Vitamin B : complex, shocking sources, bioavailability & risks related

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Vitamin B1 (Thiamin)

Thiamin is a sulfur-containing vitamin that participates in energy metabolism, converting carbohydrates,
lipids, and proteins into energy. Thiamin also plays a key role in nerve and muscle activity.

The primary sources of vitamin B1

Offal (liver, kidneys, heart), fish, meat (pork), whole grain cereals, leafy green vegetables, asparagus,
eggplant, fruits, legumes (beans and lentils), nuts, soymilk, squash, brewer’s yeast.

Bioavailability of vitamin B1

There is no data on the bioavailability of vitamin B1, but we know that levels in foods are very susceptible
to heat, cooking times, and length of storage. Vitamin B1 is also lost in the milling process, where the
bran layer and some of the germ layer that contains vitamins are removed from grains.

People who consume diets consisting of primarily refined grains (mostly milled flour and polished rice) are at risk for thiamin deficiency. The risk of inadequacy is less when food manufacturers fortify refined grains with vitamin B1.

Clinical vitamin B1 deficiency is called beriberi, a condition that still occurs in South-East Asia. In beriberi, there is damage to the nervous system characterized by muscle weakness in the arms and legs, or damage to the cardiovascular system which is characterized by dilated blood vessels, causing the heart to work harder and the kidneys to retain salt and water, resulting in edema.

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Vitamin B2 (Riboflavin)

Vitamin B2 participates in oxidation-reduction reactions, by accepting and then donating two hydrogen molecules, which are necessary for releasing energy from carbohydrates, fats, and proteins.

Vitamin B2 stimulates growth and reproduction, plays a role in vision, and in the conversion of vitamins B6, folic acid, and niacin into their active coenzyme forms.

The primary sources of vitamin B2

Vitamin B2 is found in offal (liver, kidneys, heart), eggs, meat, milk, yogurt, cheeses, whole grain cereals, dark green leafy vegetables, and brewer’s yeast.

Bioavailability of vitamin B2

Vitamin B2 from foods is highly available; bile salts, which are released when we consume fats, increase the rate of absorption of vitamin B2. Vitamin B2 is sensitive to light but remains stable under heat and refrigeration. The milling process reduces the content of vitamin B2 in cereal grains.

Individuals whose food intake relies primarily on refined cereals, the elderly, chronic dieters, and individuals who exclude milk products from their diet are at risk for inadequate intake. Vitamin B2 requirements are increased during periods of strong growth, such as in pregnancy and lactation.

Vitamin B2 deficiency co-occurs with other nutrient deficiencies and it may precipitate deficiencies in vitamin B6 and niacin. People with cardiovascular disease, diabetes, or cancer are at risk for vitamin B2 deficiency.

Vitamin B3 (Niacin)

Niacin acts as a coenzyme in energy-transfer reactions, especially the metabolism of glucose, fat, and alcohol. Niacin is similar to riboflavin coenzymes in that it carries hydrogen molecules (and their electrons) during metabolic reactions. It also protects against neurological degeneration.

Niacin is unique in that it can also be synthesized from the amino acid tryptophan. It occurs in two forms: niacinamide and nicotinic acid.

The primary sources of vitamin B3

Primary sources are offal (liver), fish, meat, milk, eggs, whole grain cereals, legumes, fruit (avocados, figs, dates, prunes), and nuts.

Other: Synthesized from tryptophan

Bioavailability of vitamin B3

Absorption of niacin depends on the food source. Niacin from meat, liver, beans, and fortified products is highly bioavailable. About 30% of the niacin in grains is bioavailable, though additional niacin can be released if the food undergoes alkali treatment (limewater/calcium hydroxide).

Compared to other water-soluble vitamins, niacin is less susceptible to losses during food storage. It is fairly heat resistant, so it can withstand reasonable cooking times. However, like other water-soluble vitamins, it will leach
into the cooking water.

Risks related to inadequate or excess intake of vitamin B3

Individuals whose diets do not meet their energy needs are therefore at risk of deficiency, as are individuals whose staple diet relies primarily on (untreated) maize or barley, and chronic alcoholics. Severe niacin deficiency results in a disease called pellagra and its symptoms are dermatitis, diarrhea, dementia, and eventually death.

The risk of excessive intake is unlikely if niacin is consumed from food sources. However, consumption of niacin in the form of nicotinic acid from multiple sources at high levels, including dietary supplements, pharmaceutical doses, and fortified foods, may result in adverse effects such as flushing, nausea and vomiting, liver toxicity, blurred vision, and impaired glucose tolerance.

Vitamin B5 (Pantothenic Acid)

Vitamin B5 is part of the structure of coenzyme A, the “crossroads” compound in several metabolic pathways, and is involved in more than 100 different steps in the synthesis of lipids, neurotransmitters, steroid hormones, and hemoglobin.

Vitamin B5 is important for the maintenance and repair of tissues and cells of the skin and hair, helps in the healing of wounds and lesions, and pantethine, which is a form of vitamin B5, normalizes blood lipid profiles.

The primary sources of vitamin B5

Vitamin B5 is found in offal (liver, kidneys), meat (chicken, beef), egg yolk, milk, fish, whole grain cereals, potatoes, tomatoes, broccoli, and mushrooms.

Other: synthesized by intestinal microorganisms but the contribution of this to nutrient status is unknown.

Bioavailability of vitamin B5

The bioavailability of pantothenic acid from food sources is about 50%. Although vitamin B5 is quite stable if heated, extended cooking times and prolonged high temperatures (such as boiling temperatures) can cause greater loss of the vitamin. Pantothenic acid is also destroyed in the process of freezing, canning, or refining.

Risks related to inadequate or excess intake of vitamin B5

Vitamin B5 deficiency is very rare and symptoms involve a general failure of all the body’s systems. Symptoms include fatigue, nausea, vomiting, headaches, and tingling sensations (“burning feet” syndrome). No adverse effects have been reported with high intakes of vitamin B5.

vitamin B
vitamin B

Vitamin B6 (Pyridoxine)

Vitamin B6 is required for the majority of biological reactions (i.e., amino acid metabolism, neurotransmitter
synthesis, red blood cell formation).

It occurs in three forms: pyridoxal, pyridoxine, and pyridoxamine. All can be converted to the coenzyme PLP (pyridoxal phosphate), which transfers amino groups from an amino acid to make nonessential amino acids, an action that is valuable in protein and urea metabolism.

The conversions of the amino acid tryptophan to niacin or to the neurotransmitter serotonin also depend on PLP. In addition, PLP participates in the synthesis of the heme compound in hemoglobin, of nucleic acids in DNA, and of lecithin, a fatty compound (phospholipid) that provides structures to our cells. Vitamin B6 is stored in muscle tissue.

The primary sources of vitamin B6

There are many good sources of vitamin B6, including chicken, liver (cattle, pig), and fish (salmon, tuna). Nuts (walnut, peanut), chickpeas, maize and whole grain cereals, and vegetables (especially green leafy vegetables), bananas, potatoes, and other starchy vegetables are also good sources.

Bioavailability of vitamin B6

If consuming a mixed diet, the bioavailability of vitamin B6 is about 75%. Vitamin B6 is destroyed by heat but it remains stable during storage.

A deficiency of vitamin B6 alone is uncommon; usually, it occurs in combination with a deficit in other B vitamins. Individuals at risk for poor intake are alcoholics and those taking tuberculosis medication. Signs of vitamin B6 deficiency include microcytic anemia due to inadequate synthesis of hemoglobin, depression, nerve problems, and irritability.

No adverse events have been observed with high intakes of vitamin B6.

Vitamin B7 (Biotin | Vitamin H)

Biotin plays an important role in metabolism as a coenzyme that transfers carbon dioxide. This role is critical in the breakdown of food (carbohydrates, fats, and proteins) into energy. Biotin is involved in many cellular reactions, particularly in the fat and protein metabolism of hair roots, fingernails, and skin.

The primary sources of vitamin B7

Eggs, milk, vegetables, cereals, nuts (almonds, walnuts, peanuts), liver, kidney, yeast, soybeans.

Other: synthesized by intestinal bacteria.

Bioavailability of vitamin B7

In foods, biotin is found in the free form or bound to dietary proteins. The bioavailability of biotin depends on the ability of protein enzymes in the stomach to convert protein-bound biotin to free biotin. Biotin is not sensitive to light, heat, or humidity.

Experts have yet to quantify the amount of biotin in natural foods. Deficiency due to lack of dietary intake is rare in healthy populations. Symptoms of deficiency include general fatigue, nausea, neurological problems, poor skin, and hair quality. No adverse effects have been reported with excessive intakes of biotin.

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Vitamin B9 (Folate)

Folate refers to the naturally occurring forms (pteroylglutamic acid) as well as the forms found in fortified foods and supplements (folic acid). Folic acid is the most stable form of folate.

The primary function of folate is as a coenzyme, THF (tetrahydrofolate), that transfers single-carbon compounds for DNA synthesis and repair and in energy and amino acid metabolism. Folate and vitamin B12 are interconnected in their capacity to donate and receive these single-carbon compounds, which are called methyl

For example, THF with a methyl group donates its carbon compound to vitamin B12. This action transforms vitamin B12 into an active coenzyme, which will in turn catalyze the conversion of homocysteine to methionine.

Without vitamin B12, folate in its methyl form becomes trapped inside cells, unavailable to support cell growth. Folate is essential for brain development and function.

The primary sources of folate

Dark green leafy vegetables, beans, lentils, asparagus, wheat germ, yeast, peanuts, oranges, and strawberries.

Bioavailability of folate

Folic acid from supplements is 100% bioavailable if taken without food, and 85% bioavailable when taken with food. Naturally occurring folates in food are 50% bioavailable, but the natural forms are highly unstable. Folate is easily destroyed by heat and oxygen.

Individuals with diets that lack sufficient quantity and variety of green leafy vegetables and legumes are at risk for inadequate folate intake. Folate requirements are increased during pregnancy, especially in the first couple of weeks of gestation.

Folate deficiency is highly associated with the risk of neural tube defects in the growing fetus. Thus, women of childbearing age and pregnant women are advised to meet folate requirements using a combination of natural foods (folate forms) and fortified foods or supplements (folic acid). In many Western countries, governments have mandated flours to be fortified with folate.

Because folate is critical for cell growth and repair, especially for cells with a short life span, such as cells in the mouth and digestive tract, visible signs of folate deficiency include digestive problems.

Other symptoms are tiredness, loss of appetite, fewer but larger red blood cells (megaloblastic or macrocytic anemia), and neurological problems. A vitamin B12 deficiency will provoke a folate deficiency because it means vitamin B12 is not available to donate its methyl group to convert folate into its active form.

Vitamin B12 (Cobalamin)

Vitamin B12 functions as a coenzyme in the conversion of homocysteine to methionine, in the metabolism of fatty acids and amino acids, and in the production of neurotransmitters. It also maintains a special lining that surrounds and protects nerve fibers, and bone cell activity depends on vitamin B12.

Folate and vitamin B12 are closely related. When folate gives up its methyl group to B12, it activates this vitamin.

The primary sources of vitamin B12

Vitamin B12 is found only in foods of animal origin, except where plant-based foods have been fortified. Rich sources of vitamin B12 include shellfish, liver, game meat (venison and rabbit), some fish (herring, sardines, salmon, trout), milk, and milk products.

Bioavailability of vitamin B12

While there is insufficient data on the absorption of vitamin B12, experts assume that about 50% of vitamin B12 is absorbed by adults with a healthy digestive tract. Inadequate absorption occurs when there is not enough acid in the stomach, or when a protein called intrinsic factor is not produced in the stomach. Conventional cooking methods involving high heat (e.g. microwave) and long cooking times may result in some vitamin B12 losses.

About 10–30% of older adults are estimated to have chronic inflammation of the stomach, a condition that impairs the absorption of vitamin B12. It is advised that older adults consume fortified foods or supplements to meet their vitamin B12 requirements.

Vegans (individuals who do not consume animal-source foods), who do not take fortified foods or supplements, will develop vitamin B12 deficiency.

However, it can take several years to develop a vitamin B12 deficiency because the body recycles much of its vitamin B12 by reabsorbing it over and over again. Infants born to vegan mothers are also at risk for deficiency if their mother’s vitamin B12 status was low during pregnancy.

Vitamin B12 requirements are increased for individuals who are HIV-positive with chronic diarrhea. Symptoms of vitamin B12 deficiency include anemia, general fatigue, loss of appetite, gastric atrophy, neuromuscular pain, and neurological problems (gait, memory loss). No adverse effects with excessive intakes of vitamin B12 have been reported.


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