Vitamin B12, as the name implies, is part of the B complex of vitamins. Like the other B vitamins, it is involved in energy metabolism and other related biological processes.
However, that is where the similarity ends. The list of things that are unique about this vitamin is long, and includes the following facts:
As the list above implies, optimal intake of vitamin B12 can sometimes be a challenge in human nutrition. Even though U.S. adults ages 20 and older average well above the Dietary Reference Intake (DRI) for B12, there are still subgroups within the U.S. that are more commonly at risk of B12 deficiency. For example, adults 51 and older can be at greater risk of B12 deficiency, presumably in relationship to decreased dietary intake and/or compromised digestive function.
The style of diet that you choose can have an major impact on your B12 nourishment. If you regularly consume land animal foods and fish in your meal plan, B12 intake is not very likely to be a problem. If you regularly consume fish but avoid land animal foods, B12 is still relatively unlikely to be a problem. With no fish or land animal foods in your routine diet, however, you are left with some fairly specific food sources of B12, namely, fermented foods such as tempeh and fungi (including mushrooms). We'll give you some practical steps for obtaining B12 nourishment in the Food Sources section.
We list eight excellent sources of vitamin B12 on World's Healthiest Foods. We also have three very good and four good sources of the vitamin. Although the number of good sources is smaller than for many foods, this should be plenty to ensure a strong supply of this critical nutrient.
Vitamin B12 plays several important roles in keeping our cardiovascular system on track. The first of these roles involves production of red blood cells. Red blood cells are critical for transporting oxygen throughout our bloodstream, and the oxygen-carrying pigment in the center of our red blood cells is called hemoglobin. A key building block for hemoglobin is a compound called succinylCoA, and without enough vitamin B12, we simply cannot make enough of this building block. (Methylmalonyl CoA mutase is the enzyme that allows this process to take place, and it only functions with the help of B12 in the form of adenosylcobalamin.)
The fact that B12 plays such a key role in red blood cell production means that deficiency of this vitamin can actually cause a form of anemia called B12 deficiency anemia. However, this form of anemia is relatively rare. Often, when it appears to occur, it is actually a by-product of pernicious anemia in which immune system antibodies interfere with the production or function of intrinsic factor (IF). IF is a glycoprotein produced by specialized stomach cells called parietal cells and it is required for proper metabolism of vitamin B12.
A second important role for B12 in cardiovascular support involves prevention of excessive homocysteine build-up. A long list of cardiovascular diseases have been associated with excessive accumulation of homocysteine in the bloodstream, including coronary heart disease, peripheral vascular disease, and stroke. Vitamin B12 helps normalize levels of homocysteine in the blood by allowing conversion of homocysteine to methionine. (This conversion process takes place through activity of the enzyme methionine synthase.)
Vitamin B12 is a necessary co-factor for the production of DNA, the genetic material that acts as the backbone of all life. This process requires folate and vitamin B6 as well, and disruptions of any of these nutrients can lead to problems.
The diagnosis of vitamin B12 deficiency is often dependent on problems with DNA production. When vitamin B12 is low, normally rapidly dividing blood cells are not able to effectively reproduce their DNA, leading to abnormally big cells. This phenomenon, called macrocytosis, is often the first way doctors suspect problems with the vitamin.
Along with the heart, liver, muscles, and kidneys, the brain is an organ that utilizes a large amount of energy in a form called aerobic energy. Aerobic energy means oxygen-requiring energy production in specialized cell parts called mitochondria. As described earlier in the Cardiovascular Support section, one role that B12 plays is maintenance of hemoglobin in red blood cells to allow successful transport of oxygen. This process is especially important in brain health.
Another role of B12 described in the Cardiovascular Support section was prevention of excessive homocysteine build-up in the blood through conversion of homocysteine to methione. However, one aspect of this process not described earlier is the simultaneous recycling of a molecule called SAMe (S-adenosylmethionine) that takes place along with homocysteine conversion. SAMe has sometimes been referred to as the "universal methyl donor" because of its unique ability to provide special chemical groups—called methyl groups—in many different places where they are needed. One such place is the brain and nervous system, where movement of methyl groups is a key process. Some of the nervous system messengers (neurotransmitters) cannot be produced without the help of enzymes called methyltransferases, and these enzymes in turn cannot be produced without the availability of methyl groups. This area of methyl metabolism is another key way in which vitamin B12 plays a major role in the health of our brain and nervous system.
These nervous system connections to B12 help explain some of the clinical symptoms associated with B12 deficiency. When levels of vitamin B12 get very low, nerve damage can ensue. The insulation sheath around nerve fibers begins to break down, making it harder for signals to get to more distant areas of the body (called peripheral areas). As you might guess, symptoms first become apparent in the hands and feet. While the exact mechanisms are not fully understood, researchers know that severe B12 deficiency can cause these "peripheral neuropathies" and that restoring optimal supplies of B12 can keep these problems from becoming more severe.
While mentioned earlier, it's important to underscore the role of B12 in support of oxygen-based energy production (called aerobic energy). At the heart of this process is a metabolic cycle called the citric acid cycle and included within this cycle is a molecule called succinyl-coA. Since vitamin B12 is important for maintaining proper supplies of succinyl-coA in the citric acid cycle, it is important for supporting all aerobic energy metabolism.
Still under debate by researchers is the exact role of B12 in support of bone health. On the one hand, B12 deficiency appears to be associated with increased risk of osteoporosis. This connection involves the positive role of B12 (in several of its cobalamin forms) in supporting the activity of the osteoblast (bone-forming) cells. At the same time, B12 also appears to help regulate activity of tumor necrosis factor (TNF). TNF overactivity can result in too much bone breakdown and remodeling by a second type of bone cells called osteoclasts. Too much osteoclast activity—regardless of the reason for its occurrence—is also associated with increased risk of osteoporosis. Despite these logical connections between B12 deficiency and osteoporosis risk, however, actual research findings are inconsistent in making the B12 connection to bone status.
Microorganisms—and perhaps only bacteria and algae —are the only life forms capable of synthesizing vitamin B12. There has been longstanding debate over algal production of B12, which includes debate over the potential role of sea vegetables to provide B12 (as well as debate over dietary supplements like spirulina). However, we interpret the research in this area to show that sea vegetables cannot be counted on for B12 support, not because there is no possibility of B12 production in sea vegetables, but because production may vary widely and because the form of B12 in sea vegetables may not be a readily usable vitamin form.
Even though land animals and fish cannot make vitamin B12 in their cells, they are often able to save up B12 produced by bacteria and concentrate it in their cells. For this reason, many land animal foods and many seafoods are nutrient-rich in B12. In fact, all but one of our WHFoods ranked sources of B12 come from animal foods or fish. Because plants do not concentrate or utilize vitamin B12 in the same way as animals, plant foods do not become nutrient-rich in B12 unless they have been fermented (like the fermentation of soybeans into tempeh) by B12-producing bacteria. Mushrooms are a uniquely controversial food with respect to B12 content. Because scientists classify mushrooms in their own separate category of life form - fungi - they cannot be lumped together with plants from a science perspective. (On our website, we adopt a less technical perspective and include mushrooms in our vegetable plant group. And it is worth noting that crimini mushrooms are the only non-animal food that serves as a ranked source of B12 on our website.) The controversy over B12 and mushrooms is three-fold: (1) B12 is not always detected in mushrooms, including crimini mushrooms; (2) when B12 is detected in mushrooms, it is usually found on the outermost portions of the mushrooms, suggesting that bacteria on the mushroom surface may have been produced the B12 rather than the mushrooms themselves; and (3) the chemical structure of B12 found on some mushrooms - while based on the corrin-type ring structure characteristic of B12 - can have important differences from the form of B12 that provides us with full vitamin benefits. So while you may be getting a B12 boost from consumption of mushrooms like crimini mushrooms, we cannot recommend reliance on fungi as a primary source of B12.
Our recommended daily intake level for B12 is 2.4 micrograms, and one serving of any of the following WHFoods will provide you with 100% or more of this amount: sardines, salmon, tuna, cod, lamb, or scallops. You'll get over 50% with a single serving of beef or shrimp, about one-third of the daily amount from one cup of yogurt, and between 10-25% from one serving of cheese, chicken, turkey, eggs, or cow's milk.
In contrast with these animal and fish foods, one cup of crimini mushrooms will only provide you with about 3% of the daily recommend amount. This relatively low contribution from mushrooms (a non-animal food) raises the important question of B12 nourishment for individuals who don't regularly consume animal foods or fish. In the broadest sense, individuals who focus primarily on plant foods in their meal plan are often referred to as "vegetarians." However, this term can have a variety of different meanings. "Pesca-vegetarians," for example, consume fish along with plant foods. "Lacto-vegetarians" consume dairy foods along with plants foods. "Lacto-ovo vegetarians" consume not only dairy foods but also eggs along with plant foods. If a person eats plant foods exclusively, the term usually used to describe his or her meal plan is "vegan." Most healthcare providers—including most nutritionists—currently recommend that persons who exclusively consume plant foods take steps to ensure their B12 nourishment by adding foods fortified with B12 or B12-containing supplements to their daily routine. As a general rule, we support this approach, although we realize that there can be exceptions.
Nutritional yeast grown on a molasses medium is an example of a food-based quasi-supplement that would provide a vegan source of vitamin B12. One widely available brand has more than twice the Dietary Reference Intake (DRI) for B12 in one and one-half tablespoons of yeast. Not all nutritional yeasts are rich in vitamin B12, however, and you'll need to check labels for details.
Before leaving the topic of B12 and food sources, we want to go one step further in explaining some ongoing speculation about the relationship between B12, bacteria, and human nutrition. As described earlier, bacteria and other microorganisms are the only life forms that can be described as definitively able to produce B12. Interestingly, however, research studies have shown that bacteria capable of producing B12 can live inside our human intestinal tract. (One example of a bacterium known to produce B12 and also able to colonize parts of our digestive tract is Propionibacterium shermanii.) Furthermore, it seems likely that B12-producing bacteria are able reside in the very last segment of our small intestine known as the terminal ileum.The terminal ileum is especially important for vitamin B12 nourishment since it is the primary site for B12 absorption. In this last segment of our small intestine, however, there aren't nearly as many bacteria as are present in our large intestine. (We're talking about a minimum of 10,000 times less, and probably more like one million times less.) So exactly how much B12 contribution could potentially be made by B12-producing bacteria in the terminal ileum is an open question. While we don't see any justification for relying on bacterial production of B12 in our intestines as a source of this vitamin, it is also impossible for us to totally rule out this possible pathway for B12 nourishment and hopefully we will get some further clarification here in future research.
Nutritional yeast grown on a molasses medium is an example of a food-based quasi-supplement approach that would provide a vegan source of vitamin B12. One widely available brand has more than twice the Recommended Dietary Allowance (RDA) for B12 in one and one-half tablespoons of yeast. Note that not all nutritional yeasts are rich in vitamin B12, and that you'll need to check labels for details.
The National Academy of Sciences currently recommends that people over the age of 50 receive much of their vitamin B12 from supplements or fortified foods. Currently, about 40% of the vitamin B12 that Americans eat comes from these non-food sources. In addition to the fortified yeast discussed above, soy products and breakfast cereals often contain this type of added vitamin B12.
|World's Healthiest Foods ranked as quality sources of|
|Beef||4 oz||175.0||1.44||60||6.2||very good|
|Yogurt||1 cup||149.4||0.91||38||4.6||very good|
|Cow's milk||4 oz||74.4||0.55||23||5.5||very good|
|Eggs||1 each||77.5||0.55||23||5.3||very good|
|Mushrooms, Crimini||1 cup||15.8||0.07||3||3.3||good|
Density>=7.6 AND DRI/DV>=10%
Density>=3.4 AND DRI/DV>=5%
Density>=1.5 AND DRI/DV>=2.5%
Even though the structure of vitamin B12 is complicated, it is a relatively stable molecule to storage and cooking. Most of the B12 losses that we have seen from the cooking of B12-rich foods fall into the range of 10-50%. At the 50% end of the spectrum, most of the studies have involved boiling. Since B12 is a water-soluble vitamin, that finding makes sense to us, and it is one of the reasons that we generally prefer steaming over boiling, and when we do boil, it is for a relatively short period of time. The Healthy Sauté methods and braising methods that we use for fish generally take only 5-10 minutes of cooking time, and the same is true for steaming in recipes where fish are steamed. For meats, we often use a Quick Broil method that only involves dry heat. In short, we believe that you can count on substantial B12 nourishment from our B12-rich foods if you take advantage of our WHFoods cooking methods.
For most U.S. adults, the risk of dietary deficiency of vitamin B12 is quite low. The median intake of vitamin B12 in the United States and Canada has been variously estimated between 3 and 7 mcg per day. As such, most people are getting plenty of this vitamin to prevent deficiency.
The only group where we see any substantial risk of dietary vitamin B12 deficiency is in strict vegans (who consume no animal or fish foods whatsoever). In a group of 232 British vegans, most of whom were younger than age 50, a little more than half had biochemical evidence of dietary vitamin B12 deficiency. The deficiency risk was nearly ten times as high in vegans as vegetarians, and more than 50 times higher compared to those who regularly ate animal foods.
Ovo-lacto vegetarians (or people who don't eat animal meat or fish, but do include dairy and eggs in their diet) are at a slightly increased risk of dietary vitamin B12 deficiency, but B12-related medical problems are not common in this group. When medical problems do show up, it is most commonly in people who had eaten a vegetarian diet throughout their entire life, rather than adopting it later on as adults. This pattern makes sense to us, because our bodies are capable of storing large amounts of B12. In fact, it is common for adults to store thousands of times more B12 than their daily requirement. Because significant amounts of B12 are also be recycled around the body, the unusually large body supply of this vitamin can mean years before B12 depletion. So it is logical for an adult vegetarian who ate animal foods and fish growing up to go for long periods before risking B12 depletion, even if B12 intake has been inadequate.
The most common cause of vitamin B12 deficiency symptoms in the U.S. is not a dietary deficiency, but a problem related to malabsorption. This condition is called pernicious anemia, and it is a relatively common condition in older adults. An estimated 10-30% of people over the age of 50 have some amount of malabsorption of this vitamin.
In pernicious anemia, various immune system reactions cause damage to the stomach lining. As a result of this damage, specialized cells in the stomach called parietal cells become unable to produce intrinsic factor (IF). Since IF is needed for B12 absorption, this process results in poor absorption of B12, and the need for much greater amounts of B12 than can be obtained from food. Of course, diagnosis of this condition and the appropriate remedy for pernicious anemia requires the help of a licensed healthcare provider.
Pernicious anemia is not the only absorption-related problem associated with risk of vitamin B12 deficiency. As mentioned at the outset of this article, B12 is an unusual B-complex vitamin in terms of its absorption. Here is a short summary of the complicated nature of B12 absorption:
(1) Stomach acids are needed to release B12 from our food and allow it to bind with a glycoprotein called haptocorrin provided in saliva and in stomach fluids.
(2) When leaving the stomach, protease enzymes provided by the pancreas are needed to separate B12 from haptocorrin and allow it to bind together with intrinsic factor (IF). IF is a specialized glycoprotein release by specialized stomach cells called parietal cells, and its job is to bind together with B12 and facilitate its absorption.
(3) At the very end of the small intestine (called the terminal ileum), intestinal cells have special locations on their outer membranes (consisting of two proteins called cubulin and amionless) and these proteins serve as the location for taking the IF-bound form of B12 out of the intestine and up into the cells.
(4) Once inside the intestinal cells, B12 must be reconfigured and attached to a different protein called transcobalamin for passage through the bloodstream.
These many different digestive tract steps make B12 absorption readily influenced by digestive tract problems. For example, overgrowth of the bacterium Helicobacter pylori in the stomach has been associated with increased risk of B12 deficiency. Insufficient secretion of protein-digesting enzymes by the pancreas has also been shown to compromise B12 status. Various other stomach problems have also been associated with increased deficiency risk for this vitamin.
The connection between B12 deficiency risk and digestive problems is believed to be a primary reason for increased risk of B12 deficiency with aging (especially after age 50), since digestive problems also tend to increase during this time period.
While oral contraceptive (OC) use is sometimes mentioned as a risk factor for B12 deficiency, the research seems mixed in this regard. On the one hand, blood levels of B12 have been shown to sometimes drop below the normal range with OC use. But at the same time, these drops in blood levels appear to be temporary and to pose no chronic problems. Interestingly, lower blood levels of B12 in women who use OCs appear to occur independently from dietary intake. In other words, these lower levels of B12 do not appear to change, even if dietary intake of B12 is increased. More research is being done to determine the significant of these findings.
Pregnancy and lactation (breastfeeding) increase the need for B12, and the Dietary Reference Intake (DRI) recommendations for pregnancy and lactation are 2.6 micrograms and 2.8 micrograms, respectively.
Because folate and B12 work so closely together, both folate deficiency and folate excess can increase the need for B12. While folate excess has been controversial in health research primarily in relationship to dietary supplementation of this vitamin in high doses, some scientists believe that folate fortification of food (in the absence of simultaneous B12 fortification) can also create imbalances in the ratio of B12-to-folate. As a remedy, they have recommended simultaneous fortification with both folate and B12 if fortification is determined to be desirable. The bottom line here is to combine a reasonable variety of foods in your meal plan that are nutrient-rich in both B vitamins. Our Healthy Sauteéd Seafood with Asparagus recipe, for example, combines three of our top 10 seafoods rich in B12 (cod, scallops, and shrimp) with our second richest source of folate (asparagus).
As described earlier in our Health Benefits section, vitamin B12 is involved in the process of energy production. Yet B12 is not the only B-complex vitamin involved in this process, and for this reason, a deficiency of one or more of the other B vitamins may compound energy-production problems that are related to B12 deficiency. In other words, some symptoms of B12 deficiency can be made worse due to other B-vitamin deficiencies.
In particular, the relationship between folic acid, vitamin B6, and vitamin B12 is very close. A deficiency in any one of the three can impair the activity of the others. Most alarmingly, when people use high dose supplements of folic acid, it can be harder to spot vitamin B12 deficiency, leading to more serious symptoms. As described earlier in this article, controversy has also arisen over the role of folate fortification of foods, which has some researchers recommending simultaneous fortification of both folate and B12 whenever fortification with either nutrient is being considered.
Some older sources report that vitamin C can damage or impair absorption of vitamin B12. Further research discounted this hypothesis, so you can probably disregard this if you see it.
There is no known toxicity risk from dietary vitamin B12. In fact, doctors routinely inject people with deficiency symptoms with very large doses of the vitamin—500 times the daily required intake or more—without evidence of toxicity. You can be confident that your diet does not contain too much vitamin B12.
In 1998, the National Academy of Sciences established a set of Dietary Reference Intakes (DRI) that included Recommended Dietary Allowances (RDA) by age for vitamin B12. These are summarized in the chart below. Values for infants under one year old were established in the form of Adequate Intake (AI) levels. The full set of DRI recommendations is listed below:
Note that the National Academy of Sciences has advised people over the age of 50 to meet their intake requirements mainly via either fortified foods or using a vitamin B12 supplement. This recommendation is due to the high number of people in this age group with malabsorption of the vitamin.
There is no established Tolerable Upper Intake Level (UL) for vitamin B12. In fact, doctors rather routinely supplement or inject people with pernicious anemia with amounts of vitamin B12 that are several hundred-fold greater than the DRI recommendations. As such, there is no known reason to be concerned about excessive intake of vitamin B12.
The Daily Value (DV) of 6 mcg per day is the value you'll see on food labels. Please note that the more recent DRI values are much lower, and probably a better reflection of your daily needs. We chose the adult DRI (ages 14 and older) of 2.4 micrograms as our daily recommended amount at WHFoods.