Vitamin B12 is a water-soluble vitamin that's in virtually all meat products and certain algae, such as seaweed, that helps maintain healthy nerve and red blood cells and is also needed to make DNA, the genetic material in all cells. Good sources of vitamin B12 include meat, salmon, cod, milk, cheese, eggs, yeast extract, and some fortified breakfast cereals. As it is found almost exclusively in animal-based products, if you cut out animal products from your diet, you can be at risk of B12 deficiency.
Vitamin B12 deficiency symptoms usually develop gradually but can worsen if the condition goes untreated. They include headaches, fatigue, pale skin, and palpitations. Pernicious anaemia (an autoimmune condition) prevents absorption by stopping the production of intrinsic factor and is the leading cause of vitamin B12 deficiency.