Role of Vitamins in Diet

Role of Vitamins in Diet

While carbohydrates, proteins, and fats are considered important macronutrients in our diet, vitamins are micronutrients that play a significant role in metabolism and overall human health.1 Although current research is inconclusive about their role in improving metabolic and cardiovascular (ie, heart and blood-vessel related) health, vitamins are essential for numerous cellular reactions and should be adequately consumed as a part of a healthy diet.2,3 Vitamins are categorized into essential water-soluble vitamins (vitamins B and C) and fat-soluble vitamins (vitamins A, E, D, and K).1



Vitamin A is a fat-soluble vitamin necessary for vision, skin, bone, and immunity.1 There are often found in eggs, milk, and liver as well as fresh fruits and vegetables that are red, orange, or yellow. Deficiency in vitamin A can be dangerous in children and is associated with higher mortality rates, increased risk of infections, and decreased growth. Too much vitamin A can also be toxic, leading to liver injury, jaundice, and portal hypertension (ie, high blood pressure in the venous system connected to the liver).4 


Vitamin B describes several types of water-soluble vitamins essential for normal growth and metabolism: vitamins B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate), B12 (cyanocobalamin).

Vitamin B1 (Thiamine) – Vitamin B1 is essential for carbohydrate and protein metabolism and can be found in enriched and whole grains, pork, and legumes.1 Deficiency in vitamin B1 can be caused by chronic alcoholism and can lead to extreme weight loss, confusion, weakness in the muscles, and enlargement of the heart. 

Vitamin B2 (Riboflavin) – Vitamin B2 is needed in biochemical reaction called the redox reaction.1 It is found in enriched and whole grains, leafy vegetables, dairy products, and beef. Deficiency in vitamin B2 can lead to weakness, sore throat, and inflammations of the skin, tongue, and the oral mucosa.

Vitamin B3 (Niacin) – Vitamin B3 is essential in certain metabolic reactions and can be found in enriched and whole grains, eggs, dairy products, and meat.1 Deficiency in vitamin B3 is called pellagra, which is characterized by rash in sun-exposed areas, vomiting, diarrhea, tiredness, depression, and headache. 

Vitamin B5 (Pantothenic Acid) – Vitamin B5 is important for the metabolism of fat and can be found in various types of foods.1 Deficiency in vitamin B5 can lead to tiredness, sleep disturbances, gastrointestinal discomforts, and hypoglycemia.

Vitamin B6 (Pyridoxine) – Vitamin B6 is essential for the metabolism of protein and carbohydrates and can be found in various types of foods.1 Although deficiency in B6 is rare, it can lead to confusion, dermatitis (inflammation of the skin) of the scalp, and abnormalities in the red blood cell (called microcytic anemia).

Vitamin B7 (Biotin) – Vitamin B7 plays an important role in certain biochemical reactions in the body and can be found in various types of foods including whole grains, egg yolks, and soybeans.1 Deficiency is rare and can occur in people with genetic defects or in those who eat raw eggs (as proteins in raw eggs inhibit B7 absorption). People can experience thinning of hair, dermatitis, tiredness, and hallucinations with B7 deficiency.

Vitamin B9 (Folate) – Vitamin B9 is essential for protein metabolism and synthesis of DNA and RNA.1 It is found in fortified and enriched grains, green leafy vegetables, and legumes. Vitamin B9 is especially important for women of childbearing age as deficiency in B9 during early pregnancy can cause neural tube defects (eg, anencephaly and spina bifida). In addition, deficiency in vitamin B9 can result in certain types of anemia characterized by very large red blood cells. 

Vitamin B12 (Cobalamin) – Vitamin B12 is essential in certain metabolic reactions in the body and can only be found in animal products or in products fortified with B12.1 Deficiency in vitamin B12 causes pernicious anemia (decrease in red blood cells), often caused by autoimmune disorders or stomach inflammations that inhibit the absorption of B12. Vitamin B12 deficiency can also cause neural tube defects and impair neurological function.


Vitamin C is a water-soluble vitamin with essential roles in enzymatic reactions in the body with antioxidant effects.1 It can be found in citrus fruits, green vegetables, tomatoes, and potatoes. Deficiency in vitamin C causes what is known as scurvy. Although rare, it can cause bruising, joint pain, fatigue, inflammation of the gums, and bleedings. 


Vitamin D is a fat-soluble vitamin that plays an important role in regulating calcium metabolism and bone health.1 Vitamin D can be found in fish oils, but is also unique from other vitamins in that humans can synthesize it with adequate exposure to sunlight. Deficiency causes rickets (lack of mineralization of bone) in children that result in bowing of long bones of the legs and growth impairment.

Vitamin E

Vitamin E is a fat-soluble vitamin and acts as an antioxidant that protects cells from oxidative stress, regulates immune function, maintains endothelial cell integrity, and balances normal coagulation.1 Vitamin E can be found in whole grains, nuts, green leafy vegetables, and certain vegetable oils (eg, canola, olive oil, sunflower, safflower). Although rare, deficiency in vitamin E can cause tissue and cellular damages, hemolytic anemia (where red blood cells are destroyed faster than they are produced), and neurologic abnormalities.


Vitamin K is a fat-soluble vitamin that plays an important role in normal coagulation.1 Green leafy vegetables as well as canola oil and soybean oil are great sources of vitamin K. Vitamin K deficiency is uncommon in adults, but newborns are at a higher risk as their intestines lack vitamin K-synthesizing bacteria and milk is often low in vitamin K. Vitamin K shots are often given to infants to prevent vitamin K deficiency bleeding that can cause neural and liver damages.



1. Morris A, Mohiuddin S. Biochemistry, Nutrients. StatPearls. Published online May 1, 2023. Accessed June 16, 2023.
2. Aguilera-Méndez A, Boone-Villa D, Nieto-Aguilar R, Villafaña-Rauda S, Molina AS, Sobrevilla JV. Role of Vitamins in the Metabolic Syndrome and Cardiovascular Disease. Pflugers Arch - Eur J Physiol. 2022;474(1):117-140. doi:10.1007/s00424-021-02619-x
3. Martini LA, Catania AS, Ferreira SRG. Role of Vitamins and Minerals in Prevention and Management of Type 2 Diabetes Mellitus. Nutr Rev. 2010;68(6):341-354. doi:10.1111/j.1753-4887.2010.00296.x
4. Vitamin A. In: LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. National Institute of Diabetes and Digestive and Kidney Diseases; 2012. Accessed June 16, 2023.



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