Water Soluble Vitamins

8 B vitamins and Vitamin C

What are vitamins:

• essential compounds for growth and metabolism

• organic compounds

• only necessary in trace amounts

Water soluble vitamins vs fat soluble vitamins:

• water soluble are absorbed directly into blood, while fat soluble are absorbed in lymph within chylomicrons.

• water soluble vitamins are not stored for long, therefore must be consumed regularly in diet. Fat soluble vitamins are stored in fat cells or fatty tissue. Not easily excreted.

• water soluble vitamins are rarely toxic, while fat vitamins are likely toxic from supplements, as they are not excreted when in excess.

What are the B group vitamins?

B1: thiamine

B2: riboflavin

B3: niacin

B5: pantothenic acid

B6: pyridoxine

B7: biotin

B9: folate

B12: cobalamins

Thiamine functions:

• forms part of the coenzyme TPP which is involved in converting pyruvate to acetyl CoA.

Thiamine deficiency (Beriberi):

• common in populations that eat predominantly white rice, as the germ part of the grain contains thiamine.

• dry beriberi and wet beriberi

• there is also a type of alcohol induced form of thiamine deficiency called Wernicke Korsakoff syndrome common in alcoholics. This is because alcohol displaces food from the diet, lowering thiamine intake as well as increasing excretion of thiamine in urine.

Wet beriberi:

• affects the heart and circulatory system before nerve and brain damage are obvious.

• increased heart rate

• vasodilation

• shortness of breath on exertion

• edema of lower legs

• can be fatal due to heart failure and weakening of capillary walls.

Dry beriberi

Damaged peripheral nerves resulting in wasting and partial paralysis.

• brain damage and peripheral nerve damage are symptomatic before heart failure begins.

• difficulty walking

• tingling or numbness in hands and feet

• loss of muscle function or lower leg paralysis

• vomiting.

Food sources of thiamine:

• whole grains

• meat and fish

• pork, sunflower seeds, watermelon, fortified cornflakes, soy milk.

• lost from grains in milling (removing germ of grain) and destroyed by prolonged heating or cooking in water.

Thiamine toxicity symptoms:

none known

Vitamin B2 / Riboflavin functions:

• part of the coenzyme FAD, therefore involved in reactions moving hydrogen atoms and electrons from TCA cycle to ETC.

Food sources of riboflavin:

• dairy

• meat

• leafy vegetables

• cereals

• eggs

• liver

• fortified cereals.

Riboflavin deficiency symptoms

• inflamed eyelids

• light sensitivity

• sore throat

• cracks at corners of mouth

• painful smooth purple tongue

• skin inflammation with greasy scales

Riboflavin toxicity symptoms:

• none known

Function of Vitamin B3/Niacin

• forms two co-enzymes: NAD and NADP

• both participate in metabolic reactions, carrying H and high energy electrons from TCA cycle to electron transport chain.

Food sources of Niacin

• liver

• meat

• fish

• mushrooms

• fortified breakfast cereal

• some niacin can be made by the body by tryptophan however this is inefficient - 60 trp molecules for 1 niacin.

Niacin toxicity symptoms:

• painful skin flush, hives and rash

• excessive sweating

• blurred vision

• liver damage

• impaired glucose

• large doses may lower blood cholesterol levels.

Niacin deficiency symptoms:

• diarrhea, dermatitis, dementia, eventual death. (4 ds)

• skin darkens and flakes away as if sunburned. Only occurs on body parts exposed to sunlight.

Vitamin B5 / pantothenic acid - functions in the body:

• energy metabolism

• a precursor of coenzyme A, and therefore needed to metabolise many molecules.

• involved in over 100 metabolic steps, mostly in its coenzyme form (coenzyme A).

• lipid synthesis

• a critical component of acetyl-CoA.

Food sources of pantothenic acid:

• organ meats

• meat

• wholegrain cereals

• brocoli

• avocadoes

Pantothenic acid deficiency:

• rare since vitamin B5 is in such a wide variety of fod

• general failure of body systems with nervous system faults being early signs (insomnia and fatigue) followed by nausea and vomiting.

• no known toxicity symptoms.

Vitamin B6/Pyridoxine functions:

• the active coenzyme forms are PLP and PMP.

• primary function is in amino acid metabolism. Can help synthesise non-essential amino acids by transferring amino groups from one amino acid to other compounds such as keto acids.

• can be stored in muscle tissue, unlike other water soluble vitamins.

Drug interactions with vitamin B6:

• a TB inhibiting drug binds to vitamin B6 leading to B6 deficiency.

• Alcohol

Food sources of Pyridoxine:

• meat, fish, poultry

• fortified cereals

• vegetables

• can be lost by heating food.

Deficiency symptoms

• weakness

• kidney stones

• irritability

• insomnia

• anaemia

• depression

Toxicity from Pyridoxine

• difficult to achieve toxicity from normal dietary intake

• some women using supplements for PMS experience nerve damage, bloating, depression, headaches.

Functions of vitamin B7 - Biotin

• acts as a coenzyme for the reaction of CO2 with pyruvate to form oxaloacetate, which is needed for the TCA cycle.

• otherwise the acetyl CoA entering TCA cycle would have insufficient oxaloacetate to react with.

Food sources of Biotin

• liver

• green leafy vegetables.

• GI bacteria can make small amounts

Biotin deficiency

• rare due to wide food availability and small amount needed.

• deficiency can occur from overconsumption of raw egg whites, which contain the protein avidin, which binds to and prevents absorption of biotin.

• symptoms: nausea, appetite loss, depression, fatigue, dry skin.

Biotin toxicity symptoms:

none known

Folate / Vitamin B9 - Role in the body:

• It’s active coenzyme form is called THF.

• THF is important in adding or removing methyl groups during metabolic processes.

• Is inactive when carrying a methyl group, and becomes activated when B12 removes the methyl group, activating both compounds.

• important in cell division and growth

• important in DNA and RNA synthesis.

How Folate is processed in the body

• in food, folate has many glutamates attached.

• during digestion, all glutamates but one are removed before absorption.

• Once absorbed, a methyl group is attached, inactivating the methyl-THF.

• Activation occurs when vitamin B12 (cobalamin) removes the methyl group, activating both compounds.

Folate deficiency:

• cell division and protein synthesis is impaired - red blood cells and GI tract especially.

• A vicious cycle for GI tract absorption, with injury to the GI tract leading to greater folate deficiency, which leads to lower absorption of other nutrients.

• Megablastic anaemia: large, immature red blood cells that often still have a nucleus. This is due to issues in cell division caused by low folate.

• Deficiency in folate during pregnancy is linked to neural tube defects of the baby. eg: spina bifida. Mandatory fortification of bread was introduced in 2009.

• critical period for neural tube development during pregnancy is the first trimester - folate supplements are advised.

Food sources of folate

• liver,

• legumes

• vegetables

• fortified foods

• folate is destroyed easily by cooking.

• no toxicity symptoms identified.

Vitamin B12 - Cobalamin: functions in the body

• activates methyl-THF folate by removing the methyl group. As folate assists in cell division and synthesis of DNA and RNA, cobalamin facilitates this too.

• Maintains the myelin sheath around nerve fibres.

• Important in bone activity and metabolism.

Cobalamin digestion and transport:

• attached to proteins in food and is removed by HCl and pepsin in the stomach.

• a glycoprotein carrier is attached to B12 in the stomach, allowing absorption into bloodstream.

Food sources of Cobalamin:

• only found in animal foods like meat, milk, cheese, eggs

• vegans need to consume fortified foods or supplements.

B12 deficiency:

• more likely in vegans and the elderly

• usually due to poor absorption, including low stomach HCl or lack of intrinsic factor/glycoprotein carrier.

• symptoms include pernicious anaemia

• can lead to folate deficiency as B12 is needed to activate methyl-THF folate.

• often confused with folate deficiency.

Overall function of B vitamins:

• usually form part of a coenzyme for metabolic reactions

• particularly relevant in reactions that release energy from macronutrients (cellular respiration).

Vitamin C functions:

1. As an antioxidant:

• the reduced form of vitamin C (ascorbic acid) is oxidised to dehydroascorbic acid, which allows two hydrogen atoms and their electrons to be donated to free radicals.

• oxidised in preference to other substances, protecting the body from oxidation.

2. Collagen formation:

• iron is used as a cofactor in the process of forming collagen. Since iron often causes redox reactions, vitamin C keeps it in its correct oxidative state.

Vitamin C deficiency symptoms:

• scurvy: bleeding gums, failure to make collagen

• internal hemorrhaging, muscle degeneration, dry skin, infections, death.

Factors that deplete vitamin C:

• body stressors such as smoking, aspirin, wounds, infection

• hormones such as norepinephrine require vitamin C in the metabolism of amino acids during their formation.

vitamin C toxicity

• tissues are saturated with vitamin C at levels of 100mg per day.

• excess is excreted in urine.

• intake above 1-2g per day can lead to nausea, diarrhoea and abdominal cramps

• can interfere with anticoagulants

• kidney stones