Vitamins: A Crash Course

We all know we need vitamins, but have you ever really thought about what they actually do? There’s a commercial on TV right now that says vitamins are the fuel for your cells – but that’s not quite right. So what is the role of vitamins in your body?

What are Vitamins?

Vitamins are an essential part of your body’s everyday functions. They can act as coenzymes that help with chemical reactions, assist in growth and development, and help to maintain the health of your tissues and immune system.

There are 13 essential vitamins: Thiamine (B1), Riboflavin (B2), Niacin (B3), Pantothenic Acid (B5), Pyridoxine (B6), Biotin (B7), Folate (B9), Cobalamin (B12), Vitamin C, Vitamin A, Vitamin D, Vitamin E, and Vitamin K.

Water-Soluble Versus Fat-Soluble

Vitamins are broken into two categories: water-soluble and fat-soluble.

Water-soluble vitamins need water to be dissolved and absorbed by your body. They are not stored in large amounts so do not typically cause toxicity, or poisonous effects. Water-soluble vitamins can be easily damaged by cooking, exposure to air, and exposure to light.

Fat-soluble vitamins need fat to be dissolved and absorbed by the body. People on a low-fat diet are at an increased risk of being deficient in these vitamins. Fat-soluble vitamins are stored in the liver and body fat, so toxicity can occur if you eat too much.

How Much Do You Need?

The amount of vitamins you need each day depends on your age, sex, and any medical conditions you may have. The RDA, or Recommended Daily Allowance, is used to show how much the average person needs of each nutrient. AI, or Adequate Intake, is used when a Recommended Daily Allowance is not available due to a lack or research or knowledge of the vitamin.

Deficiencies and Toxicity

Deficiencies can occur when you don’t eat enough fruits, vegetables, whole grains, and other healthy whole foods. You may also develop deficiencies if have a restrictive diet like low-fat or vegan, or take certain medications like antacids. Many people also become less able to absorb vitamins as they age.

Toxicity is usually seen in people who take supplements. It is difficult to get too many vitamins from food alone. It is important not to take more than the Recommended Daily Allowance of any vitamin unless instructed to do so by medical professional.

Water Soluble Vitamins


  • Also known as: Vitamin B1
  • Function: Thiamine plays a role in the metabolism of carbohydrates and assists with muscle contraction and nerve signaling.
  • Sources: pork, sunflower seeds, legumes, whole grains, eggs, mushrooms
  • RDA: 1.2 mg for men, 1.1 mg for women
  • Deficiency: Low levels of Thiamine is rare in the general population but can be seen in alcoholics. It can cause conditions like Beriberi, which affects the cardiovascular system or the nervous system, or Wernicke Korsakoff, which causes brain damage.
  • Toxicity: Not seen.


  • Also known as: Vitamin B2
  • Function: Riboflavin helps create energy from food, works alongside Vitamin B6, Folate, and Iron, and assists with the creation of red blood cells.
  • Sources: beef, dark meat chicken, eggs, dark leafy greens, milk, nuts, salmon
  • RDA: 1.3 mg for men, 1.1 mg for women
  • Deficiency: Low levels of riboflavin can lead to inflammation of the mouth and tongue, cracks at the corners of the mouth, sores, headache, anemia, and fatigue.
  • Toxicity: Not seen.


  • Also known as: Vitamin B3
  • Function: Niacin helps create energy from food, assists with the breakdown of protein, carbohydrates, fat, and alcohol, and helps the body create cholesterol and fatty acids.
  • Sources: chicken, beef, fish, peanuts, legumes, eggs
  • RDA: 16 mg for men, 14 mg for women
  • Deficiency: Low Niacin can cause a condition called Pellagra, which has symptoms that include dry skin, bright red tongue, vomiting, fatigue, depression, and if left untreated, death.
  • Toxicity: High levels of Niacin does not cause toxicity, but too much can lead to increased blood sugar levels, liver damage, flushing, and skin rash.
  • Pharmacological Use: can be used for people with high cholesterol levels to lower blood triglycerides, cholesterol, and HDL. Side effects include flushing, itching, and tingling skin.

Pantothenic Acid

  • Also known as: Vitamin B5
  • Function: Pantothenic Acid assists with the breakdown of carbohydrates, protein, and alcohol and helps with the creation of bile, hormones, and fatty acids.
  • Sources: meat, milk, mushrooms, peanuts, egg yolks, broccoli
  • AI: 5 mg for men and women
  • Deficiency: Pantothenic Acid deficiency is very rare. It can cause tingling in the feet and muscle pain.
  • Toxicity: Not seen.


  • Also known as: Vitamin B6
  • Function: Pyridoxine is used for creation of red blood cells, maintaining good brain health, creating antibodies, maintaining good nerve health, and breaking down proteins.
  • Sources: meat, fish, chicken, carrots, potatoes, spinach, avocado
  • RDA: 1.3 mg for men and women
  • Deficiency: Low levels of Pyridoxine leads to dry lips, irritability, depression, confusion, and tingling in hands and feet.
  • Toxicity: Unlike other water-soluble vitamins, Pyridoxine toxicitycan occur and causes nerve damage.
  • Pharmacological Use: Pyridoxine can be used for the treatment of carpal tunnel syndrome, premenstrual syndrome, and nausea during pregnancy.


  • Also known as: Vitamin B7
  • Function: Biotin helps with the breakdown of amino acids (the building blocks of protein) for energy and the creation of fatty acids.
  • Sources: whole grains, nuts, legumes, liver, egg yolk
  • RDA: 30 mcg for men and women
  • Deficiency: Low Biotin levels are rarely seen. Deficiency can be seen in people who eat raw eggs. Low levels can cause skin rash, hair loss, convulsions, and impaired growth.
  • Toxicity: Not seen.


  • Also known as: Vitamin B9 or Folic Acid (the synthetic form)
  • Function: Folate helps form neurotransmitters like serotonin and dopamine, assists with the creation of DNA, and works with Vitamin B12 and Vitamin C to help create red blood cells.
  • Sources: liver, legumes, green leafy vegetables, avocado, oranges
  • RDA: 400 mcg for men and women
  • Deficiency: Folate deficiency is commonly seen in alcoholics and can lead to lowered immune system, poor growth, and ulcers in the mouth and stomach. Low folate can also lead to a type of anemia called Megaloblastic Anemia.
  • Toxicity: Folate toxicity is not seen, but too much folate can hide the symptoms of a Vitamin B12 deficiency.


  • Also known as: Vitamin B12
  • Function: Cobalamin assists with the breakdown of fatty acids, helps create of red blood cells and maintains central nervous system functioning.
  • Sources: animal products like meat, milk, and eggs
  • RDA: 2.4 mg for men and women
  • Deficiency: Low Cobalamincan cause nerve degeneration, difficulty walking, and weakness. Deficiency can also cause a type of anemia called Pernicious Anemia. Cobalamin deficiency is commonly seen in vegans, the elderly, people with Inflammatory Bowel Disease, and people taking acid reducers.
  • Toxicity: Not seen.

Vitamin C

  • Also known as: Ascorbic Acid
  • Function: Vitamin C acts as an antioxidant to eliminate harmful free radicals. It also helps synthesize collagen, assists with the absorption of iron, and helps with wound healing and immune function.
  • Sources: citrus, green vegetables, kiwi, strawberries, brussels sprouts
  • RDA: 90 mg for men, 75 mg for women
  • Deficiency: Low Vitamin C can lead to easy bruising, fatigue, poor wound healing, fractures, bleeding gums. Extreme Vitamin C deficiency causes a condition called Scurvy.
  • Toxicity: Vitamin C toxicity is not seen, but too much can lead to an upset stomach and diarrhea.
  • Pharmacological use: Mega-doses of Vitamin C have been shown to have little to no effect on the common cold.

Fat Soluble Vitamins

Vitamin A

  • Also known as: Retinol (active form) or Beta Carotene (precursor used to form retinol)
  • Function: Vitamin E assists in the maintenance of healthy teeth, skin, and tissue, and is important for vision health.
  • Sources:
    • Retinol – liver, fish, eggs, butter
    • Beta Carotene – carrots, sweet potatoes, mango, peaches
  • RDA: 900 mcg in men, 700 mcg in women
  • Deficiency: Low levels of Vitamin E causes dry eye, night blindness leading to full blindness, and follicular hyperkeratosis (pimple-like bumps on the skin).
  • Toxicity: Too much Vitamin E causes GI upset, headaches, dizziness, liver damage, and loss of appetite.
  • Pharmacological Use: Vitamin E can be used in the treatment of severe acne and psoriasis.

Vitamin D

  • Also known as: Cholecalciferol
  • Function: Vitamin D assists with the absorption of calcium and phosphorous and helps the immune system function properly.
  • Sources: fatty fish, fortified milk, UV light
  • RDA: 600 IU
  • Deficiency: Too little Vitamin D leads to an increased risk of autoimmune disease. Low levels can also lead to Rickets in children (bowed legs, short height) and Osteoporosis in adults (porous bones that easily fracture).
  • Toxicity: Extra Vitamin D intake causes too much calcium to be absorbed. This can lead to calcium buildup in the heart and lungs, kidney stones, and disorientation.
  • Special Recommendations: Receptors under your skin create Vitamin D using UV rays from sunlight. Vitamin D is a common deficiency because of how much time we spend indoors and the use of sunscreen. Many people have trouble getting enough of this vitamin from food or sun exposure and may need to talk with their doctor or dietitian about supplementation, especially during the winter.

Vitamin E

  • Also known as: Tocopherol
  • Function: Vitamin E works as an antioxidant, assists Vitamin K in the creation of red blood cells, and helps maintain the immune system.
  • Sources: plant and vegetable oils, nuts, seeds, spinach, broccoli
  • RDA: 15 mg for men and women
  • Deficiency: Too little Vitamin E leads to a lowered immune system, poor nervous system functioning, and a type of anemia called Hemolytic Anemia.
  • Toxicity: High levels of Vitamin Elowers the function of Vitamin K, leading to hemorrhage (severe bleeding).

Vitamin K

  • Also known as: Phylloquinone or Menaquinone
  • Function: Vitamin K is important in the creation of blood clots.
  • Sources: Vitamin K is synthesized by bacteria in your colon; it can also be found in green leafy vegetables, broccoli, green beans, liver
  • RDA: 120 mcg for men, 90 mcg for women
  • Deficiency: Too little vitamin K causes hemorrhage and bruising.
  • Toxicity: Vitamin K toxicity is rare. Extra Vitamin K is easily gotten rid of in the urine and doesn’t build up in the body.

A Note About Supplements

The best place to get your vitamins is from food. Vitamins do not work on their own – they need other vitamins, minerals, phytochemicals, and other important nutrients to do their job. This is called food synergy. When you get your vitamins from food, they naturally come with the other nutrients that allow them to work properly. Supplements do not have the benefit of food synergy.

Be careful when choosing supplements. The Food and Drug Administration does not regulate supplements to make sure they are safe. Look for a brand that is GMP certified, meaning they follow good manufacturing processes. Also look for brands that have independent lab testing done on their products. This lets you know that the supplement contains what it’s supposed to.

Always talk with your doctor or dietitian before starting any supplements, especially if you are on any prescription or over-the-counter medication. Vitamin supplements can interact with many medications and can lead to deficiencies or toxicity.

Originally published on

Published by Kelli Yates, RDN, LD, CLT

Kelli Yates, RDN, LD, CLT is a Registered Dietitian Nutritionist specializing in holistic migraine management and fellow migraineur!

Leave a Reply