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 what are sources of vitamin b12 medication. Vitamin B12 exists in several forms and contains the mineral cobalt [ ], 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 [ ]. Vitamin B12 functions as a cofactor for methionine synthase and L-methylmalonyl-CoA mutase. Methionine synthase catalyzes the conversion of homocysteine to methionine [ 56 ].
Methionine is required for the formation of S-adenosylmethionine, a universal methyl donor for almost 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 [ 356 ], 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. Pernicious anemia is an autoimmune disease that affects the gastric mucosa and results in gastric atrophy. This leads to the destruction of parietal cells, what are sources of vitamin b12, achlorhydria, and failure to produce intrinsic factor, resulting in vitamin B12 malabsorption [ 35].
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 B Vitamin B12 status is axis insurance plan arizona assessed via serum or plasma vitamin B12 levels.
However, evidence suggests that serum vitamin B12 concentrations might not accurately reflect intracellular concentrations [ 6 ]. However, this indicator has poor specificity because it is influenced by other factors, such as low vitamin B6 or folate levels [ 5 ], what are sources of vitamin b12.
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 what are sources of vitamin b12 micrograms mcg [ 5 ], what are sources of vitamin b12. 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.
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]. Some nutritional yeast products also contain vitamin B Fortified foods vary in formulation, so it is important to read product labels to determine which added nutrients they contain. 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. This DV, however, is changing to 2. The updated labels and DVs must appear on food products and dietary supplements beginning in Januarybut 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.
In dietary supplements, vitamin B12 is usually present as cyanocobalamin [ 5 ], a form that the body readily converts to what are sources of vitamin b12 active what are sources of vitamin b12 methylcobalamin and 5-deoxyadenosylcobalamin. Dietary supplements can also contain methylcobalamin and other forms of vitamin B Existing evidence does not suggest any differences among forms with respect to absorption or bioavailability.
For example, only about 10 mcg of a mcg oral supplement is actually absorbed in healthy people [ 8 ]. In addition to oral dietary supplements, what are sources of vitamin b12, vitamin B12 is available in sublingual preparations as tablets or lozenges. These preparations are frequently marketed as having superior bioavailability, antique distributor caps evidence suggests no difference in efficacy between oral and sublingual forms [ 1920 ].
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 What are sources of 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.
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 [ 2526 ].
As a result, vitamin B12 deficiency is common, affecting between 1. In many of these cases, what are sources of vitamin b12, 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 what are sources of vitamin b12 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 dog eye antibiotics 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 Bfortified foods, oral vitamin B12 supplements, or vitamin B12 injections [ 29 ].
Vitamin B12 deficiency is characterized by megaloblastic anemia, fatigue, weakness, constipation, loss of appetite, and weight loss [ 1330 ], what are sources of vitamin b12. Neurological changes, such as numbness and tingling in the hands and feet, can also occur [ 531 ]. Additional symptoms of vitamin B12 deficiency include difficulty maintaining balance, depression, confusion, dementia, poor memory, and soreness of what are sources of vitamin b12 mouth or tongue [ 32 ].
The neurological symptoms of vitamin B12 deficiency can occur without anemia, so early diagnosis and intervention is important to avoid irreversible damage [ 6 ]. During infancy, signs of a vitamin B12 deficiency include failure to thrive, movement disorders, developmental delays, and megaloblastic anemia [ 33 ]. Many of these symptoms are general and can result from a variety of medical conditions other than vitamin B12 deficiency.
Typically, vitamin B12 deficiency is treated with vitamin B12 injections, since this method bypasses potential barriers to absorption. However, high doses of oral vitamin B12 may also be effective.
The authors of a review of randomized controlled trials comparing oral with intramuscular vitamin B12 concluded that 2, mcg arthritis in tailbone oral vitamin B12 daily, followed by a decreased daily dose of 1, mcg and then 1, mcg weekly and finally, monthly might be as effective as intramuscular administration [ 2728 ].
In most countries, what are sources of vitamin b12, the practice of using intramuscular vitamin B12 to treat vitamin B12 deficiency has remained unchanged [ 27 ]. Large amounts of folic acid can mask the damaging effects of vitamin B12 deficiency by correcting the megaloblastic anemia caused by vitamin B12 deficiency [ 35 ] without correcting the neurological damage that also occurs [ 1what are sources of vitamin b12, 34 ].
Moreover, what are sources of vitamin b12, preliminary evidence suggests that high serum folate levels might not only mask vitamin B12 deficiency, but could also exacerbate the anemia and worsen the cognitive symptoms associated with vitamin B12 deficiency [ 611 ]. Permanent nerve damage can what are sources of vitamin b12 if vitamin What are sources of vitamin b12 deficiency is not treated. For these reasons, folic acid intake from fortified food and supplements should not exceed 1, mcg daily in healthy adults [ 5 ].
The main causes of vitamin B12 deficiency include vitamin B12 malabsorption from food, pernicious anemia, postsurgical malabsorption, and dietary deficiency [ 12 ]. However, in many cases, the cause of vitamin B12 deficiency is unknown. The following groups are among those most likely to be vitamin B12 deficient. Decreased hydrochloric acid levels might also increase the growth of normal intestinal bacteria that use vitamin B12, what are sources of vitamin b12, further reducing the amount of vitamin B12 available to the body [ 40 ].
Individuals with atrophic gastritis are unable to absorb the vitamin B12 that is naturally present in food. Most, however, can absorb the synthetic vitamin B12 added to fortified foods and dietary supplements.
As a result, the IOM recommends that adults older than 50 years obtain most of their vitamin B12 from vitamin supplements or fortified foods [ 5 ]. However, some elderly patients with atrophic gastritis require doses much higher than the RDA to avoid subclinical deficiency [ 41 ].
Individuals with pernicious anemia cannot properly absorb vitamin B12 in the gastrointestinal tract [ 35910 ]. Pernicious anemia is usually treated with intramuscular vitamin B Subtly reduced cognitive function resulting from early vitamin B12 deficiency might be the only initial symptom of these intestinal disorders, followed by megaloblastic anemia and dementia. Surgical procedures in the gastrointestinal tract, such as weight loss surgery or surgery to remove all or part of the stomach, often result in a loss of cells that secrete hydrochloric acid and intrinsic factor [ 54243 ].
This reduces the amount of vitamin B12, particularly food-bound vitamin B12 [ 44 ], that the body releases and absorbs. Surgical removal of the distal ileum also can result in the inability to absorb vitamin B Individuals undergoing these surgical procedures should be monitored preoperatively and postoperatively for several nutrient deficiencies, what are sources of vitamin b12, including vitamin B12 deficiency [ 45 ].
Strict vegetarians and vegans are at greater risk than lacto-ovo vegetarians and nonvegetarians of developing vitamin B12 deficiency because natural food sources of vitamin B12 are limited to animal foods [ 5 ]. Fortified breakfast cereals are one of the few sources of vitamin B12 from plants and can be used as a dietary source of vitamin B12 for strict vegetarians and vegans. Vitamin B12 crosses the placenta during pregnancy and is present in breast milk.
Exclusively breastfed infants of women who consume no animal products may have very limited reserves of vitamin B12 and can develop vitamin B12 deficiency within months of birth [ 546 ].
Undetected and untreated vitamin B12 deficiency in infants can result in severe and permanent neurological damage. The American Dietetic Association recommends supplemental vitamin B12 for vegans and lacto-ovo vegetarians during both pregnancy and lactation to ensure that enough vitamin B12 is transferred to the fetus and infant [ 47 ]. Pregnant and lactating women who follow strict vegetarian or vegan diets should consult with a pediatrician regarding vitamin B12 supplements for their infants and children [ 5 ].
Cardiovascular disease is the most common cause of death in industrialized countries, such as the United States, and is on the rise in developing countries. Risk factors for cardiovascular disease include elevated low-density lipoprotein LDL levels, high blood pressure, low high-density lipoprotein HDL levels, obesity, and diabetes [ 48 ].
Elevated homocysteine levels have also been identified as an independent risk factor for cardiovascular disease [ ]. Homocysteine is a sulfur-containing amino acid derived from methionine that is normally present in blood.
Elevated homocysteine levels are thought to promote thrombogenesis, impair endothelial vasomotor function, promote lipid peroxidation, and induce vascular smooth muscle proliferation [ 495052 ]. Evidence from retrospective, cross-sectional, and prospective studies links elevated homocysteine levels with coronary heart disease and stroke what are sources of vitamin b12 49]. Vitamin B12, folate, and vitamin B6 are involved what are sources of vitamin b12 homocysteine metabolism.
In the presence of insufficient vitamin B12, homocysteine levels can rise due to inadequate function of methionine synthase [ 6 ]. Results from several randomized controlled trials indicate that combinations of vitamin B12 and folic acid supplements with or without vitamin B6 decrease homocysteine levels in people with vascular disease or diabetes and in young adult women [ ]. Evidence supports a role for folic acid and vitamin B12 supplements in lowering homocysteine levels, but results from several large prospective studies have not shown that these supplements decrease the risk of cardiovascular disease [ 51].
The Heart Outcomes Prevention Evaluation HOPE 2 trial, which included 5, patients older than 54 years with vascular disease or diabetes, found that daily treatment with 2. In the Western Norway Microbial deterioration of antibiotics Vitamin Intervention Trial, which included 3, patients undergoing coronary angiography, daily supplements of 0.
The American Heart Association has concluded that the available evidence is inadequate to support a role for B vitamins in reducing cardiovascular risk [ 51 ].
Researchers have long been interested in the potential connection between vitamin B12 deficiency and dementia [ 5072 ]. A deficiency in vitamin B12 causes an accumulation of homocysteine in the blood [ 6 ] and might decrease levels of substances needed to metabolize neurotransmitters [ 73 ]. Low vitamin B12 status has also been positively associated with cognitive decline [ 75 ].