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Monday Article #44: Vitamin B complex: What is it and why is it so important?

Vitamin is defined as “any of a group of natural substances that are necessary in small amounts for the growth and good health of the body,” where deficiencies will lead to various diseases [1]. Vitamins can be divided into two main groups, namely fat-soluble vitamins (A, D, E, K) and water-soluble vitamins (B-complex and C).

Of all the vitamins listed above, perhaps most people find vitamin B-complex the most confusing as the complex consists of eight different types of water-soluble vitamins, which include thiamin (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folic acid (B9), and cobalamin (B12). Vitamins Bs can be found in a wide variety of foods and play a role in various processes in the body.

Figure 1. An illustration of vitamin supplement [2].

Thiamin (B1), riboflavin (B2), and niacin (B3) all play a role in energy metabolism, to release energy from foods [3]. Thiamin (vitamin B1) acts as a cofactor for carboxylation and transferases reactions needed for carbohydrate metabolism. For example, the conversion of pyruvate into acetyl-CoA by pyruvate dehydrogenase requires vitamin B1 as a cofactor. On the other hand, riboflavin (vitamin B2) acts as a cofactor as FAD (Flavin Adenine Dinucleotide), which is required by many reactions of the metabolic pathways, including the conversion of succinate to fumarate in the Krebs cycle and oxidation of acyl-CoA into trans-△2-Enoyl-CoA in fatty acid oxidation, both of which are heavily involved in the generation of energy from food sources. Niacin (vitamin B3) acts as a cofactor as NAD+ and NADP+, which are both also required for many reactions in metabolism. For example, conversion of glyceraldehyde-3-phosphate to glycerate-1,3-bisphosphate in the glycolytic pathway, formation of oxaloacetate from malate for the synthesis of glucose, as well as the synthesis of fatty acids. Since most grain products or cereals are fortified with these vitamins, deficiency is usually not an issue in normal individuals. However, conditions such as alcoholism or a low-calorie diet may lead to deficiencies of vitamins B1, B2, B3, causing the development of diseases such as Beri-beri, glossitis, and pellagra respectively.

Figure 2. An illustration of thiamine-dependent reactions in metabolic pathways [4].

Pantothenic acid (vitamin B5) is a component of Coenzyme A, which functions in the transfer of acyl group. Hence, it is involved in the formation of hormones, production of energy, and metabolism of carbohydrates, fats and protein from food. Pantothenic acid can be found in foods such as eggs, liver, whole grains, and legumes. It is also synthesised by intestinal bacteria. Therefore, due to its wide availability in a variety of foods, deficiency of vitamin B5 is rare and no known problems are associated with overconsumption.

Pyridoxal phosphate, which is a coenzyme required for many reactions such as transamination reactions that are crucial for protein metabolism and red blood cell formation in the body, is the active form of pyridoxine or vitamin B6 [5]. Meats, whole grains, legumes, and green leafy vegetables are all common sources of vitamin B6. Breast milk and formulas also contain sufficient vitamin B6 for infants. Due to its crucial roles in the body, deficiency of pyridoxine may lead to dermatitis, anaemia, and mental confusion in infants.

Figure 3. (A) The structure of Coenzyme A with the pantothenic acid circled [6].

(B) Function of pyridoxal phosphate in transamination reactions [7].

Vitamins B7, also known as biotin, acts as a cofactor for all carboxylation processes in the body, for the synthesis of glucose and fat [8]. Biotin can also be seen in many hair products in the market since it is believed to promote production of keratin in hair and increase the rate of hair follicle growth. Similar to other B vitamins, vitamin B7 can be found in foods such as liver, eggs, kidney, cereals, and most fresh vegetables. Furthermore, biotin is also synthesised by intestinal bacteria. Hence, biotin deficiency is relatively uncommon in normal individuals. Nevertheless, deficiency of this important nutrient may lead to symptoms such as nausea, vomiting, anorexia, dermatitis, heart abnormalities, and anaemia.

Figure 4. Image of vitamin B7 dietary supplement for drops for hair health [9].

A relatively commonly known vitamin B, folic acid (B9), is crucial for promoting formation of red blood cells, synthesis of nucleic acids, and lowering the risk of neural tube defects [3]. Therefore, women who are intending to conceive soon will usually be advised to take folic acid supplements to support the rapid cell division and nucleic acid synthesis after the initial implantation of the blastocyst (blastocyst forms five to six days after fertilisation of the egg by the sperm). Besides that, folate also helps to manage homocysteine levels to prevent its accumulation and hence reduce the risk of coronary heart diseases. If not removed rapidly, homocysteine will lead to aggregation of low-density lipoproteins (LDLs) which deposits on inner linings of arteries, resulting in atherosclerosis. Sources of vitamin B9 are similar to other B vitamins, however, not all grain products have been fortified with folate, so do read the nutritional label to check if folic acid has been added.

Finally, cobalamin or vitamin B12, also assists in the synthesis of nucleic acids, production of normal red blood cells, conversion of homocysteine to other products, as well as maintenance of the nervous system [3]. Since vitamin B12 can only be found in foods of animal origins, such as shellfish, liver and kidneys, vegetarians and infants of vegan mothers are often at risk of deficiency. Due to its vital role in the human body, deficiency of this vitamin will lead to megaloblastic anaemia, nerve degeneration and neurological disorders.

Figure. Vitamin B9 and B12 in 1-carbon metabolism [10].

As discussed above, all eight types of vitamin B play crucial roles in the human body in various processes and reactions. While the different roles played by each type is complicated and not necessary to memorise, it is important to try to prevent extreme restriction of caloric intake and have a well-balanced diet to avoid deficiencies.

[1] Cambridge Dictionary. (n.d.). Vitamin. Retrieved from

[2] Healthline. (n.d.). B-Complex Vitamins: Benefits, Side Effects, and Dosage. Retrieved from

[3] Bellows, L., Moore, R., Anderson, J. and Young, L. (2012) ‘Water-soluble vitamins: B-complex and vitamin C’, Food and nutrition series. Health; no. 9.312. [Online] Available at: (Accessed: 1 January 2023).

[4] Yartsev, A. (2015). Thiamine deficiency as a cause of lactic acidosis. Retrieved from

[5] National Center for Biotechnology Information. (2023). PubChem Compound Summary for CID 1051, Pyridoxal phosphate. Retrieved from

[6] Nutrition Flexbook. (n.d.). 10.6 Pantothenic Acid. Retrieved from

[7] Engelking, L.R. (2015) ‘Biotin and Pyridoxine’, Textbook of Veterinary Physiological Chemistry (Third Edition), 42, pp. 271-275. [Online] DOI: 10.1016/B978-0-12-391909-0.50042-6 (Accessed: 3 January 2023).

[8] Tong, L. (2013) ‘Structure and function of biotin-dependent carboxylases’, Cellular and Molecular Life Sciences, 70(5), pp.863-891. [Online] DOI: 10.1007/s00018-012-1096-0 (Accessed: 3 January 2023).

[9] Fruugo. (n.d.). Life-Flo Biotin Drops. Retrieved from

[10] Finkelstein, J.L., Layden, A.J. and Stover, P.J. (2015) ‘Vitamin B-12 and perinatal health’, Advances in Nutrition, 6(5), pp.552-563. [Online] DOI: 10.3945/an.115.008201 (Accessed: 3 January 2023).


Article by Phoebe Tee

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