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Unlocking the Vitamins: Understanding Their Functions and Roles in Health

Vitamins are essential micronutrients that are required to facilitate regular bodily functions, such as maintaining healthy teeth, skin, brain functions, and bones. 

In contrast to macronutrients, such as fats, proteins, and carbohydrates, vitamins are required in minuscule quantities and are usually derived unknowingly from food sources. 

In this article, we’ll discuss the different categories of vitamins and their mechanisms in great detail. 

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Overview of Vitamins

Grouped in 2 categories, 13 vitamins are essential in different amounts for our body to perform the necessary functions. These categories include:

  • Water-soluble vitamins

  • Fat-soluble vitamins 

They’re quite different in functionality, and our body has different ways to retain and excrete them. 

Water-Soluble Vitamins

Although all the vitamins are required in adequate amounts for your body to function, water-soluble vitamins are washed out quite easily and need to be replenished more frequently. 

These vitamins, upon introduction into the digestive system, are mostly absorbed in the small intestine and released into the bloodstream. These vitamins, namely Vitamins C and B-Vitamins, don’t need to go through a lipid-incorporation process to be transported. 

Easy delivery of these vitamins also makes them more susceptible to elimination and any excess amount of these vitamins is excreted through the kidneys and urine.

Vitamin C (Ascorbic Acid)

Found naturally in most citrus foods and veggies, Vitamin C or ascorbic acid is a water-soluble vitamin that works as a cofactor for enzymes to grow collagen, a fibrous protein in connective tissues of the nervous, immune, and various other systems. It also promotes better wound healing and strengthening of the immune system.

As a cofactor, Vitamin C maintains enzyme-bound metals in their reduced forms and helps enzymes carry out the hydroxylation of proline and lysine, which helps in collagen growth and antioxidant activities.

The main sources of Vitamin C are: 

  •  Citrus fruits

  • Spinach

  • Brocolli

  • Potatoes

  • Tomatoes

  • Cabbage

  • Cauliflower

  • Dairy and meat

Being a water-soluble vitamin, Vitamin C needs to be replenished almost every day to maintain a normal level. The recommended dietary allowance (RDA) of Vitamin C for women is 75 milligrams and 90 milligrams for males, with the upper limit being 2000 milligrams. Smokers are advised to add 35 milligrams of additional Vitamin C to their diet to reinforce antioxidation. 

Signs of Vitamin C deficiency include scurvy, a common disease among sailors between the 16th and 18th centuries, identified by weakness, gum disease, and skin hemorrhage. As many as two million sailors had this disease during this period. 

Vitamin B1 (Thiamin)

Also known as Thiamin, Vitamin B helps cells transform carbohydrates into energy. Vitamin B1 acts as a coenzyme to several enzymes involved in the Krebs cycle, which processes food into energy. Thiamin specifically helps metabolize carbohydrates, fats, and amino acids to produce Adenosine triphosphate (ATP), the energy currency of the body. 

Thiamin plays an essential role in the synthesis of neurotransmitters as well—allowing nerve cells to communicate with each other. Furthermore. Vitamin B1 also maintains better muscle function, heart health, and cognitive function.

However, our body can’t synthesize Vitamin B1 and the only source of it is our food sources, such as: 

  • Milk

  • Egg

  • Lean meats

  • Dried beans

  • Whole grains

  • Flour

  • Peas

Similar to other water-soluble vitamins, Vitamin B1 also needs to be replaced daily. While the upper limit of Thiamin is still unknown, a minimum of 1.1 mg of Thiamin for females and 1.3 mg of Thiamin for males is recommended. Not getting enough Vitamin B1 may cause beriberi, a disease that causes nerve, heart, and brain abnormalities.

Vitamin B2 (Riboflavin)

Identified by its greenish-yellow color, Riboflavin or Vitamin B2 supports an array of enzymes and bodily functions. In addition to supporting other vitamins in breaking down carbohydrates, fats, and proteins for energy, Vitamin B2 helps in DNA and RNA synthesis. It helps in cell growth and regeneration as well. 

Riboflavin is also an essential component of rhodopsin, a pigment found in the retina of the eye—helping you see in dim light. Furthermore, Vitamin B2 plays a critical role in producing red blood cells and serotonin. 

While gut bacteria synthesize a limited amount of Vitamin B2, that’s insufficient and needs dietary backup for replenishment. A few good sources of Vitamin B2 are: 

  • Eggs

  • Milk and yogurt

  • Meat and poultry

  • Fish and shellfish

  • Leafy green vegetables

  • Whole grains

  • Nuts and seeds

Riboflavin has an RDA of 1.1 mg for females and 1.3 mg for males, with the upper limit still unknown. If you’re pregnant or breastfeeding, 1.4 mg and 1.6 mg of Riboflavin, respectively, are recommended.

It also needs to be replenished regularly to sustain its functions. Vitamin B2 deficiency, aka ariboflavinosis, may cause stomatitis. A disease that causes chapped lips, inflammation of the mouth, red tongue, and hair loss. Your eyes can become itchy and sensitive to light. It may also cause anemia. 

Vitamin B3 (Niacin)

One of the most essential and demanded B-Vitamins, Niacin or Vitamin B3 associates itself as a coenzyme in the Krebs Cycle that converts food into energy. Similar to other B-Vitamins that we discussed, niacin also breaks down carbohydrates, fats, and amino acids to generate ATP—keeping your body energized. 

Vitamin B3 arguably reduces the risks of cardiovascular diseases by raising “good cholesterol (HDL)” levels. However, Niacin therapies in higher dosages can cause significant health issues, such as skin flushing, itching, gout, and liver damage. Consult your physician before considering such treatments.

With more than 400 enzymes requiring nicotinamide adenine dinucleotide (NAD, the metabolically active form of Niacin) to catalyze reactions, Niacin is required in large amounts, which can be obtained from: 

  • Soymilk

  • Beef liver

  • Avocado

  • Fish

  • Lean meats

  • Nuts

  • Potato

  • Poultry

  • Enriched breads

The recommended dietary allowance (RDA) for Vitamin B3 for adult females is 14 mg, which goes up to 16 mg for the male population. An upper limit of 35 mg has been imposed to prevent overdosing. Moreover, being water-soluble, Niacin needs to be replaced regularly. 

Deficiency of Niacin causes Pellagra, which is characterized by skin lesions and gastrointestinal disturbances with abnormal sensitization of the skin to sunlight. 

Skin lesions set out as severe sunburns that develop into rough, scaly flare-ups. Gastrointestinal symptoms include diarrhea and neurological issues like dementia and mental aberrations may develop in later stages. 

Vitamin B6 (Pyridoxine)

Responsible for over 100 enzymes involved in carbohydrate, protein, and fat metabolism, Vitamin B6 helps your body in energy production and perform various other bodily functions. It’s crucial in the synthesis of serotonin, dopamine, GABA, and a few other neurotransmitters, which help maintain mood, sleep, and cognitive functions. 

It’s also responsible for maintaining blood glucose levels and producing hemoglobin and white blood cells. Furthermore, Vitamin B6 supports hormone regulation and conversion of tryptophan to Vitamin B3. 

The major sources of Vitamin B6 include: 

  • Banana

  • Dried beans

  • Beef and pork

  • Whole grains and cereals

  • Tuna and Salmon

  • Poultry

As its major function involves protein metabolism, you require more Vitamin B6 with increasing protein intake. However, the general recommendation for adult males and females (age 19 - 50) is 1.3 mg. It’s advised to increase the supply of Vitamin B6 after age 50 to a 1.5 to 1.7 mg range. The upper RDA limit for Pyridoxine is 100 mg. Excess consumption of Vitamin B6 may cause nerve damage in the arms and legs. 

While rare in the US, deficiency of Vitamin B6 may cause metabolic disorders and mental depression. Dermatitis and convulsions may also be observed in extreme cases.  

Vitamin B12

The largest and most complex vitamin containing a metallic ion, Vitamin B12 supports folic acid in DNA synthesis and plays a pivotal part in the production of red blood cells. It participates in the conversion of food to ATP as two coenzymes: methylcobalamin and 5-deoxyadenosylcoblamin.

B12 also contributes to the overall safety and effectiveness of the nervous system by synthesizing fatty acids in the myelin sheath in the nerve cells. This insulating layer protects the nerve cells, propagates electrical impulses, and maintains the clarity of the impulse message. 

The primary sources of Vitamin B12 in our daily diet are: 

  • Meat

  • Fortified food

  • Milk and dairy

  • Animal liver

  • Poultry

  • Eggs

  • Shellfish

However, we require a very miniscule amount of Vitamin B12 to maintain its functions. 2.4 micrograms of daily B12 intake is adequate for both adult males and females. Hence, at least in the US, Pernicious anemia (caused by Vitamin B12) is rare and often is caused by other underlying issues. The symptoms include: 

  • Fatigue

  • Rapid heartbeat

  • Unsteady gait

  • Neurological issues

  • Memory loss

Vitamin B12 sourced from animals is absorbed more quickly. Followers of a strictly vegan diet (Also devoid of dairy products) may need to supplement the requirements through additional means. 

Vitamin B5 (Pantothenic acid)

A key component of Coenzyme A, Vitamin B5 or Pantothenic acid helps enzymes to break down or build fatty acids. Similar to other B vitamins, B5 also contributes to the energy production cycle by converting fats, carbohydrates, and proteins to ATP. Being efficient in breaking down fat, pantothenic acid is potentially perceived as an effective measure against people with higher cholesterol and dyslipidemia. 

Vitamin B5 is also involved in the production of adrenal hormones, such as cortisol and sex hormones, helping your body perform normal reproductive functions and cope with stress. Furthermore, Vitamin B5 participates in the synthesis of neurotransmitters like acetylcholine and improves cognitive function and mood regulation. 

Our gut bacteria can produce some pantothenic acid, but the primary source of Vitamin B5 remains in our dietary intake. Almost all plant and animal food sources contain pantothenic acid, but the major ones include: 

  • Organ meats like liver and kidney. 

  • Beef

  • Chicken breast

  • Fortified cereals 

  • Milk and dairy products

  • Potatoes

  • Eggs

  • Oats

  • Mushrooms

Although an upper limit of Vitamin B5 hasn’t been reported yet, a daily dosage of 5 mg is sufficient for adult individuals, both males and females. 

Deficiency symptoms usually include: 

  • Headache

  • Irritability

  • Nausea

  • Muscle cramps

  • Disturbed sleep

  • Stress and anxiety

Given that every living cell contains pantothenic acid, usually the necessary amount of the same is received through our regular diet unless malnutrition is involved. 

Vitamin B7 (Biotin)

Popular by the name Biotin and popularized through the promise of stopping hair loss, Vitamin B7 primarily acts as coenzymes to break down carbohydrates, metabolize amino acids, and synthesize fatty acids to produce energy. The claim of hair loss prevention, however, comes from its involvement in the production of keratin, the essential protein to maintain hair health. 

The other functions of biotin involve DNA synthesis and regulating neurotransmitters like serotonin—which maintains mood, sleep cycle, and a few cognitive responses. It also helps control blood sugar and cholesterol mechanisms. 

The primary sources of Biotin include: 

  • Beef liver

  • Salmon

  • Avocados

  • Nuts

  • Seeds

  • Potatoes

  • Milk

  • Poultry 

The daily adequate intake (AI) for Biotin for both males and females is 30 micrograms, with no safe limit discovered as of yet. While our varied diet can fulfill the Biotin requirements, alcoholism can block absorption and cause Vitamin B7 deficiency. The signs of Biotin deficiency are: 

  • Thinning hair

  • Brittle nails

  • Scaly skin

Biotin supplements often claim to solve hair loss issues, but most research involving Biotin supplements above the adequate requirements has been proven to be inconclusive.  

Vitamin B9 (Folic acid)

Absorbed better in the form of folic acid and naturally found in many foods, Vitamin B9 is one of the most essential B vitamins that is involved in the formation of DNA and RNA. Protein metabolism and elimination of excess homocysteine also are considered key functions of Vitamin B9. Homocysteine is an amino acid containing sulfur that can increase the risk factor of coronary atherosclerosis and ultimately cardiovascular disease. 

B9 also participates in red blood cell formation and the formation of several neurotransmitters, including dopamine and serotonin—regulating your mood, sleep, and cognitive functions. Besides, it plays an important role in maintaining immune system function and wound healing. 

While the primary source of Vitamin B9 for us is veggies and beans, supplements are more effective in replenishing the same for their folic acid content. Here are a few natural sources of Vitamin B9: 

  • Leafy vegetables

  • Peanuts

  • Beans

  • Fresh fruits

  • Liver

  • Whole grains

  • Eggs

  • Aquatic food, fish

The upper limit of safe consumption of Vitamin B9 or folic acid is 1000 micrograms, while the recommended daily allowance for adult males and females is 400 micrograms. Consequently, pregnant women are only advised to take folic acid supplements on a regular basis. 

Taking a higher amount of folic acid (more than 1000 mcg) daily has the potential to mask Vitamin B12 deficiency. Which can cause irreversible damage to the nervous system and cognitive functions. 

Signs of Vitamin B9 deficiency include: 

  • Megaloblastic anemia (a condition that produces less red blood cells)

  • Weakness

  • Fatigue

  • Hair loss

  • Mouth sores

  • Shortness of breath

Vitamin B9 deficiency is extremely rare and happens only because of other situations, such as alcoholism, pregnancy, gene variants (MTHFR), and malnutrition. 

Fat-Soluble Vitamins

In contrast to their water-soluble counterparts, fat-soluble vitamins can’t be absorbed in the watery environment of the intestine and need a special hitchhiking mechanism to be carried to the target tissues. 

The mechanism itself is pretty complex and discussing it is beyond the scope of this article, still, we’ll try to give you a nice outline. 

The journey of fat-soluble vitamins, such as A, D, E, and K, starts with the introduction of dietary fat. Bile from the liver and enzymes from the pancreas break down the fats into smaller globules called micelles—which allow the fat-soluble vitamins to hitch a ride and escape the watery environment. Micelles contain both fat and water-soluble components. 

Once the package is received inside the intestinal epithelial cells, it’s ‘repackaged” into lipoprotein particles called chylomicrons, surrounding the vitamin packages with phospholipids and protein coats—making them water-soluble and ready to transport.

Upon further travel through the lymphatic system, chylomicrons encounter lipoprotein lipase attached to the lining of the blood vessels. The fat and cholesterol are released directly into the surrounding tissues for energy and storage, while the remaining fat-soluble vitamins are taken up by the liver for further processing and distribution. 

The liver extracts specific vitamins and binds them to carrier protein for transport to tissues. These carrier proteins are: 

  • Vitamin A binds to retinol-binding protein

  • Vitamin D to vitamin D-binding protein

  • Vitamin E to alpha-tocopherol transfer protein

  • Vitamin K to vitamin K-dependent protein S.

While storage potential may vary, excess fat-soluble vitamins are stored in the liver and used when required. 

Vitamin A

Also known as Retinol, Vitamin A is a fat-soluble alcohol required to maintain proper vision and immune function directly. Vitamin A (Retinol) is converted into retinaldehyde, an essential component of rhodopsin present in the retina—transforming light into electrical signals. 

Retinol is converted through retinal pigment epithelial (RPE) cells located in the retina of your eye, where the enzyme RDH oxidizes Retinol and generates retinaldehyde.   

In addition to maintaining epithelial tissues, Vitamin A is also essential for regulating embryonic development and growth. Moreover, sperm production and egg development are supported by Retinoic acid. 

While Vitamin A is readily available in fatty fish and fish-liver oils, it’s not present in plants. However, several pigment classes found in plants can be converted to Vitamin A in our body. For instance, beta-carotene or provitamin A is found in carrots. Including the plants, major sources of Vitamin A are:

  • Fatty fish

  • Fish-liver oil

  • Milk and milk products

  • Egg yolk

  • Dark-colored fruits

Vitamin A is required in a very small amount in the human body. The daily recommended amount for adult men is 900 micrograms, while it’s 700 micrograms for women. Vitamin A toxicity, also called hypervitaminosis A, is caused by a high intake of Vitamin A (over 15000 micrograms) over several months.

Vitamin A deficiency, however rare in developed countries, causes retinal and epithelial issues. 

Common symptoms include night blindness, teary eyes, swollen eyelids, and dry mucous membranes of the mouth, urinary passages, and throat. 

Vitamin D

Often referred to as “sunshine vitamin”, Vitamin D is a family of nutrients responsible for calcium metabolism. While it’s primarily formed by the ultraviolet radiation (sunlight) of sterols present in the skin, food sources also replenish our bodily need for Vitamin D groups. In fact, excess sunlight alone can’t cause Vitamin D toxicity. 

Two major forms of Vitamin D are present as cholesterol compounds. Vitamin D2 (calciferol) is found in plants and Vitamin D3 (cholecalciferol) is found in animal tissues. All forms of Vitamin D contribute to bone health and prevent osteoporosis in the elderly population. It also promotes better cell growth and developed muscle function for improved mobility and performance. 

Apart from sunlight, the best sources of Vitamin D for us are: 

  • Fatty fish, such as salmon, herring, and mackerel

  • Cod liver oil

  • Fortified cereals

  • Milk and dairy products

With older adults requiring a higher dosage, regular dietary allowance recommendations for Vitamin D are similar for both males and females. 15 micrograms of dietary Vitamin D for adults between 19-70 years of age and 20 micrograms for elderly individuals (71+) are considered adequate in most cases. 

Vitamin D deficiency often causes rickets, osteomalacia, and osteoporosis. Caused by inadequate Vitamin D intake, a low serum calcium concentration in the blood triggers the secretion of parathormone. It releases bone calcium to restore serum calcium levels—causing bones to lose their integrity.  

Vitamin D toxicity, on the other hand, is caused mainly by excessive dietary supplements and is called hypervitaminosis D. The condition often leads to the accumulation of calcium phosphate throughout the body—particularly in the kidneys. The symptoms may include vomiting, nausea, and loss of appetite.

Vitamin E

Acting as your body’s antioxidant, Vitamin E shields cells from peroxides and other free radicals originating from essential metabolic processes and external sources like pollution and cigarette smoking. These free radicals potentially can steal electrons from the cells—making them weaker (like rust)—in order to stabilize themselves.

Vitamin E, rich in hydrogen atoms, acts as a sacrificial shield, donating the hydrogen atoms to the free radicals and protecting the cells. This process often causes a chain reaction and forces Vitamin E to steal atoms from other molecules (often Vitamin C) to regenerate itself and keep working. 

The primary sources of Vitamin E are: 

  • Avocado

  • Dark green leafy vegetables

  • Sunflower oil

  • Mango

  • Papaya

  • Seeds and nuts

  • Wheat germ

For both males and females, 15 mg of daily Vitamin E is considered sufficient, with 1000 mg being the safe limit. Vitamin E deficiency often causes ataxia, impaired vision, muscle loss, and reproductive issues. Vitamin E toxicity, however, can result in thinner blood, diarrhea, and fatigue. 

Vitamin K

Derived from the Danish word "Koagulation", Vitamin K is a group of naphthoquinone compounds that synthesize several blood clotting factors, including prothrombin and factors VII, IX, and X. Without sufficient Vitamin K, clotting can be impaired and may cause excessive bleeding and death. 

It also plays critical roles in bone and heart health. For example. Vitamin K activates a protein called osteocalcin, which helps build and maintain strong bones. Furthermore, it prevents calcification in arteries and reduces the risk of heart disease. 

While the majority of Vitamin K is replenished by gut bacteria, prime sources of the same include: 

  • Cereals

  • Cauliflower

  • Cabbage

  • Leafy vegetables

  • Fish

  • Beef liver

  • Eggs

Consequently, regular dietary allowance also stays at diminutive levels at 90 micrograms for females and 120 micrograms for males with the toxic upper limit still unknown. 

Although quite rare in humans, deficiency of Vitamin K may lead to an increased blood clotting time. Newborn infants are often administered with Vitamin K to supplement the absence of the gut bacteria.

The Bottom Line

Vitamins are key to many essential metabolic processes. From facilitating reactions to literally saving us from bleeding out, vitamins are crucial for maintaining optimal health. Understanding how these micronutrients work and the specific roles each one plays is essential for a comprehensive approach to nutrition.

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