Stay in Touch
Get sneak previews of special offers & upcoming events delivered to your inbox.
-
Blogs & Forums
Turn on suggestions
Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.
Showing results for
From The National Institute of Health comes this excellent resource. Almost everything you should know is included and is explained. Good information to keep filed for reference. Sorry for the small print but I think you can enlarge it. The interactions with specific medications is very helpful. One thing not included in the NIH report is the association with thyroid problems and B12. There’s plenty of research on this. I know one poster was asking about this in a different thread.
Vitamin B12 is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement and a prescription medication. Vitamin B12 exists in several forms and contains the mineral cobalt [1-4], so compounds with vitamin B12 activity are collectively called “cobalamins
Methylcobalamin and 5-deoxyadenosylcobalamin are the forms of vitamin B12 that are active in human metabolism [5].
Vitamin B12 is required for proper red blood cell formation, neurological function, and DNA synthesis [1-5]. Vitamin B12 functions as a cofactor for methionine synthase and L-methylmalonyl-CoA mutase. Methionine synthase catalyzes the conversion of homocysteine to methionine [5,6]. Methionine is required for the formation of S-adenosylmethionine, a universal methyl donor for almost 100 different substrates, including DNA, RNA, hormones, proteins, and lipids. L-methylmalonyl-CoA mutase converts L-methylmalonyl-CoA to succinyl-CoA in the degradation of propionate [3,5,6], an essential biochemical reaction in fat and protein metabolism. Succinyl-CoA is also required for hemoglobin synthesis.
Vitamin B12, bound to protein in food, is released by the activity of hydrochloric acid and gastric protease in the stomach [5]. When synthetic vitamin B12 is added to fortified foods and dietary supplements, it is already in free form and, thus, does not require this separation step. Free vitamin B12 then combines with intrinsic factor, a glycoprotein secreted by the stomach’s parietal cells, and the resulting complex undergoes absorption within the distal ileum by receptor-mediated endocytosis [5,7]. Approximately 56% of a 1 mcg oral dose of vitamin B12 is absorbed, but absorption decreases drastically when the capacity of intrinsic factor is exceeded (at 1–2 mcg of vitamin B12) [8].
Pernicious anemia is an autoimmune disease that affects the gastric mucosa and results in gastric atrophy. This leads to the destruction of parietal cells, achlorhydria, and failure to produce intrinsic factor, resulting in vitamin B12 malabsorption [3,5,9-11]. If pernicious anemia is left untreated, it causes vitamin B12 deficiency, leading to megaloblastic anemia and neurological disorders, even in the presence of adequate dietary intake of vitamin B12.
Vitamin B12 status is typically assessed via serum or plasma vitamin B12 levels. Values below approximately 170–250 pg/mL (120–180 picomol/L) for adults [5] indicate a vitamin B12 deficiency. However, evidence suggests that serum vitamin B12 concentrations might not accurately reflect intracellular concentrations [6]. An elevated serum homocysteine level (values >13 micromol/L) [12] might also suggest a vitamin B12 deficiency. However, this indicator has poor specificity because it is influenced by other factors, such as low vitamin B6 or folate levels [5]. Elevated methylmalonic acid levels (values >0.4 micromol/L) might be a more reliable indicator of vitamin B12 status because they indicate a metabolic change that is highly specific to vitamin B12 deficiency [5-7,12].
Recommended Intakes
Intake recommendations for vitamin B12 and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine (IOM) of the National Academies (formerly National Academy of Sciences) [5]. DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and gender [5], include:
Table 1 lists the current RDAs for vitamin B12 in micrograms (mcg) [5]. For infants aged 0 to 12 months, the FNB established an AI for vitamin B12 that is equivalent to the mean intake of vitamin B12 in healthy, breastfed infants.
Table 1: Recommended Dietary Allowances (RDAs) for Vitamin B12 [5]Age Male Female Pregnancy Lactation
| 0–6 months* | 0.4 mcg | 0.4 mcg | ||
| 7–12 months* | 0.5 mcg | 0.5 mcg | ||
| 1–3 years | 0.9 mcg | 0.9 mcg | ||
| 4–8 years | 1.2 mcg | 1.2 mcg | ||
| 9–13 years | 1.8 mcg | 1.8 mcg | ||
| 14+ years | 2.4 mcg | 2.4 mcg | 2.6 mcg | 2.8 mcg |
* Adequate Intake
Sources of Vitamin B12 Food
Vitamin B12 is naturally found in animal products, including fish, meat, poultry, eggs, milk, and milk products. Vitamin B12 is generally not present in plant foods, but fortified breakfast cereals are a readily available source of vitamin B12 with high bioavailability for vegetarians [5,13-15]. Some nutritional yeast products also contain vitamin B12. Fortified foods vary in formulation, so it is important to read the Nutrition Facts labels on food products to determine the types and amounts of added nutrients they contain.
Several food sources of vitamin B12 are listed in Table 2.
Table 2: Selected Food Sources of Vitamin B12 [13]
Food Micrograms (mcg)per serving Percent DV*
| Clams, cooked, 3 ounces | 84.1 | 1,402 |
| Liver, beef, cooked, 3 ounces | 70.7 | 1,178 |
| Nutritional yeasts, fortified with 100% of the DV for vitamin B12, 1 serving | 6.0 | 100 |
| Trout, rainbow, wild, cooked, 3 ounces | 5.4 | 90 |
| Salmon, sockeye, cooked, 3 ounces | 4.8 | 80 |
| Trout, rainbow, farmed, cooked, 3 ounces | 3.5 | 58 |
| Tuna fish, light, canned in water, 3 ounces | 2.5 | 42 |
| Cheeseburger, double patty and bun, 1 sandwich | 2.1 | 35 |
| Haddock, cooked, 3 ounces | 1.8 | 30 |
| Breakfast cereals, fortified with 25% of the DV for vitamin B12, 1 serving | 1.5 | 25 |
| Beef, top sirloin, broiled, 3 ounces | 1.4 | 23 |
| Milk, low-fat, 1 cup | 1.2 | 18 |
| Yogurt, fruit, low-fat, 8 ounces | 1.1 | 18 |
| Cheese, Swiss, 1 ounce | 0.9 | 15 |
| Beef taco, 1 soft taco | 0.9 | 15 |
| Ham, cured, roasted, 3 ounces | 0.6 | 10 |
| Egg, whole, hard boiled, 1 large | 0.6 | 10 |
| Chicken, breast meat, roasted, 3 ounces | 0.3 | 5 |
*DV = Daily Value. The U.S. Food and Drug Administration (FDA) developed DVs to help consumers compare the nutrient contents of products within the context of a total diet. The DV for vitamin B12 used for the values in Table 2 is 6.0 mcg for adults and children age 4 years and older [16]. This DV, however, is changing to 2.4 mcg as the updated Nutrition and Supplement Facts labels are implemented [17]. The updated labels and DVs must appear on food products and dietary supplements beginning in January 2020, but they can be used now [18]. FDA does not require food labels to list vitamin B12 content unless a food has been fortified with this nutrient. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.
The U.S. Department of Agriculture’s (USDA’s) FoodData Central
Web site [13]) lists the nutrient content of many foods and provides a comprehensive list of foods containing vitamin B12 arranged by nutrient content and by food name.
Dietary supplements
In dietary supplements, vitamin B12 is usually present as cyanocobalamin [5], a form that the body readily converts to the active forms methylcobalamin and 5-deoxyadenosylcobalamin. Dietary supplements can also contain methylcobalamin and other forms of vitamin B12.
Existing evidence does not suggest any differences among forms with respect to absorption or bioavailability. However the body’s ability to absorb vitamin B12 from dietary supplements is largely limited by the capacity of intrinsic factor. For example, only about 10 mcg of a 500 mcg oral supplement is actually absorbed in healthy people [8].
In addition to oral dietary supplements, vitamin B12 is available in sublingual preparations as tablets or lozenges. These preparations are frequently marketed as having superior bioavailability, although evidence suggests no difference in efficacy between oral and sublingual forms [19,20].
Prescription medications
Vitamin B12, in the form of cyanocobalamin and occasionally hydroxocobalamin, can be administered parenterally as a prescription medication, usually by intramuscular injection [12]. Parenteral administration is typically used to treat vitamin B12 deficiency caused by pernicious anemia and other conditions that result in vitamin B12 malabsorption and severe vitamin B12 deficiency [12].
Vitamin B12 is also available as a prescription medication in a gel formulation applied intranasally, a product marketed as an alternative to vitamin B12 injections that some patients might prefer [21]. This formulation appears to be effective in raising vitamin B12 blood levels [22], although it has not been thoroughly studied in clinical settings.
Vitamin B12 Intakes and Status
Most children and adults in the United States consume recommended amounts of vitamin B12, according to analyses of data from the 1988–1994 National Health and Nutrition Examination Survey (NHANES III) [5,23] and the 1994–1996 Continuing Survey of Food Intakes by Individuals [5]. Data from the 1999–2000 NHANES indicate that the median daily intake of vitamin B12 for the U.S. population is 3.4 mcg [24].
Some people—particularly older adults, those with pernicious anemia, and those with reduced levels of stomach acidity (hypochlorhydria or achlorhydria) or intestinal disorders—have difficulty absorbing vitamin B12 from food and, in some cases, oral supplements [25,26]. As a result, vitamin B12 deficiency is common, affecting between 1.5% and 15% of the general population [27,28]. In many of these cases, the cause of the vitamin B12 deficiency is unknown [8].
Evidence from the Framingham Offspring Study suggests that the prevalence of vitamin B12 deficiency in young adults might be greater than previously assumed [15]. This study found that the percentage of participants in three age groups (26–49 years, 50–64 years, and 65 years and older) with deficient blood levels of vitamin B12 was similar. The study also found that individuals who took a supplement containing vitamin B12 or consumed fortified cereal more than four times per week were much less likely to have a vitamin B12 deficiency.
Individuals who have trouble absorbing vitamin B12 from foods, as well as vegetarians who consume no animal foods, might benefit from vitamin B12-fortified foods, oral vitamin B12 supplements, or vitamin B12 injections [29].
EDITED TO ADD THAT PART 2 OF THIS POST HAS MORE INTERESTING INFORMATION THAN PART 1. I HOPE YOU’LL TAKE A LOOK. It contains interactions between medicines and B12.
*You're signing up to receive QVC promotional email.
Manage Your Account
Find recent orders, do a return or exchange, create a Wish List & more.
Get More with QCard®
Enjoy Your QCard Easy Pay Perk!
Customer Service
Work with Us
Stay Connected
Download Our QVC Apps
This is Shopping Brought to Life.
Privacy StatementGeneral Terms of Use
QVC is not responsible for the availability, content, security, policies, or practices of the above referenced third-party linked sites nor liable for statements, claims, opinions, or representations contained therein. QVC's Privacy Statement does not apply to these third-party web sites.
© 1995-2024 QVC, Inc. All rights reserved. | QVC, Q and the Q logo are registered service marks of ER Marks, Inc. 888-345-5788