What are the best sources of vitamin B12 for vegetarians? Can milk and yogurt make up an adequate daily intake?
1. General vegetarians (Non-vegans)
For non-vegans, dairy products seems to be the best source, as mentioned in other answers as well. List of top 4 (I'm excluding eggs):
The amount of vitamin B12 in cheese depends on type and variety, Swiss cheese provides the most with 3.34μg per 100g serving (56% DV), followed by Gjetost(40% DV), Mozzarella(39% DV), Tilsit(35% DV), and Feta(28% DV).
2: Whey Powder
Once thought the sole domain of body builders, whey powder is now entering main stream as more people are going vegetarian. Whey powder is a common addition to breads and smoothies, 100 grams will provide 2.5 μg of vitamin B12 or 42% of the DV.
3: Milk and Yogurt
100 grams of non-fat yogurt provides 0.53μg (10% DV) of vitamin B12 and 15%DV per cup. 100 grams of reduced fat milk provides 0.46μg (8% DV) and 19% DV per cup.
4: Yeast extract Spreads (Marmite)
Yeast extract spreads are popular in Britain and Europe, and have started to gain popularity in the U.S. A good vegetarian source of protein, the spread also packs a lot of vitamin B12. One hundred grams provides 0.5μg (8% DV) of vitamin B12, that is 0.03μg (1% DV) per teaspoon.
As a vegan, I personally rely on nutritional yeast and multivitamins. There are some important points which are worth learning more about:
Is B12 Vegan?
The vitamin B12 component in B12 supplements and fortified foods is made by bacteria and sourced from bacteria cultures; it is not taken from animal products. However, some companies might put gelatin in their B12 supplements, though this appears to be less and less common. It is easy to find vegan B12 supplements on the Internet or in grocery stores in developed countries.
There are some live food supplement companies that rely on spirulina or other algae, rather than bacteria cultures, as a source of vitamin B12. You should not rely on such products for your vitamin B12 as testing has indicated it is not a reliable source of active vitamin B12 (more information).
Streptomyces griseus, a bacterium once thought to be a yeast, was the commercial source of vitamin B12 for many years (8, 9). The bacteria Propionibacterium shermanii and Pseudomonas denitrificans have now replaced S. griseus (10). At least one company, Rhone Poulenc Biochimie of France, is using a genetically engineered microorganism to produce B12 (11).
There are many vegan foods fortified with B12. They include non-dairy milks, meat substitutes, breakfast cereals, and one type of nutritional yeast.
The "Daily Value" for B12 found on food labels is based on 6 µg, which was the RDA in 1968. If a label says a food has, for example, 25% of the Daily Value of B12, it has 1.5 µg (25% of 6 µg = 1.5 µg).
Brewer's and Nutritional Yeasts
Brewer's and nutritional yeasts do not contain B12 unless they are fortified with it. There is at least one vegan, B12-fortified yeast currently on the market: Red Star Vegetarian Support Formula. (Twinlab's SuperRich Yeast Plus contains whey).
Tucker et al. (2000, USA, 13) found that vitamin B12 from fortified breakfast cereals and dairy products was associated with better vitamin B12 status than was B12 intake from red meat, poultry, and fish, leading the researchers to suspect that the B12 from meat might be damaged by cooking. The B12 in animal foods tends not to be cyanocobalamin, the form used in fortified foods and that is more stable during cooking. For example, in an acid medium (pH 4-7), cyanocobalamin can withstand boiling at 120° C (1).
Even so, for people wondering whether they are destroying the B12 in their fortified foods by cooking, we do not have enough evidence to know for certain, so it is safest to make sure you rely on uncooked sources of vitamin B12.
Animal products in general are really good sources of B12. This applies to milk and the products that are made from it and I would argue that eggs are a good source of it too, although your definition might be different.
This RDI for B12 was previously set to be 6µg but is now being changed to 2.4µg. Based on this, following can be said:
Milk is a very good source of B12 and one cup of milk can provide you with about 1.1µg of B12 which is almost half of the recommended 2.4µg RDI. Depending on how big of a milk drinker you are, you can probably get most of your B12 from milk and other dairy products.
While I know that you asked about vegetarian sources of B12, when talking about milk and B12, I must also mention vegan milk-substitutes which are usually also fortified with B12 and are a viable (and arguably more ecological, if that is your thing) alternative. If you decide to try, make sure to check whether that particular milk is fortified.
According to the USDA, one cooked egg (50g) contains 0.56µg of vitamin B12. The recommended daily intake of B12 for people age 14 and older who aren't pregnant or breastfeeding is 2.4µg.
Consuming eggs could therefore definitely help you achieve your daily intake in your balanced vegetarian diet.
Another thing that you might consider as a vegetarian are breakfast cereals, which are often being fortified with vitamins such as B12 or D. These are also great to combine with milk so you can have your B12 bomb in the morning and not worry for the rest of the day.
From my experience of being vegetarian for about 5 years before going vegan, I have never had to worry about my B12 intake particulary because of milk being rather good source (I never liked eggs) and my love for breakfast cereals.
In some countries (Canada), meat substitutes (e.g. soy-based hot-dogs) are required by law to be fortified (see Foods to Which Vitamins, Mineral Nutrients and Amino Acids May or Must be Added) -- which is why you can read something like,
Vitamin B12 is found only in animal foods and fortified foods. People who avoid all animal products should look for meat alternatives, such as soy products fortified with vitamin B12.
Or, if you're not vegan, other data on that page says that you need about 3 micrograms/day, which is contained in 3 oz Emmental or 2 cups of milk (but less in other processed milk products such as Yoghurt).