All About Water-Soluble Vitamins

Last Updated on: June 21, 2022

Vitamins are often categorized based on their solubility in water or fat. This blog will cover the ins and outs of water-soluble vitamins.

Human beings need micronutrients to fuel a host of bodily functions and maintain overall good health. Vitamins (along with minerals) fall into the category of micronutrients and further break down into fat soluble and water soluble.

Water-soluble vitamins are those that dissolve in water, and because the adult body is 60% water, such vitamins are easily broken down, absorbed into the bloodstream, and circulated throughout the body. Our bodies don’t generally store water-soluble vitamins; the kidneys continuously regulate their levels and send excess out of the body in urine. However, some can stay in the body for long periods. For example, you probably have several years’ supply of vitamin B12 in your liver. Folic acid and vitamin C stores can last more than a couple of days. Generally, though, water-soluble vitamins should be replenished every few days. (1, 2)

Because the body excretes excess water-soluble vitamins, taking more than the recommended daily allowance (RDA) in a supplement will not help with any given problem. For instance, taking more than the RDA of vitamin C will not help decrease the duration of a cold once you have it or ease the symptoms. Unused vitamin C will go to waste. Some nutritionists argue that unless your health care provider has advised you to take vitamins or supplements, your monthly investment would be better spent on fresh produce. (3, 4)

Which Vitamins Are Water Soluble?

There are nine water-soluble vitamins in our diets. These include eight B vitamins and vitamin C. For the recommended daily amount (RDA) of these vitamins, see the chart in “The Recommended Daily Allowance for Water-Soluble Vitamins” section in this blog.

B Vitamins (#1-8)

The eight B vitamins are collectively called B complex. All of the B vitamins serve as coenzymes in the body. Coenzymes are small compounds that help enzymes trigger chemical reactions that otherwise wouldn’t happen.

  1. Vitamin B1 or thiamine (also spelled “thiamin.” Thiamine is involved in many essential chemical reactions. For instance, it helps convert nutrients into energy and supports sugar formation. (5)
    1. Dietary sources: Liver, pork, seeds, and whole-grain cereals. About half of the thiamine in the U.S. diet comes from foods that naturally contain thiamine; the remainder comes from foods to which thiamine has been added (breads and cereals). Heating foods can reduce their thiamine content. For example, bread has 20% to 30% less thiamine than its raw ingredients, and pasteurization reduces thiamine content (which is very small to begin with) in milk by up to 20%. (6)
    2. Deficiency: Uncommon in developed countries. Diabetes, excessive alcohol intake, positive HIV/AIDS status, and taking some medications increase the risk. Serious deficiency may result in diseases such as beriberi (characterized by peripheral neuropathy and weight loss) and Wernicke-Korsakoff syndrome (characterized by peripheral neuropathy, severe short-term memory loss, and disorientation). (6)
    3. Toxicity: Excess thiamine in the body does not appear to be toxic. Scientists theorize that this is because the rate of absorption falls rapidly when the body detects a thiamine level above 5 mg. (6)
  2. Vitamin B2 or riboflavin. Vitamin B2 helps convert nutrients into energy. It is also required to convert vitamin B6 to its active form and tryptophan into niacin (vitamin B3). (5)
    1. Dietary sources: Eggs, organ meats, low fat milk, asparagus, broccoli, spinach, fortified cereals, bread, and grain products. (7)
    2. Deficiency: Very rare in developed countries. Riboflavin deficiency can cause skin disorders, sores at the corners of the mouth, swollen and cracked lips, hair loss, sore throat, liver disorders, and problems with your reproductive and nervous systems. Severe, long-term riboflavin deficiency causes anemia and cataracts. (7)
    3. Toxicity: B2 has not been shown to cause harm or interact with any medications. (7)
  3. Vitamin B3 or niacin. Vitamin B3, which is really a group of nutrients, is important for the development and function of cells and is the only B vitamin that your body can produce from another nutrient — the amino acid tryptophan. One of niacin’s most important tasks is the extraction of energy from glucose, called glycolysis. (5)
    1. Dietary sources: Yeast extract spread is exceptionally rich in niacin, providing around 25% of the RDA. Other good sources include fish, chicken, eggs, dairy products, peanuts, sunflower seeds, turkey, lamb liver, and mushrooms. Breakfast cereals and flour are often fortified with niacin. (8, 9)
    2. Deficiency: Very rare in developed countries. However, people with alcohol addiction, anorexia, inflammatory bowel disease, or liver cirrhosis, or people whose diets have too little iron, riboflavin, or vitamin B6 may develop niacin deficiency, called pellagra. Symptoms of pellagra include rough skin that turns red or brown in the sun, a bright red tongue, vomiting, constipation or diarrhea, depression, exhaustion, hallucinations, and loss of memory. (10)
    3. Toxicity: The niacin that food and beverages naturally contain is safe. However, dietary supplements with 30 mg or more can make the skin on your face, arms, and chest turn red and burn, tingle, and itch. These symptoms can also lead to headaches, rashes, and dizziness. Higher doses can cause more severe side effects. (10)
  4. Vitamin B5 or pantothenic acid. Pantothenic acid plays a key role in a wide range of metabolic functions. It is required for the formation of fatty acids, amino acids, steroid hormones, neurotransmitters, and other important compounds. (5)
    1. Dietary sources: Found in virtually all foods. Best sources include beef liver, sunflower seeds, trout, and shiitake and portobello mushrooms. (5)
    2. Deficiency: Very rare in the U.S. Severe deficiency can cause numbness and burning of the hands and feet, headache, extreme tiredness, irritability, restlessness, sleeping problems, gastrointestinal problems, and loss of appetite. (11)
    3. Toxicity: Safe even at high doses. (5, 11)
  5. Vitamin B6. A family of related compounds, vitamin B6 is crucial for more than 100 enzyme reactions involved in metabolism. Vitamin B6 is also involved in brain development during pregnancy and infancy, as well as immune function. (5, 12)
    1. Dietary sources: Pistachios, beef and lamb liver, salmon, sunflower seeds, tuna, pork, turkey, bananas, chickpeas, and potatoes. Vitamin B6 is also added to breakfast cereals and soy-based meat substitutes. (5)
    2. Deficiency: Uncommon in the U.S. but can occur more often in people with alcohol addiction, certain autoimmune disorders, and those whose kidneys do not function properly. B6 deficiency symptoms include anemia, itchy rashes, scaly skin on the lips, cracks at the corners of the mouth, a swollen tongue, depression, confusion, and a weak immune system. (5, 12)
    3. Toxicity: People almost never get too much vitamin B6 from food or beverages. However, high levels of vitamin B6 from supplements for a year or longer can cause severe nerve damage, painful skin patches, extreme sensitivity to sunlight, nausea, and heartburn. (5, 12)
  6. Vitamin B7 or biotin. Vitamin B7 is often taken for healthy hair, skin, and nails, although there is little science to support this benefit. This vitamin is crucial for fatty acid synthesis, the formation of glucose, and metabolizing amino acids. (5) (13)
    1. Dietary sources: Fish, meat, egg yolks, dairy products, legumes, leafy greens, cauliflower, mushrooms, and nuts. Your gut microbiome also produces small amounts of biotin. (5, 13)
    2. Deficiency: Very rare in the U.S. Infants who drink formula with low amounts of biotin are the most susceptible to deficiency along with people who take medications for epilepsy. Symptoms of B7 deficiency include thinning hair and loss of body hair, rashes (especially on the face), pinkeye, high levels of acid in the blood and urine, seizures, brittle nails, and nervous system disorders. (5, 13)
    3. Toxicity: No known adverse effects at high doses. May interact with some medications. (5, 13)
  7. Vitamin B9 or folate. Your body needs folate to produce DNA and cell division, especially during periods of rapid growth, such as pregnancy and infancy. (5, 14)
    1. Dietary sources: Beef and lamb liver, edamame, peanuts, raw spinach and other leafy greens, chickpeas, sunflower seeds, and asparagus. The following foods are often fortified with B9: enriched bread, flour, cornmeal, pasta, rice, breakfast cereals, and corn masa flour. (5, 14)
    2. Deficiency: Rarely occurs on its own; folate deficiency can occur when a person is deficient in other nutrients. Anemia is a classic symptom of both B9 and B12 deficiency. (5, 14)
    3. Toxicity: No side effects of high B9 intake have been reported. However, you should not consume folate in supplements or fortified foods unless your doctor recommends it because folate supplements can mask B12 deficiency. (5, 14)
  8. Vitamin B12 or cobalamin. This vitamin is responsible for maintaining neurological function, helping produce red blood cells, converting protein and fat into energy, and helping in cell division and DNA synthesis. B12 is unusual among water-soluble vitamins because it can be stored in the liver. (5, 15)
    1. Dietary sources: Fish, meat, poultry, eggs, dairy products. Clams and beef liver are some of the best sources of vitamin B12. Only animal foods contain B12; plant sources (breakfast cereals, for example) must be fortified with it. (5, 15)
    2. Deficiency: Affects adults over 50 because many don’t have enough stomach acid to absorb the B12 in food. People with pernicious anemia and those with certain gastrointestinal problems can also have trouble absorbing vitamin B12. Symptoms of B12 deficiency can take years to appear but include anemia, pale skin, heart palpitations, loss of appetite, weight loss, infertility, nerve problems, balance issues, poor memory, and soreness of the mouth or tongue. (5, 15)
    3. Toxicity: B12 has not been shown to cause harm, even in high doses. Certain medications can lower serum B12. (5, 15)
Citrus fruits are good sources of vitamin C.

Vitamin C (#9)

Also known as ascorbic acid, vitamin C is an antioxidant, meaning it fights free radicals to reduce oxidative stress. Immune cells contain vitamin C, which is depleted as they fight infections. Also, vitamin C is vital for helping the body synthesize collagen, the main protein in connective tissue and a crucial protein in wound healing. (5, 16)

  • Dietary sources: Guava (best source), citrus fruits, red and green peppers, kiwi, broccoli, strawberries, cantaloupe, potatoes, and tomatoes. Some foods and beverages may be fortified with vitamin C; check labels to see if vitamin C has been added. It’s important to be aware that heat and prolonged storage deplete the vitamin C content in food. If you can, eat fruit and vegetable sources of vitamin C raw. (5, 16)
  • Deficiency: Vitamin C deficiency is called scurvy, and it can be fatal. Symptoms of this disease include fatigue, small red or purple spots on the skin, joint pain, poor wound healing, swollen or bleeding gums, and loosening or loss of teeth. People with scurvy can also develop anemia. People who smoke, those who eat a limited variety of foods, and people with certain medical conditions, such as severe malabsorption disorders and some types of cancer, are at risk for vitamin C deficiency. (5, 16)
  • Toxicity: Vitamin C toxicity is rare, but taking more than the RDA can cause diarrhea, nausea, and stomach cramps. In people whose bodies store too much iron, high doses of vitamin C could worsen the condition and damage body tissues. Vitamin C can also interact with some medications. (5, 16)

The Recommended Daily Allowance for Water-Soluble Vitamins

The Food and Nutrition Board (FNB) at the Institute of Medicine, National Academy of Sciences has developed the RDA for many nutrients. The RDA, which is determined by age and sex, is defined as “the average daily level of intake sufficient to meet the nutrient requirements of nearly all (97% to 98%) healthy individuals.” (17)

Water-soluble vitamins are those that dissolve in water.

The Takeaway

According to the federal government’s Dietary Guidelines for Americans, for optimal health, you should get all of the nutrients you can from healthy foods and beverages. This, of course, includes water-soluble vitamins. Not only does food contain these micronutrients, but it contains dietary fiber and other beneficial components not found in supplements. In some cases, however, dietary supplements can help meet your RDA for one or more nutrients that you’re missing or not absorbing well. Always ask your doctor which supplements you may need. (18)

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