. Vitamin B 12. In: Eskin, NAM ed. New Research and Developments of Water-Soluble Vitamins. Amsterdam: Academic press; 2018. p. 215-279. 
9. Ward MG, Kariyawasam VC et al. Prevalence and Risk Factors for Functional Vitamin B12 Deficiency in Patients with Crohn’s Disease. Inflamm Bowel Dis 2015; 21(12): 2839-2847. 
10. Hooper M, Hudson P et al. Patient journeys: diagnosis and treatment of pernicious anaemia. Br J Nurs 2014; 23(7): 376-81.