B12 deficiency is especially common in vegetarians and vegans.The takeaway most recent studies using more sensitive techniques for detecting B12 deficiency have found that 68% of vegetarians and 83% of vegans are B12 deficient, compared to just 5% of omnivores.
Vitamin B12 works together with folate in the synthesis of DNA. It’s also involved in the production of the myelin sheath around the nerves, and the conduction of nerve impulses. B12 deficiency can cause numerous problems, including:
•Anemia, cause tissue hypoxia (lack of Oxygen), 無氧代謝accumulate more acid in your body (酸性體質).
•poor immune function (low white blood cells, lymphocytes to fight virus, bacterial and cancer cells)
•Insomnia （頑固性失眠）
•Memory loss
•Neurological and psychiatric problems like severe depression, bipolar syndrome,anxiety）
•Cancer
•Bone pain
And much more…
A common myth amongst vegetarians and vegans is that it’s possible to get B12 from plant sources like seaweed, fermented soy, spirulina and brewers yeast. But plant foods said to contain B12 actually contain B12 analogs called cobamides that block the intake of, and increase the need for, true B12.
Vegan diets, in particular, are almost completely devoid of certain nutrients that are crucial for physiological function. Several studies have shown that both vegetarians and vegans are prone to not only deficiencies in B12, but also deficiencies of other nutrients like
1. calcium, iron, zinc (the bioavailability, means absorption, of the iron, calcium and zinc in plant foods is much lower than in animal foods.),
2. the long-chain fatty acids EPA & DHA,
Plant foods do contain linoleic acid (omega-6) and alpha-linolenic acid (omega-3), both of which are considered essential fatty acids. In this context, an essential fatty acid is one that can’t be synthesized by the body and must be obtained in the diet. However, an increasing body of research has highlighted the benefits of the long-chain omega-3 fatty acids EPA & DHA. These fatty acids play a protective and therapeutic role in a wide range of diseases: cancer, asthma, depression, cardiovascular disease, ADHD, and autoimmune diseases, such as rheumatoid arthritis.
While it is possible for some alpha-linolenic acid from plant foods to be converted into EPA & DHA, that conversion is poor in humans: between 5-10% for EPA and 2-5% for DHA. (10) Vegetarians have 30% lower levels of EPA & DHA than omnivores, while vegans have 50% lower EPA and nearly 60% lower DHA. (11) Moreover, the conversion of ALA to DHA depends on zinc, iron and pyridoxine—nutrients which vegetarians and vegans are less likely than omnivores to get enough of.
3. fat-soluble vitamins like A & D.
Perhaps the biggest problem with vegetarian and vegan diets, however, is their near total lack of two fat-soluble vitamins: A and D. Fat-soluble vitamins play numerous and critical roles in human health. Vitamin A promotes healthy immune function, fertility, eyesight and skin. Vitamin D regulates calcium metabolism, regulates immune function, reduces inflammation and protects against some forms of cancer.
These important fat-soluble vitamins are concentrated, and in some cases found almost exclusively, in animal foods: primarily seafood, organ meats, eggs and dairy products. Some obscure species of mushrooms can provide large amounts of vitamin D, but these mushrooms are rarely consumed and often difficult to obtain. (This explains why vitamin D levels are 58% lower in vegetarians and 74% lower in vegans than in omnivores.)
The idea that plant foods contain vitamin A is a common misconception. Plants contain beta-carotene, the precursor to active vitamin A (retinol). While beta-carotene is converted into vitamin A in humans, the conversion is inefficient. For example, a single serving of liver per week would meet the RDA of 3,000 IU. To get the same amount from plant foods, you’d have to eat 2 cups of carrots, one cup of sweet potatoes or 2 cups of kale every day. Moreover, traditional cultures consumed up to 10 times the RDA for vitamin A. It would be nearly impossible to get this amount of vitamin A from plant foods without juicing or taking supplements.
I do not think it’s possible to meet nutrient needs on a vegan diet without supplements—and quite a few of them. Vegan diets are low in B12, biovailable iron and zinc, choline, vitamin A & D, calcium, and EPA and DHA. It is difficult to justify a diet with low levels of several nutrients critical to human function. Please think twice of following the vegan diet. So if you’re intent on following a vegan diet, please make sure you are supplementing with those nutrients. Here is a ebook link for Vit B12 deficency
http://my.chriskresser.com/wp-content/uploads/membership-files/ebooks/B12%20Deficiency.pdf
Resource: http://chriskresser.com/b12-deficiency-a-silent-epidemic-with-serious-consequences
