Vitamins play an important role in the body’s growth and development. There are thirteen essential vitamins found in the body, performing hundreds of different functions. These are Vitamin A, Vitamin C, Vitamin D, Vitamin E, Vitamin K and the B Vitamins which are thiamine, riboflavin, pantothenic acid, Vitamin B-6, biotin, folate and Vitamin B-12. They all contain their own unique properties and perform different services in the body. This article will provide an overview of all thirteen vitamins, what they do, and how to obtain them in your diet.

Vitamin A

Vitamin A is involved in immune function, vision, reproduction and cellular communication. It plays a critical part in vision as it makes up a part of the protein rhodopsin which absorbs light in the retinal receptors. It also supports the normal differentiation and functioning of conjunctival membranes and the cornea. Another important function of Vitamin A is the role it plays in cell growth and differentiation, playing an integral role in the formation and maintenance of the heart, lungs, kidneys and other organs.

There are two forms of Vitamin A that are available in the diet, preformed Vitamin A and pro-Vitamin A carotenoids. Preformed Vitamin A is found in animal sources including dairy, eggs, fish and meat(especially liver). Pro-Vitamin A carotenoids are alpha-carotene, beta-carotene and beta-crytoxanthin with beta-carotene being the most important by far. The body converts these plant pigments into Vitamin A. Other carotenoids that are found in food such as lycopene, lutein and zeaxanthin are beneficial but are not converted into Vitamin A.

Preformed Vitamin A concentrations are highest in liver and fish oil; eggs and dairy products are good sources as well. Dietary pro-Vitamin A comes from leafy greens, orange and yellow vegetables, tomato products, fruits, and some types of vegetable oil. The top food sources for providing Vitamin A in the typical American diet are dairy products, liver, fish and fortified cereals. The most common sources of pro-Vitamin A in the American diet are carrots, broccoli, cantaloupe and squash.

Vitamin A has been shown to be beneficial in many different circumstances. Observational studies have shown that higher intake of carotenoids in the form of fruits and vegetables are associated with a lower risk of lung cancer. This link is only with carotenoids that are obtained from the diet, there are no signs that supplemental Vitamin A provides a similar effect. Carotenoids also have anti-oxidant properties that can aid in the alleviation of the cumulative effects of oxidative stress that can lead to age-related macular degeneration. Finally, Vitamin A deficiency is a known risk factor for severe measles. The World Health Organization recommends administering a large oral dose of Vitamin A to children over the age of one when they contract measles in an area where Vitamin A deficiency is prevalent. Studies have shown that these high doses of Vitamin A lead to a reduced mortality rate in children for measles as well as pneumonia.

Vitamin C

Vitamin C is required for the biosynthesis of collagen, L-Carnitine and certain neurotransmitters; it is also involved in protein metabolism. Collagen is an essential component of connective tissue which helps aid the body’s healing process. Vitamin C is also a physiological antioxidant that has the ability to create other antioxidants in the body, this makes it an important part of immune function. It also improves the absorption of iron that is found in plants. Extended periods of Vitamin C restriction can lead to scurvy.

Fruits and vegetables are the best sources of Vitamin C. Citrus fruits, bell peppers, kiwis, broccoli, strawberries, brussels sprouts, cabbage, tomatoes, cauliflower, spinach and potatoes are all excellent sources of Vitamin C. Ascorbic acid(a synonym for Vitamin C) is water soluble and can be destroyed by heat which means certain methods of food preparation can significantly alter Vitamin C content. If eating food specifically for Vitamin C content the food should be consumed raw as often as possible and at peak freshness. If you do cook vegetables, steaming them minimizes vitamin loss when compared to other methods of preparation.

Vitamin C supplements are usually available in the form of ascorbic acid. Ascorbic acid has been show to have the same bioavailability(proportion of a substance that enters the circulation when introduced to the body and so is able to have an active effect) as that found in fruits and vegetables. Ascorbic acid base Vitamin C supplements have been proven to be effective and they are also relatively inexpensive making them among the most popular supplements overall.

Acute Vitamin C deficiency leads to scurvy. Symptoms of scurvy take around a month to begin appearing once Vitamin C intakes falls beneath 10mg/day. The first signs of scurvy are fatigue and swelling of the gums; once it progresses it leads to a litany of terrible effects which include joint pain due to the loss of connective tissue, loss of teeth and bleeding of the gums. If left untreated scurvy will ultimately lead to death. Scurvy was common among sailors who undertook long voyages until the 18th century when it was discovered that citrus fruit could fend it off. Scurvy is now extremely rare in developed countries.

Even though scurvy is now rare amongst developed populations, chronic Vitamin C deficiency is still relatively common. The populations who are most at risk of Vitamin C deficiency are smokers, infants who are fed boiled or evaporated milk, people with limited food variety and people who suffer from intestinal malabsorption problems.

Vitamin C may be helpful in both cancer protection as well as cancer treatment due to its ability to limit the formation of carcinogens. Case studies have shown an inverse relationship between dietary Vitamin C and many different prevalent forms of cancer. It also leads to a reduced risk of cardiovascular disease as the anti-oxidants found in Vitamin C lead to less oxidative damage as well as improved nitric oxide production and vasodilation which improves blood flow and reduces the buildup of plaque. Vitamin C also reduces the risk of Age Related Macular Degeneration and glaucoma, and may even shorten the duration of the common cold. There are minimal risks associated with excess Vitamin C intake due to its water solubility.

Vitamin D

Vitamin D is naturally present on very few foods but many foods are commonly fortified with it. It is also produced when ultraviolet rays hit the skin, which triggers Vitamin D synthesis in the body. Vitamin D’s main functions in the body are promoting calcium absorption in the gut and bone growth and repair. Vitamin D also modulates cell growth, neuromuscular and immune function and reduces inflammation.

Salmon, tuna, swordfish and fish liver oils are the best dietary sources of Vitamin D. There are also small amounts present in cheese, eggs and beef liver. Fortified foods are responsible for most of the dietary Vitamin D consumed in the United States. Nearly all milk is fortified with it, as well as many breakfast cereals and some orange juices.

Most people get at least some of their Vitamin D from sun exposure. Under normal sun conditions most people are able to get enough Vitamin D in 30 minutes twice a week of unprotected sun exposure when the sun is at its peak between 10 a.m and 3 p.m. Though sun exposure is vital when it comes to getting adequate Vitamin D, ultraviolet radiation is a carcinogen that is responsible for skin cancer and melanoma.

Rickets is the disease that is most commonly associated with Vitamin D deficiency. The disease is characterized by the failure of bone tissue to properly materialize which causes soft bones and skeletal deformities. The government mandated milk to be fortified with Vitamin D in the 1930s in order to combat rickets. While there are still documented cases they have become exceedingly rare.

There are many different groups that are at risk of insufficient Vitamin D intake. Breast fed infants who don’t receive supplements will have low Vitamin D as there is very little available in breast milk. Older people are also at an elevated risk because their skin does not synthesize Vitamin D as efficiently; they also tend to get less sun exposure than younger people. People with darker skin also don’t receive as much Vitamin D from the sun due to lower levels of melanin, which is responsible for skin pigment. Those who are obese or have had gastric bypass surgery also may need more Vitamin D than others, as it is absorbed through the intestine; part of which is no longer part of the digestive system after gastric bypass surgery.

Adequate Vitamin D levels are linked to many benefits. It helps the body with the absorption of calcium which can lower the risk of osteoporosis. Studies also indicate that Vitamin D supplementation can lead to a lower incidence of cancer among individuals who are of average weight. There are also indications that Vitamin D plays many roles in the prevention and treatment of many different conditions but more studies are needed.

Vitamin E

Vitamin E occurs naturally in many foods, is fortified into others and is also available as a supplement. It is a fat soluble vitamin, and has many antioxidant properties. Antioxidants protect cells from free radicals-molecules that contain an unshared electron. Free radicals damage cells and contribute to cardiovascular disease and cancer, they are caused by environmental factors like cigarette smoke, air pollution and ultraviolet radiation from the sun. Vitamin E helps to neutralize the their damaging effects.

The best food sources of Vitamin E are sunflower seeds, almonds, peanuts, peanut butter, hazelnuts and vegetable oils. There are smaller amounts of Vitamin E available in kale, spinach and other leafy greens.

Acute Vitamin E deficiency is very rare in healthy adults. Those who are at the highest risk are people who have problems absorbing fat into the digestive tract as Vitamin E is fat soluble. Severe Vitamin E deficiency causes problems with the immune system and nerve damage.

The primary benefits of Vitamin E are derived from its role as an antioxidant, its aiding in the anti-inflammatory process, and its ability to enhance immune function. It plays an important role in the prevention and treatment of coronary heart disease, cancer, eye disorders and cognitive decline.

There is a large amount of evidence that Vitamin E can prevent or delay the onset of coronary heart disease. Vitamin E inhibits the oxidation of LDL or “bad cholesterol”, and it may help prevent blood clots that can cause heart attacks due to its role in improving blood flow. A large, multi year study found that rates of heart disease were 30% to 40% lower amongst those with the highest intakes of Vitamin E which came primarily in the form of supplements.

Antioxidants like those found in Vitamin E protect cells from the damage caused by free radicals, this damage can lead to the development of cancer. It may also protect against the formation of carcinogens in the stomach deriving from nitrites in the diet. Vitamin E’s role in the enhancing of the immune system also helps to deter the development of cancer.

Vitamin E may also be used in the prevention and treatment of aged related macular degeneration and glaucoma, diseases that are caused by the cumulative effects of oxidative stress. Antioxidant intake helps to alleviate and even reverse this accumulated stress.

Cumulative free radical damage to neurons contributes to neurodegenerative diseases like Alzheimer’s. This means that increased consumption of Vitamin E may lead to slower mental deterioration, but more studies are needed.

There are no known ill effects from consuming large amounts of dietary Vitamin E, however, too much supplemental Vitamin E has been shown to cause hermorrhaging in animal studies.

Vitamin K

Vitamin K is a fat soluble vitamin found primarily in leafy green vegetables. It is required for the synthesis of proteins involved in homeostasis(blood clotting) and with bone metabolism. Vitamin K is present in the liver, brain, heart, pancreas as well as in the bones. The body retains little Vitamin K as it is metabolized much more quickly than other fat soluble vitamins.

Major food sources of Vitamin K include vegetables, vegetable oils and some fruits. Foods with the highest concentration of Vitamin K are collard greens, turnip greens, spinach, kale, broccoli, carrot juice, soybeans, pomegranate juice and pine nuts. Most U.S. diets contain sufficient Vitamin K, it is also widely available in supplement form.

Vitamin K deficiency is very rare in adults, it is found most often in people with malabsorption disorders. It can also be found in people who have received gastric bypass surgery. Infants who don’t receive Vitamin K supplementation are also at risk of deficiency as there is little Vitamin K in breast milk.

Vitamin K plays an important role in the treatment and prevention of osteoporosis. Osteoporosis is a disorder characterized by fragile and porous bones, and it affects more than 10 million Americans-80% of which are women. Consumption of calcium and Vitamin D in childhood and adolescence maximizes bone mass and density which can reduce the risk of osteoporosis later in life. Clinical trials have shown that Vitamin K supplementation improves bone strength and density and increases vertebral height in post menopausal women. Vitamin K doses are used as treatment for osteoporosis in Japan, and in Europe it is legal to claim that “a cause and effect relationship has been established between the dietary intake of Vitamin K and the maintenance of normal bone”. The FDA does not yet allow the same sort of claim in the United States.

Vascular calcification reduces elasticity of the arteries and aorta and is a major risk factor for coronary heart disease. Observational studies have shown that dietary intake of Vitamin K is inversely associated with coronary calcification.

Vitamin K has a low potential for toxicity and there are no known levels at which intake has been shown to have deleterious effects.

Vitamin B1 (Thiamine)

Vitamin B1, also called thiamine or thiamin, is one of the water soluble B vitamins. It is naturally present in some foods, added to others and available as a supplement. It plays a critical role in energy metabolism and the growth, development and function of cells. Thiamine is stored in the liver in very small amounts and has a very short half life, making a continuous supply necessary.

In the United States many breads, cereals and infant formulas are fortified with thiamine. Due to its water solubility, the cooking process can significantly alter and reduce the thiamine content of foods. Foods with the highest thiamine content include pork chops, trout, black beans, mussels, brown rice, acorn squash, orange juice and bottom round.

Thiamine deficiency can be caused by both insufficient intake as well as from lower absorption or higher secretion rates than normal. People at the highest risk of thiamine deficiency include people with alcohol dependence, older adults, people with HIV and diabetes as well as people who have undergone bariatric surgery. Studies have shown that up to 80% of people with alcohol dependency have thiamine deficiency, as alcohol both reduces absorption as well as depletes thiamine stores in the liver.

Thiamine deficiency is related to many severe health problems. Wernicke-Korsakoff syndrome is an extremely severe neuropsychiatric disease that is caused by depleted thiamine levels due to chronic alcoholism. Studies have suggested that supplemental thiamine can aid in the treatment of diabetes. Thiamine deficiency has also been linked to heart disease and Alzheimer’s.

There are no known harmful side effects from ingesting too much thiamine, as thiamine’s water solubility allows excess to be excreted through urine. People who take diuretics may need to take supplemental thiamine in order to offset the loss of thiamine.

Vitamin B2 (Riboflavin)

Vitamin B2, or riboflavin, is another of the water soluble B vitamins. It is found in some foods, added to others and is available as a dietary supplement. It plays a major role in energy production, cellular function, growth, and development, and in the metabolism of fats. Riboflavin also helps to maintain normal levels of amino acids in the blood. Riboflavin is absorbed in the small intestine, and small amounts are stored in the liver, heart and kidneys.

Riboflavin is present in many foods, those with the highest levels include beef liver, fortified breakfast cereals, yogurt, milk, beef steak, almonds, clams, eggs, chicken breast and salmon. As is the case with all B vitamins, riboflavin’s water solubility means that foods can lose a large amount of the vitamin during the cooking process.

Riboflavin deficiency is very rare in developed countries. The groups at the highest risk of riboflavin deficiency are vegan and vegetarian athletes, as exercise produces stress on the parts of the body that metabolize riboflavin and it is difficult to consume enough of the vitamin without consuming animal products. Pregnant and breastfeeding women who eat little or no meat are also at risk of riboflavin deficiency for the same reason, as well as passing on some of the riboflavin stores that they have to their infants through breastfeeding.

Studies have found evidence of riboflavin supplementation having a positive influence on reducing the frequency of migraines in those who suffer from them. There is also some evidence that riboflavin supplementation can also reduce their severity. There is limited scientific data on the relationship between riboflavin intake and cancer prevention, but experts have theorized that it may help to alleviate damage to DNA that is caused by carcinogens.

Riboflavin is not known to be toxic at any levels due to its water solubility and the body’s inability to absorb exceptionally high levels. Even though there are no known side effects, it is still not a good idea to consume it in excessive amounts.

Vitamin B5 (Pantothenic acid)

Vitamin B5, also known as pantothenic acid, is an essential nutrient that is found naturally in some foods, added to others and also available as a supplement. It is water soluble like all B vitamins; its main role in the body is in the synthesis of fatty acids. Pantothenic acid is absorbed by the intestines and moved around the body directly through the bloodstream.

Nearly all plant and animal dietary sources contain at least some pantothenic acid. Like all B vitamins, pantothenic acid is water soluble and different cooking techniques can radically alter the amount that is conveyed. The best dietary sources of pantothenic acid include beef liver, shitake mushrooms, sunflower seeds, avocado, white mushrooms, potatoes, chicken breast, broccoli, chickpeas and brown rice. Most people with a typical diet in developed countries consume adequate amounts of pantothenic acid. Pantothenic acid deficiency is extraordinarily rare, it is essentially found only in those who suffer from extreme malnutrition.

Studies have shown that pantothenic acid can be used to lower LDL, or bad cholesterol. This is due to its role as a synthesizer of triglycerides. Definitive data is not yet available, as more and larger studies are necessary to determine causation.

There are no serious known side effects caused by excessive intake of pantothenic acid, although diarrhea and other gastrointestinal issues are possible.

Vitamin B6

Vitamin B6 is found in many foods, fortified in others and widely available as a supplement. It is water soluble along with the rest of the B vitamin family. Vitamin B6 is responsible for many different functions in the body including cognitive development, immune function, the formation of hemoglobin and in protein metabolism.

Vitamin B6 is found in many different types of food; some of the best sources are chickpeas, salmon, tuna, beef livers, chicken breast, turkey, bananas, tomato sauce and potatoes. Vitamin B6, along with the other B vitamins, are among the most popular supplements on the market.

Deficiency of Vitamin B6 on its own is rare, it is almost always accompanied by the deficiency of other complex B vitamins. Vitamin B6 deficiency can lead to anemia, dermatitis, depression and to diminished immune function. It can be caused by diseases of the kidneys as well as other diseases that are characterized by malabsorption issues. People with alcohol dependence are also likely to have low concentrations of Vitamin B6.

It is theorized that Vitamin B6 supplementation can lead to a lower risk of heart disease and stroke, however, there are not enough studies to confirm this hypothesis. More research is also needed to determine whether Vitamin B6 plays a role in the slowing of cognitive decline in older adults. There is stronger evidence that Vitamin B6 can help to alleviate the symptoms of premenstrual syndrome as well as the nausea and vomiting known as “morning sickness” during the early stages of pregnancy.

There are some side effects that can accompany excessively large intakes of Vitamin B6. These range from relatively minor symptoms such as heartburn and nausea all the way up to complete loss of bodily movements. Sensitivity to light as well as skin lesions can also occur, although none of these symptoms are expected except after large supplemental levels have been consumed over the course of several months, and there are no known side effects to consuming too much dietary Vitamin B6.

Vitamin B7 (Biotin)

Vitamin B7, also known as biotin or Vitamin H, is an essential nutrient that is part of the water soluble B vitamin family. It occurs naturally in some foods, usually bound to protein, and is also available is supplements. Its key roles in the body are in the regulation of genes and n cell signaling.

Biotin is found naturally in may different foods, although preparation techniques and freshness have a large impact on the amount that is contained. Foods with the highest biotin content include eggs, beef livers, pork chops, hamburger, salmon, sweet potatoes, spinach, broccoli and sunflower seeds. Biotin is available in several different supplement forms, all of which have a 100% absorption rate.

There are no known reports of individuals suffering from severe biotin deficiency while eating an average diet. There are a few groups of people at risk of biotin deficiency and they include those who are at risk of deficiency with all of the B vitamin family; they include pregnant and breastfeeding women and those with chronic alcoholism.

Biotin deficiency can lead to hair loss, cracked and brittle nails and rashes. Studies have hinted that biotin supplementation may help to strengthen hair and nails, but there have been no large scale studies published as of this time.

There are no known negative health consequences from excessive intake of biotin, although high levels of biotin supplementation can interfere with lab results and lead to incorrect diagnoses if other symptoms are present.

Vitamin B9 (Folate)

Vitamin B9, known more commonly as folate, and when it is fully oxidized as folic acid, is a water soluble member of the family of B vitamins. It occurs naturally in some foods, is fortified in many others and is available as a supplement. Folate plays an integral role in the synthesis of both DNA and RNA as well as in the metabolism of amino acids.

Folate is present across a large spectrum of foods, and since 1998 in the United States it has been mandated to be added to enriched breads, flours, cereals and most grain products. The foods with the best concentrations of folate include spinach, asparagus, black eyed peas, beef livers, brussels sprouts, mustard and turnip greens, kidney beans and avocadoes. Many countries in the Western Hemisphere require folate to be added to enriched grain products. It is also available in a wide range of supplement forms both on its own as well as in multivitamins; it is a key component of both prenatal as well as children’s multivitamins.

Folate deficiency is rare in isolation, it usually occurs in conjunction with deficiency of other essential vitamins. Pregnant women are among those at the highest risk of folate deficiency due to folate’s role in the formation of DNA and RNA, the recommended daily value of folate consumption during pregnancy is higher for this reason. Other groups at risk of insufficient folate are those with alcohol use disorder and those with malabsorption disorders.

Observational data suggest that there is a correlation between low levels of folate consumed during pregnancy and the risk of having a child with a diagnosis on the Autism Spectrum Disorder. Research has also suggested an inverse relationship between consumption of larger levels of folate and the development of many types of cancer. This may be due to folate’s function as a metabolizer of carbon, which would help to eliminate carcinogens from the body. Studies have also suggested that folic acid may have something of a preventive affect when it comes to dementia, Alzheimer’s and overall cognitive decline, although more research is needed to prove causation.

There are some negative consequences that are related to excessive intake of folate. It has been linked to problems with immune functioning as well possibly leading to accelerated cognitive decline in older adults when taken at high levels. There have also been studies that indicate if women exceed healthy doses while pregnant, their children will have lower cognitive scores on average by the time they are five years old.

Vitamin B12

Vitamin B12, also called cobalamin because it contains the mineral cobalt, is a water soluble member of the B vitamin family. It is naturally present primarily in foods from animal sources, fortified in other foods and is available as a supplement as well as in prescription medications. Vitamin B12 plays an important role in many functions in the body including DNA synthesis, formation of red blood cells and aiding in neurological functioning.

Vitamin B12 occurs naturally only in animal products, but many breakfast cereals as well as yeasts are fortified with it. Foods with the best sources of Vitamin B12 are clams, beef livers, tuna, salmon, trout, haddock, sirloin, hamburger, eggs, cheese, yogurt and milk. Vitamin B12 is available both as a supplement and as a prescription medication, and is available in many different forms. Some of these form include tablets, lozenges, nasal sprays as well as injection drugs and gels.

Most people with average diets consume sufficient quantities of Vitamin B12. B12 deficiency results in anemia, fatigue, loss of appetite, weight loss and constipation. Other symptoms that can occur are difficulty with motor skills, depression and memory problems. Deficiency is usually treated with injections, as one of the major causes of B12 deficiency is malabsorption and the injections bypass this problem.

Groups at the highest risk of Vitamin B12 deficiency are older adults, people with anemia, people with malabsorption disorders and vegetarians and vegans. Vegetarians and vegans are the most likely group to get inadequate Vitamin B12 if they do not use supplements, as it occurs naturally only in animal products.

Vitamin B12 is hypothesized to be helpful in both the prevention and treatment of both coronary heart disease as well as in dementia and Alzheimer’s, but available studies are not conclusive enough to state this claim definitively. Vitamin B12 is also regularly promoted as an athletic performance and energy booster since it plays a central role in energy metabolism. It has not been determined that B12 supplementation has this effect when the person taking it already receives adequate levels.

Vitamin B12 has a low potential for toxicity, and there is no known limit at which consuming too much can have deleterious effects.