The Most Undervalued Supplement: Vitamin B12
According to the Institute of Medicine, Vitamin B12 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 , so compounds with vitamin B12 activity are collectively called “cobalamins.”.
The Institute of Medicine notes that Vitamin B12 is required for proper red blood cell formation, neurological function, and DNA synthesis . The most active forms of B12 in human metabolism are Methylcobalamin and 5-deoxyadenosylcobalamin.
According to the Harvard School of Public Health, Vitamin B12 binds to the protein in the foods we eat. In the stomach, hydrochloric acid and enzymes unbind vitamin B12 into its free form. From there, vitamin B12 combines with a protein called intrinsic factor so that it can be absorbed further down in the small intestine.
B12 in its free form(more easily absorbed) can be found in supplements and fortified foods. There is a variety of vitamin B12 supplements available. HSPH points out that although there are claims that certain forms—like sublingual tablets or liquids placed under the tongue to be absorbed through the tissues of the mouth—have better absorption than traditional tablets, studies have not shown an important difference.
It’s important to distinguish between the available dosage of Vitamin B12 in tablets vs the amount that will be absorbed which is usually very different because an adequate amount of intrinsic factor is also needed. In cases of severe vitamin B12 deficiency due to inadequate intrinsic factor (pernicious anemia), doctors may prescribe B12 injections in the muscle.
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). 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, include:
- Recommended Dietary Allowance: The RDA, the estimated amount of a nutrient (or calories) per day considered necessary for the maintenance of good health by the Food and Nutrition Board of the National Research Council/ National Academy of Sciences.
- Adequate Intake (AI): The AI is the recommended average daily intake level based on observed or experimentally determined approximations or estimates of nutrient intake by a group (or groups) of apparently healthy people that are assumed to be adequate – used when an RDA cannot be determined.
- Estimated Average Requirement (EAR): EAR is the amount of a nutrient that is estimated to meet the requirement for a specific criterion of adequacy of half of the healthy individuals of a specific age, sex, and life-stage.
- Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.
Table 1 lists the current Recommended Dietary Allowance for vitamin B12 in micrograms (mcg). 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.
|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|
Vitamin B12 Defciency
Weight loss, constipation, loss of appetite, fatigue, weakness, and Megaloblastic anemia can all be signs of vitamin B12 deficiency. Additional symptoms of vitamin B12 deficiency include depression, confusion, soreness of the mouth or tongue, difficulty maintaining balance, poor memory, and dementia .
Neurological changes, such as tingling and numbness in the hands and feet, can also occur with or without anemia, so early diagnosis and intervention is important to avoid irreversible damage.
Many of the symptoms that we are discussing here are very general and could result from a variety of medical conditions other than vitamin B12 deficiency. For example during infancy, signs of a vitamin B12 deficiency are subtle and require close attention, such signs include developmental delays, failure to thrive, movement disorders, and megaloblastic anemia.
Typically, vitamin B12 deficiency is treated with vitamin B12 injections, since this method bypasses potential barriers provides the highest absorption rate. However, high doses of oral vitamin B12 may also be an effective alternative.
The authors of a review of randomized controlled trials, published in Public Health Wales, compared oral with intramuscular vitamin B12 and concluded that 2,000 mcg of oral vitamin B12 daily, followed by a decreased daily dose of 1,000 mcg and then 1,000 mcg weekly and finally, monthly might be as effective as intramuscular administration.
Overall, an individual patient’s ability to absorb vitamin B12 is the most important factor in determining whether vitamin B12 should be administered orally or via injection. In most countries, the practice of using intramuscular vitamin B12 to treat vitamin B12 deficiency has remained unchanged.
Natural Sources of Vitamin B12
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. 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 according to fdc.nal.usda.gov
|Food||Micrograms per serving||Percent DV|
|Clams, cooked, 3 ounces||84.01||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||5.8||80|
|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|
|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|