Functions
Three main enzymatic reactions regarding vitamin B12 have been noted to occur in humans. The first reaction requires methylcobalamin as a coenzyme in the conversion of homocysteine into methionine. This reaction occurs in the cytosol of the cell. The reaction is intrinsic to the production of tetrahydrofolate (THF). The production of THF is irreversible and requires vitamin B12, therefore, a B12 deficiency can trap folate in its methyl form (also known as the folate-methyl trap), which in turn affects purine and thymidylate synthesis.
Vitamin Mineral Supplements
A second set of reactions requiring B12 are those catalyzed by mutases. These reactions occur within the mitochondria. These include the production of succinyl CoA, a Krebs cycle intermediate. Mutase enzymes are also intrinsic in the oxidation of fatty acids. A defect in mutase activity results in impai.red muscle activity and an accumulation of methylmalonyl CoA and methylmalonic acid. The branched-chain amino acid leucine is also catalyzed by a mutase enzyme. Specifically, leucine undergoes isomerization, requiring adenosylcobalamin .
Sources
The only dietary sources of vitamin B12 are animal products. Plants and legumes are not good sources of vitamin B12, but may contain small quantities of B12 due to contamination with microorganisms during harvesting. Cobalamins are found in meat, meat products, poultry, fish, clams, oysters, and eggs. The bioavailability of the cobalamins depends on which form they are found in.
Governmental Recommended Intake
Two micrograms daily is the recommended daily intake for vitamin B12. Doses of vitamin C that are greater than 500 mg and taken within I hour of eating a meal may impair B12 absorption?
Deficiency symptoms
More than 95% of the B12 deficiencies diagnosed are related to inadequate absorption rather than inadequate dietary intake. Vitamin B12 deficiency occurs in stages of which changes within the cells and blood are primary. Vitamin B12 deficiency later results in megaloblastic anemia (this can also be caused by folate deficiency, therefore, it is best to treat with a combination of B12 and folate). Signs of progressive B12 deficiency include neuropathy, characterized by demyelination of nerves, and hyperhomocystinemia. The populations at greatest risk for a B12 deficiency do not include athletes, but rather the elderly, alcoholics, gastrectomy patients, and strict vegetarians (vegans).
Human Studies
In the late I980s a popular dietary supplement known as Dibencozide (a coenzyme of vitamin B12) was purported to have steroid-like properties. This was anecdotal and was never confirmed by research. Bodybuilders have also been known to use the injectable cyanocobalamin as a stimulant for appetite and muscle gain. This was due to the misunderstood role that B12 has in red blood cell and protein synthesis. To date, there has not been a reputable study illustrating an ergogenic effect of vitamin B12 or any of its cobalamin forms.
Christmas Sales Caltrate 600 Plus D Calcium Supplement Chewable Tablets with Vitamin D and Minerals, Assorted Fruit Flavors, 90-Count Bottles (Pack of 2) 201
Dec 08, 2011 21:33:33
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Christmas Sales Caltrate 600 Plus D Calcium Supplement Chewable Tablets with Vitamin D and Minerals, Assorted Fruit Flavors, 90-Count Bottles (Pack of 2) Feature
- Case of two bottles, each containing 90 chewable tablets of calcium and vitamin D dietary supplement (total of 180 chewable tablets)
- Made with cherry, orange, and fruit punch flavors
- Natural and artificial flavors
- Each easy-to-use bottle lasts up to 3 months
- Made in the United States
Christmas Sales Caltrate 600 Plus D Calcium Supplement Chewable Tablets with Vitamin D and Minerals, Assorted Fruit Flavors, 90-Count Bottles (Pack of 2) Overview
This dietary supplement comes in a chewable tablet form and is made with natural and artificial flavors including cherry, orange and fruit punch. Each tablet provides 600 mg of elemental calcium. Made in USA.SAVE NOW on Christmas Sales Offers below!
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