Vitamins A-Z

There are 14 vitamins that the body requires on a regular basis. While some can be synthesized (such as vitamin D from sunlight), for proper physical and mental health function, most have to be consumed through diet or supplementation.

Uses

Vitamins are compounds that are necessary for a wide range of biological functions. They play a role in nearly everything the body does. Each vitamin is responsible for a specific set of functions, and deficiency in a particular type can lead to disease.

Types of vitamins

Here is a list of some of the most common vitamins you should get from your diet our through supplementation.

Vitamin A

The belief that carrots are good for your eyesight stems from the fact that they're high in vitamin A, and that A vitamins are necessary for proper retina functioning. But vitamin A is also needed by the immune system and for cell growth. A deficiency can cause skin problems, loss of color vision, nyctalopia (night blindness), and even general blindness (keratomalacia).^[1]

B Vitamins

While the other vitamins are very straightforward, vitamin B gets a little complicated. It's made up of a range of numbered subcategories (B1, B2, etc.), each of which is actually a distinct vitamin with unique functions. This happened because the entire complex of B vitamins was once thought to be a singular entity. It was later discovered that each component was chemically distinct. It eventaully became standard practice to refer to every component as a number.

To further confuse things, these vitamin B subcategories are sometimes referred to as a different letter, for example, "B7" is sometimes called "vitamin H" and "B9" is also known as "vitamin M."

Products that contain "B-complex" typically have several separate B vitamins, which are preferable when looking for general supplementation. They are typically marketed towards their energy production characteristics.

Below, each B vitamin is listed in more detail:

Vitamin C

Vitamin C is used throughout the body. It's needed to synthesize collagen, carnitine, tyrosine, and neurotransmitters. It's also the most common antioxidant in a regular diet, is a major fuel source for immune system cells, and is an antihistamine. The most colorful and well-known disease caused by a C deficiency is scurvy, though cases are rare these days thanks to the vitamin's ubiquity in diet.

Modern cases of scurvy are generally only seem in individuals who have bulimia or alcoholism. Less severe early signs of deficiency include fatigue, depression, bleeding gums, easy bruising, and joint pain.^[11]

Vitamin D

For years, vitamin D was thought to play a role in supporting bone health, but the evidence isn't entirely conclusive. The vitamin is defined more by what happens when you're deficient: rickets and osteoporosis.

As with scurvy, however, diet and supplementation have largely eliminated rickets outside of developing countries. Also known as the sunshine vitamin, vitamin D is the only vitamin that isn't essential in diet, as the skin can synthesize it from sun exposure.^[12]

Vitamin E

Vitamin E works in tandem with vitamin C as one of the most common and potent antioxidants. It's also a critical component in muscle growth, gene expression, and neurological function. Deficiency can cause mobility or coordination problems, muscle weakness or failure, nerve disease, impaired immune function, retinal damage, and the death of red blood cells.^[13]

Vitamin K

There are actually two types of vitamin K: K1 and K2. Unlike B-complex, they're generally regarded as one entity as the colon can synthesize K2 from K1. Vitamin K is most critical in blood coagulation. Lack of the nutrient can lead to uncontrolled bleeding, osteoporosis, and heart disease.^[14]

Recommended dosage

All of those "for men," "for women," and "silver" vitamin formulations aren't just marketing fluff. The primary determinants for your RDA are age and gender.

The above table, with data provided by the IOM, lists each vitamin with corresponding RDA (recommended daily allowance) and UL (tolerated upper limit) for male and female adults. Always consult with your pediatrician before giving children or infants a vitamin. Also, women who are pregnant or lactacting should discuss their vitamin needs with her health care provider.

Forms

Vitamin supplements are available individually, in packs of individual pills for each type of vitamin, or with many or all of the daily vitamins, amalgamated into one pill called a multivitamin.

Hard pills

In recent years, a number of studies suggesting that taking the hard pill form of vitamins may lead to incomplete absorption has created a surge in popularity of alternate forms.^[15,16] To promote absorption, consume your vitamins in these forms:

Vitamins that are mixed with a powdered food can also promote absorption.Gelcaps

• Gummies
• Powders
• Liquids

Synthetic vitamins

Most vitamin supplements are formulated synthetically. Unless you're consuming your vitamin from dietary sources (food vs. capsules or powders), it's likely your vitamins were made in a lab. This is not necessarily a bad thing — your synthetic vitamin C pill is the same the C in your orange. One benefit of getting your vitamins from food is that they provide additional micronutrients and plant-based phytonutrients that are not found in synthetic multivitamins.Synthetic vitamins are also sometimes added to beverages in the manufacturing process. Vitaminwater is a popular example. Today, several vitamin beverages, such as Odwalla, are marketed for the purpose of providing a concentration of vitamins from fruits and vegetables.

Toxicity

All vitamins have a potential upper limit (UL), after which they can have toxic effects. Fat-soluble vitamins are the only ones that you really need to be concerned with. Vitamins A, D, E, and K differ from water-soluble vitamins in that they are stored in body fat for later use, and will accumulate to toxic levels over time, especially if you take more than your RDA, or have a health condition that prevents your liver from properly processing nutrients.

Water-soluble vitamins (B-complex and vitamin C) still have toxic thresholds, but to reach them they generally must be taken in massive single doses that would not be encountered in nature (or even in supplementation).

Toxicity details

Depending on the type of vitamin you take, toxicity symptoms can range from irritating to dangerous.

Vitamin K toxicity

Of the fat-soluble vitamins, you don't need to worry about vitamin K. There's no recommended UL as there's never been a known case of toxicity due to overdose.^[17]

Vitamin A toxicity

Vitamin A's average toxic dose (which should not be confused with the tolerable upper limit) is 120,000 IU (international units) per day, but liver damage has occurred at doses of 15,000 IU per day (toxicity is exacerbated by poor overall diet and alcohol consumption).

Vitamin E toxicity

Vitamin E's upper recommended limit is 1,000mg (1,500 IU) per day for adults. While not as dangerous as A or D, at toxic levels the primary concern is that an overdose can prevent blood from clotting. Other symptoms may include blotchy skin, decreased production of thyroid hormones and increased triglycerides.^[19]

Vitamin D and toxicity

The actual limits of toxicity of vitamin D (and resulting symptoms) are still somewhat in dispute among experts, but the IOM has set the toxicity threshold at either 300,000 IU in a 24-hour period, or over 10,000 IU per day for three or more consecutive months. Unfortunately, the symptoms are vague and overlap with many other common maladies, such as nausea, reduced appetite, excessive thirst or urination, gastrointestinal pain or disorders, fatigue, muscle weakness, and confusion. A simple test can determine if vitamin D is the culprit by checking your blood calcium levels — if they're too high, you'll have to cut down your intake for several months and possibly take a prescribed corticosteroid.^[20]

Children and pregnancy

Toxicity can occur in children beginning at 1,500 IU/kg of body weight. Potential symptoms are many and varied. The most serious are hair loss, muscle weakness, weakened bones (leading to risk of fractures), weight loss, and anemia. Vitamin A toxicity can also damage the fetus during pregnancy.^[18]

Food sources

Most foods contain at least one of the essential vitamins in some amount. Many processed foods are also fortified with synthetic vitamins as a way to be more attractive to consumers.

A well-balanced diet is the best way to meet all of your vitamin needs, but supplementation can help when that isn't possible, or when your nutrient needs exceed normal standards due to high-level training.

Considerations

Because vitamins are defined by the FDA as dietary supplements, the agency's monitoring responsibility is limited to removing illegal substances from the market rather than verifying quality or content.^[21] Independent reviews that are accompanied by testing from unbiased labs are generally your most reliable source of information on supplement standards and safety.WarningsVitamins and supplements are drawn from varying sources, and potency and quality may vary. While the science is not entirely conclusive on the subject, synthetic vitamins sometimes haven't fared as well in studies as those from natural sources, in terms of uptake and absorption.^{[22, 23]}Beverages like Vitaminwater are particularly worrisome sources of vitamins. In addition to entirely synthetic vitamin content, the beverages tend to be packed with large amounts of refined sugar and empty carbohydrates that can be detrimental to health.

Where to buy

You can compare the various vitamin supplements on the market here at PricePlow. In addition to our reviews, ingredient lists, and videos, our comparison shopping engine and price-drop notifications can help you to save 30% to 50% off of retail prices.