Vitamins, derived from the Latin word for life, are essential organic substances required in small quantities for optimal growth and overall well-being. Unlike other organic nutrients, vitamins don't act as sources of energy or building materials but rather facilitate these nutrients' utilization by the body. Vitamins are predominantly coenzymes, assisting enzymes in specific chemical actions, like the oxidation of glucose for energy involving B vitamins. Most vitamins are not produced in our bodies, necessitating their consumption through food or vitamin supplements. However, there are a few exceptions. Vitamin D is produced in the skin, and gut bacteria synthesize certain B vitamins and Vitamin K. Additionally, our body has the capacity to convert beta-carotene, a pigment in carrots and other foods, into Vitamin A. Such substances are referred to as provitamins. Although vitamins are present in all main food groups, no single food offers all the required vitamins, emphasizing the importance of a balanced diet. Originally, vitamins were named alphabetically based on the sequence of their discovery, a practice still widely used despite the existence of more chemically descriptive names. Vitamins are categorized into two: water-soluble and fat-soluble. Water-soluble vitamins like B-complex vitamins and Vitamin C are absorbed with water in the digestive tract, are scarcely stored in lean tissue, and excess amounts are eliminated through urine. Fat-soluble vitamins like A, D, E, and K, however, are absorbed with dietary lipids and stored in the body. Overconsumption of fat-soluble vitamins has been linked with toxicity. Metabolic processes that use oxygen generate some harmful free radicals, and vitamins like C, E, and A, along with the mineral selenium, partake in reactions to counteract these damaging free radicals. The process through which antioxidants work in the body remains not fully understood, but it's believed that they pass the destructive free electron from one molecule to another until a compound like glutathione absorbs it, and then excreted in urine. Foods like broccoli, cabbage, cauliflower, and Brussels sprouts are rich in vitamins A and C. Despite popular belief, consuming large amounts of vitamin supplements doesn't guarantee robust health and longevity. In fact, it can lead to adverse health effects, particularly in the case of fat-soluble vitamins.

Following are the clinical conditions, vitamin deficiencies, and vitamin toxicities

Vitamin A:

Vitamin A deficiency may lead to night blindness, which occurs when individuals have difficulty seeing in low-light conditions. Prolonged vitamin A deficiency can also cause xerophthalmia, a condition characterized by dryness and damage to the cornea, potentially leading to permanent blindness.

Overconsumption of vitamin A, particularly in the form of supplements, can result in a condition called hypervitaminosis A. Symptoms include nausea, vomiting, dizziness, hair loss, and even liver damage.

Vitamin D:

Vitamin D deficiency could weaken bones, leading to rickets in children and osteomalacia in adults. These conditions are characterized by bone pain, muscle weakness, and an increased risk of fractures.

Overconsumption of vitamin D can lead to hypervitaminosis D, which causes high calcium levels in the blood. This can cause nausea, vomiting, constipation, confusion, and even kidney damage.

Vitamin E:

Vitamin E deficiency is rare. It can occur in individuals having disorders causing malabsorption or certain genetic conditions. In severe deficiency cases, it can lead to neurological problems, such as muscle weakness, reduced coordination, and impaired vision.

Although rare, excessive intake of vitamin E through supplements can interfere with blood clotting, potentially leading to bleeding disorders.

Vitamin K:

A deficiency of vitamin K can impair blood clotting and result in a risk of profuse bleeding and bruising. Newborns are particularly susceptible to vitamin K deficiency, as they have limited stores at birth.

Overdosing on vitamin K through dietary sources is rare, but excessive intake of synthetic vitamin K supplements may possibly interfere with certain medications and may cause adverse effects.

B Complex Vitamins:

Deficiencies in B vitamins, including thiamine (B1), riboflavin (B2), niacin (B3), pyridoxine (B6), cobalamin (B12), and folic acid (B9), can result in various health issues.

Thiamine deficiency can cause beriberi, characterized by fatigue, muscle weakness, and nerve damage.

Riboflavin deficiency can cause mouth sores, cracked lips, and skin inflammation.

Niacin deficiency can cause pellagra, characterized by dermatitis, diarrhea, dementia, and even death if left untreated.

Pyridoxine deficiency can result in anemia, skin rashes, and neurological symptoms.

Cobalamin deficiency can caused by pernicious anemia, leading to fatigue, shortness of breath, and nerve problems.

In pregnant women, folic acid deficiency may cause neural tube defects in the developing fetus.

Excessive intake of B complex vitamins through supplements is generally considered safe, as these vitamins are water-soluble, so excess amounts are excreted in urine. However, extremely high doses can cause adverse effects.

Vitamin C:

An underconsumption of vitamin C can lead to scurvy, a condition characterized by fatigue, gum bleeding, poor wound healing, and joint pain.

Overconsumption of vitamin C is unlikely to cause significant harm, as excess amounts are excreted in urine. However, extremely high doses can lead to gastrointestinal disturbances, such as diarrhea and stomach cramps.