25. Water-soluble vitamins

Page created on February 27, 2019. Last updated on December 18, 2024 at 16:57

General

B vitamins in general are found in highest abundance in meat and vegetables. Chronic alcoholics usually don’t consume much of either of these. Alcoholics also usually have liver problems, which may interfere with the storage of these vitamins (if they have stores) and their conversion to the active form. Because of these facts is complex vitamin B hypovitaminosis frequent in chronic alcoholics.

You may find that my notes disagree with the curriculum at some points. For example, the department claims that folic acid is vitamin B₁₁ and not B₉, which no other serious source supports. They also claim that the RDA for folic acid is 0.5-2 mg per day, while it is actually 0.4 mg per day in healthy adults and 0.6 mg per day in pregnant women. They also claim that vitamin C deficiency causes hypercholesterolaemia which has been proven in guinea pigs but is unheard of in humans.

You might want to “safe it” and go with the information the department teaches, or you can learn what’s actually true and try to argue with the examiner if you should get asked about it.

I include the updated values for RDA (for adult men) as presented by the Institute of Medicine, the government of USA. The values taught by the university are marked in italic.

Vitamin B₁

Name: Vitamin B₁ or thiamine

Function in the body:

Thiamine is the precursor for the cofactor TPP (thiamine pyrophosphate). TPP is essential for carbohydrate (glucose) metabolism.

Store in the body: Not significantly stored

Typical sources: Vegetables, eggs, meat, outer coat (husk) of grains

RDA: 1.2 mg (1-3 mg)

Typical causes for deficiency:

Decreased intake can occur in a diet with a lot of white rice (where the husk is removed) and white bread. Some foods like sea fish and brussels sprouts contain a thiaminase enzyme which degrades thiamine, however that should hardly be a problem unless you eat sea fish and brussels sprouts with every meal.

Thiamine deficiency is common in alcoholics. This population commonly have a poor diet (eat a lot of carbs and very little vegetables, eggs or meat). Ethanol also disturbs thiamine absorption by multiple mechanisms.

Deficiency can also occur when the requirement is increased. This may theoretically occur during too large consumption of carbohydrates, in pregnancy, lactation or in rapid growth.

Hypovitaminosis condition:

The hypovitaminosis of thiamine deficiency is called beriberi. There are two types, wet beriberi and dry beriberi. Underlying both types of beriberi is the fact that in thiamine deficiency tissues have problems producing enough ATP from blood glucose.

Wet beriberi is more typical for thiamine deficiency in Asia and mostly affects the cardiovascular system. When the smooth muscles of arterioles are deprived of thiamine are they unable to produce enough ATP from glucose to maintain their muscular tone. This causes vasodilation and a severe decrease in total peripheral resistance. To maintain the blood pressure should the cardiac output increase, either by tachycardia or increased stroke volume.

Due to ATP deficiency in the myocardium is the myocardium unable to increase the contractility (and thereby the stroke volume). The ventricles can’t dilate during diastole (as that requires ATP), causing end-diastolic pressure to increase with resulting dilatative hypertrophy. Congestion develops.

Congestion of the pulmonary circulation leads to cardiac dyspnoea. Tachycardia occurs to maintain cardiac output. Congestion of the systemic circulation leads to generalized oedema (thereby the name “wet”), ascites and hepatomegaly. CO is elevated but still deficient, potentially leading to high output cardiac failure.

Dry beriberi is more typical for the western world and mostly affects the peripheral and central nervous systems. Neural tissue has high energy (ATP) requirement. Due to the cellular ATP deficiency will myelin sheaths and axons be degenerated. This leads to paraesthesia (abnormal sensation on the skin), frequently with burning in the feet and hands. Muscle weakness, cramps and reflex abnormalities may develop.

ATP deficiency of CNS cells causes atrophy of several brain areas. Encephalopathy caused by thiamine deficiency is called Wernicke’s encephalopathy where headache and learning disability is common. Korsakoff psychosis may also occur, especially if the thiamine deficiency is caused by chronic alcoholism. In that case is there loss of short-term memory and confabulation.

The combined presence of Wernicke’s encephalopathy and Korsakoff psychosis in chronic alcoholics has coined the term Wernicke-Korsakoff syndrome for these patients.

Hypervitaminosis condition: No hypervitaminosis known.

Vitamin B₂

Name: Vitamin B₂ or riboflavin

Function in the body:

Riboflavin is part of the cofactors FMN and FAD which are important for electro transport in pyruvate, fatty acid and amino acid metabolism.

Store in the body: Not stored

Typical sources: Vegetables, eggs, meat, fish, yeast, milk and grains

RDA: 1.3 mg (1-4 mg)

Typical causes for deficiency:

Alcoholics have increased requirement of riboflavin. Deficiency may occur as part of complex vitamin B hypovitaminosis.

In hypothyroidism and adrenal failure is less riboflavin converted to its active form, thereby mimicking deficiency. Deficiency may also develop in therapy of psychiatric disorders when tricyclic antidepressants are used.

Hypovitaminosis condition:

Inflammation of GI tract, especially of the oral cavity (stomatitis, glossitis, cheilitis). Microcytic hypochromic anaemia may occur.

Hypervitaminosis condition: No hypervitaminosis known

Vitamin B₃

Name: Niacin, nicotinic acid or vitamin B₃

Function in the body:

Niacin is converted into NAD⁺ and NADP⁺ in the body, co-factors that are involved in many oxidation and reduction reductions. NADH transfers electrons to the mitochondrial electron transport chain while NADPH is involved in synthetic processes.

Store in the body: Not stored

Typical sources: Vegetables, eggs, meat, yeast, milk. Niacin is produced in limited amounts in the body from tryptophan.

RDA: 16 mg (20-25 mg)

Typical causes for deficiency:

Due to the body’s ability to synthesize some amounts of niacin does deficiency rarely develop unless there is both niacin and tryptophan (protein) deficiency. Chronic alcoholism with complex vitamin B hypovitaminosis. More frequent in places where maize (corn) is the major food group as maize has little niacin and tryptophan. Chronic diarrhoea. Increased requirement in rapid growth, pregnancy and lactation.

Hypovitaminosis condition:

The hypovitaminosis for niacin is called pellagra. The symptoms of pellagra can be summarized as the three (or four) D’s:

• dermatitis – photosensitivity, hyperkeratotic and hyperpigmented scaly skin
• diarrhoea – also glossitis, inflammation and atrophy of the GI mucosa
• dementia – due to lack of tryptophan and serotonin. Headache and insomnia too
• death

Hypervitaminosis condition:

Niacin is used as a serum cholesterol-lowering drug in pharmacological doses. Symptoms of hypervitaminosis are erythema and liver damage.

Vitamin B₅

Name: Vitamin B₅ or pantothenic acid

Function in the body: B₅ is the major component of coenzyme A (CoA). It’s essential for activation of fatty acids. It’s important in metabolism of carbs, proteins and fat.

Store in the body: No

Typical sources: Small quantities found in nearly every food (hence the name). Especially in egg and liver.

RDA: 5 mg

Typical causes for deficiency: Nothing special.

Hypovitaminosis condition:

Burning feet. Hypertension.

Hypervitaminosis condition: No hypervitaminosis.

Vitamin B₆

Name: Vitamin B₆ or pyridoxine

Function in the body:

Pyridoxine is the precursor for the cofactor PLP (pyridoxal phosphate). PLP is essential for more than 140 enzymes, accounting for a whopping 4% of all classified enzymes! It’s important in functions such as:

• Amino acid metabolism
• Conversion of tryptophan into niacin
• Dopamine and GABA production
• Homocysteine metabolism
• Porphyrin biosynthesis
• Immunological processes
• Gluconeogenesis, glycogenolysis

Store in the body: Not significant (2-6 weeks maximum)

Typical sources: Milk, eggs, fish, meat, yeast…

RDA: 1.3 mg (2 mg)

Typical causes for deficiency:

Complex vitamin B hypovitaminosis in chronic alcoholics. Pyridoxine is heat-sensitive, so overheated baby formulas may cause deficiency in the baby. Chronic diarrhoea. Pregnancy, lactation, children.

Isoniazid is an antibiotic for the treatment of tuberculosis. It’s a pyridoxine antagonist that deprives the body of pyridoxine. Pyridoxine should be supplemented during treatment with isoniazid.

Hypovitaminosis condition:

CNS convulsions may occur in infants due to decreased synthesis of GABA. Microcytic hypochromic anaemia due to the vitamin’s involvement in porphyrin synthesis. Atherosclerosis due to hyperhomocysteinaemia.

Hypervitaminosis condition:

No adverse hypervitaminosis symptoms are known, however high doses of pyridoxine can be used pharmacologically as an antiemetic.

Vitamin B₇

Name: Vitamin B₇ or biotin

Function in the body: Biotin itself is a cofactor in enzymes important for fatty acid synthesis and gluconeogenesis.

Store in the body: No

Typical sources: Synthesized by intestinal bacteria. Liver, egg.

RDA: 30 µg

Typical causes for deficiency: Occurs in persons consuming large amount of raw egg since the avidin of raw egg-white binds it, preventing its absorption.  Long term treatment with sulfonamides, that destroy intestinal bacterial flora may also cause deficiency symptoms.

Hypovitaminosis condition:

Dermatitis, hair loss.

Hypervitaminosis condition: No hypervitaminosis.

Vitamin B₉

Name: Folic acid, folate or vitamin B₉

Function in the body:

Folate is activated in the body to the coenzyme THF (tetrahydrofolate). This enzyme is essential for transport of methyl groups between molecules. It’s especially important for purine and pyrimidine synthesis, making it important for cell division.

It’s needed for amino acid metabolism and development of the foetal nervous system.

Store in the body: Not stored

Typical sources: Green plants (folium =green leaf), uncooked vegetables, liver, walnuts and chocolate(!)

RDA: 0.4 mg in healthy, 0.6 mg in pregnancy (0.5-2 mg)

Typical causes for deficiency:

Cooking damages folic acid, so consumption of only cooked vegetables can lead to deficiency. It’s deficient in complex vitamin B hypovitaminosis in chronic alcoholics. Chronic diarrhoea.

Methotrexate is a chemotherapeutic agent that inhibits the conversion of folate into THF. Patients on this therapy should receive folate supplements.

B₁₂ deficiency actually causes a virtual folate deficiency. B₁₂ is required for the conversion of folate from its inactive form to its active form. This is called the methyl-folate trap, as folate is “trapped” in the inactive methyl-folate form.

Hypovitaminosis condition:

Macrocytic hyperchromic anaemia may occur due to folate’s involvement in cell division. Pancytopaenia may also occur. GIT atrophy and inflammation and glossitis.

Neural tube closing defects like spina bifida occurs in infants whose mothers were deficient in folate during the pregnancy. For this reason are pregnant women advised to take 400 µg folate supplements daily.

Hypervitaminosis condition: No hypervitaminosis

Vitamin B₁₂

Name: Vitamin B₁₂, cyanocobalamin or cobalamin

Function in the body:

B₁₂ is a cofactor in the biochemical reaction that connects carbohydrate and fat metabolism. This is especially important for normal myelin sheath production.

It’s also needed for the regeneration of THF from methyl-THF to avoid the methyl-folate trap.

Store in the body: Several mg are stored in the liver. Enough for 3-6 years.

Typical sources: Meat, milk, egg

RDA: 2.4 µg (1-3 µg)

Typical causes for deficiency:

Vegans typically don’t consume any foods that contain B₁₂. Vegan food is often fortified with B₁₂ to combat this.

B₁₂ is absorbed as a complex with intrinsic factor in the terminal ileum. Diseases of the terminal ileum like Crohn’s disease impair B₁₂ absorption.

Chronic diarrhoea. Lack of intrinsic factor such as in pernicious anaemia or any other atrophy of the gastric mucosa.

The parasite Diphyllobothrium latum absorbs 80% of the hosts B₁₂ intake.

In liver disorders like cirrhosis are the B₁₂ stores decreased.

Hypovitaminosis condition:

Macrocytic hyperchromic anaemia. Pancytopaenia. GIT atrophy, inflammation and Hunter glossitis.

Demyelination of the dorsal column medial lemniscus in the spinal cords leads to ataxia and paraesthesia. This condition is called funicular myelosis.

Hypervitaminosis condition: No hypervitaminosis

Vitamin C

Name: Vitamin C, ascorbic acid or ascorbate

Function in the body:

Vitamin C is a cofactor for multiple reactions, like:

• Proline and lysine hydroxylase – essential for collagen synthesis
• Hydroxylation of cholesterol – essential for cholesterol metabolism
• Dopamine β-hydroxylase – essential for norepinephrine and epinephrine synthesis

It keeps ingested iron in the ferrous (Fe²⁺) form, which is more easily absorbed than the ferric (Fe³⁺). It’s needed for the transformation of cholesterol into bile acids and for proper function of the immune system as well.

Store in the body: Not stored

Typical sources: Broccoli, cauliflower, potatoes, red pepper, leafy greens, citrus fruits

RDA: 90 mg (70-100 mg)

Typical causes for deficiency:

Vitamin C is heat-sensitive, so cooking destroys it. Eating no fresh fruits or vegetables causes deficiency. Requirement is increased in pregnancy, during infections and lactation.

Hypovitaminosis condition:

The hypovitaminosis of vitamin C is called scurvy. The following are symptoms of scurvy:

• Vascular purpuras
• Gingival bleeding
• Loose teeth
• Prolonged wound healing
• Malaise and lethargy

Hypervitaminosis condition: Rare. Might cause kidney stones.