Introduction: Individuals following vegan and vegetarian diets are at an increased risk of vitamin B12 deficiency due to the absence of animal-based foods, the primary natural sources of this vitamin1. Despite the growing popularity of these diets, there is limited up-to-date comprehensive data on the prevalence of vitamin B12 deficiency among vegans and vegetarians of European ancestry residing in Western Europe or the USA. 
Primary Objectives: To provide a consensus on the prevalence of vitamin B12 deficiency among vegans and vegetarians of European ancestry residing in Western Europe or the USA.
Methods: We identified studies from our systematic review of “Functional Vitamin B12 Status Among Adult Vegans” to develop a narrative review of the prevalence of B12 deficiency based on different biomarkers of B12 status among vegan and vegetarians of European ancestry residing in Western Europe or the USA. We then used pooled data from National Diet and Nutrition Survey (NDNS)2 to calculate UK-specific prevalence information on B12 deficiency and insufficiency using the new NICE3 criteria among vegan/vegetarian women of child-bearing age (WCBA) (age 18-45) compared with older women.
Results: A total six studies (2013-2022) with data on the prevalence of B12 deficiency were identified. These studies were conducted on participants from UK, Norway, Spain, Czech Republic and US and nearly all used different cut-offs to define B12 deficiency. The prevalence of deficiency varied widely. Among vegans and vegetarians, the reported prevalence of deficiency ranged from 5-52% and 6-14%, respectively, with some studies (Norway4 and Finland5) highlighting low prevalence (5%) and no difference between these dietary groups, possibly due to widespread supplement usage. Research from the USA6, indicated a higher prevalence of inadequate B12 intake among vegans and vegetarians compared to omnivorous individuals, with 8% of vegans and 6% of vegetarians exhibiting serum B12 levels < 148 pmol/l. Similarly, results from Spain7 noted subclinical deficiencies in 11% of participants, in both vegans and vegetarians. In the Czech Republic8, cobalamin deficiency was noted in 15% of vegans, with 16.9% exhibiting laboratory signs of deficiency (Serum B12< 100 ng/L). Notably, regular supplementation significantly reduced deficiency rates, emphasising its pivotal role in maintaining normal B12 levels. In the UK9, only one publication reported B12 deficiency rates (SerumB12 <118pmol/L) among male vegans (52%) and vegetarians (7%). 
Using data from the NDNS and NICE guidelines, we calculated the prevalence of B12 deficiency (defined as serum B12 < 133 pmol/L and Holo-TC <25 pmol/L) at 5-8% among vegetarian women of child-bearing age (WCBA Age 18-45); appropriate data on vegans was not available. Vitamin B12 insufficiency (potential deficiency), defined by NICE as serum B12 < 258 pmol/L and Holo-TC < 70 pmol/L, translated to 75% of vegetarians within the WCBA cohort being defined as insufficient compared to 39% among older vegetarian women. Surprisingly, of the WCBA cohort 56% of omnivores were also classed as insufficient. A similar but more pronounced trend emerges for Holo-TC insufficiency, with 90% of vegetarians exhibiting inadequate Holo-TC < 70 pmol/L, compared to 58% of older women vegetarians and 65% of omnivores.
Conclusions: There are few published studies that report vitamin B12 deficiency among vegan and vegetarians of Western European ancestry. There is a particularly urgent need for appropriate data from vegan WCBA. The existing piecemeal data, highlights a potentially high risk of B12 deficiency among vegans and vegetarians which regular and appropriate use of vitamin B12 supplementation of adequately B12-fortified foods can correct.

References:
1.	Niklewicz, A., Smith, A.D., Smith, A. et al. (2023). Eur J Nutr  62, 1551–1559. 
2.	 National diet and nutrition survey (NDNS) (2023). National Diet and Nutrition Survey Years 1-11, 2008-2019. 19th Edition. UK Data Service. [data collection]. [Available at: DOI: http://doi.org/10.5255/UKDA-SN-6533-19].
3.	NICE guideline [NG239] (2024). Vitamin B12 deficiency in over 16s: diagnosis and management. [Available at: Overview | Vitamin B12 deficiency in over 16s: diagnosis and management | Guidance | NICE] 
4.	Henjum, S. et al. (2023).  Br J Nutr 129(12), 2076–2083.
5.	Elorinne, Anna-Liisa et al. (2016). PloS one, 11,2 e0148235. 
6.	Haddad EH, Jaceldo-Siegl K, Oda K, Fraser GE (2020). Curr Dev Nutr ;4(2): nzaa008. 
7.	Gallego-Narbón A, Zapatera B, Barrios L, Vaquero MP. (2019) J Nutr Sci ;8:e7.
8.	Selinger E, Kühn T, Procházková M, Anděl M, Gojda J. (2019) Nutrients;11(12):3019.
9.	Gilsing AM, Crowe FL, Lloyd-Wright Z, et al. (2010). Eur J Clin Nutr, 64(9):933-939. 



OC179 - What is the prevalence of vitamin B12 deficiency among healthy vegans and vegetarians of European ancestry residing in Western Europe or the USA?

Unique to the new Congress (previously the Summer Conference) is that you will have greater opportunity to engage with more nutrition science than ever before. In 2024 the core programme will be delivered by the Irish Section of The Nutrition Society, supported by the Science Committee. The theme of these symposia will be ‘new data – focused approaches and challenges’. Outside of the core programme you will have the chance to hear the latest research from the Society’s partner organisations, universities, the private sector and more, on a diverse range of research.