Vitamin B12 bioavailability significantly decreases with increasing intake of this vitamin per meal. Vitamin B12 is partially degraded and loses its biological activity during cooking and storage of foods.
The intrinsic factor-mediated gastrointestinal absorption system in humans has evolved to selectively absorb active vitamin B12 from naturally occurring vitamin B12 compounds, including its degradation products and inactive corrinoids. This absorption system is estimated to be saturated at about 1.5 - 2.0 mcg of cobalamin (B12) per meal, 50% of dietary vitamin B12 is absorbed by healthy adults with normal gastro-intestinal function.
Some plant foods, dried green and purple lavers (nori) contain substantial amounts of vitamin B12, although other edible algae contained none or only traces of it. Most of the edible blue-green algae (cyanobacteria) used for human supplements predominantly contain pseudovitamin B12, which is inactive in humans.
The bioavailability of vitamin B12 in healthy humans from fish meat, sheep meat, and chicken meat averaged 42%, 56%-89%, and 61%-66%, respectively, in eggs it seems to be poorly absorbed (< 9%).
Minerals (nutrients) are inorganic substances (contain no carbon) that are necessary for normal body function and development.
Macro-minerals are needed in large doses (approximate recommended daily intake, milligrams (mg) per day ):
- potassium, K (3500 mg) - metal, ions are necessary for the function of all living cells;
- chloride, Cl− (3400 mg) - essential electrolyte in all body fluids;
- sodium, Na, natrium (2400 mg) - metal, essential for all animals and some plants;
- calcium, Ca (1000 mg) - metal, essential for living organisms, produced in supernova nucleosynthesis;
- phosphorus, P (1000 mg) - in the form of the phosphate is required for all known forms of life;
- choline (425 - 550 mg) - essential vitamin-like (vitamin B4) nutrient, synthesized in human body, but not sufficiently;
- magnesium, Mg (350 mg) - metal, essential for all known living organisms;
Trace minerals are needed in very small amounts (recommended daily intake, milligrams (mg) or micrograms (mcg) per day:
- iron, Fe (15 mg) - metal, found in nearly all living organisms;
- zinc, Zn (8 - 11 mg) - metal, essential for humans and other organisms;
- manganese, Mn (5 mg) - metal, toxic essential trace element;
- fluorine, F, fluoride ion, F− (3 - 4 mg) - a beneficial poisonous element, essential for bone solidity;
- copper, Cu (2 mg) - metal, essential to all living organisms;
- iodine, I (150 mcg) - a key component of thyroid hormones;
- selenium, Se (35 mcg) - toxic in large doses, essential micronutrient for animals;
- chromium, Cr (30 mcg) - chromium (III) is questionably essential for humans.