Vitamin C: Ascorbic Acid

Vitamin C, also known as ascorbic acid, is a water-soluble vitamin that must be obtained from the diet because the body cannot produce it.

Functions of Vitamin C

Like vitamin E (discussed in the previous section), vitamin C acts as an antioxidant, helping protect cells from damage caused by free radicals. It also helps regenerate vitamin E, allowing it to continue its protective role.

Vitamin C also plays an important role in iron absorption. It enhances the absorption of nonheme iron (the form found in plant foods) by converting it to a form that is easier for the body to absorb. This is why pairing foods like beans or spinach with vitamin C–rich foods can improve iron status.

One of vitamin C’s most important functions is in the production of collagen, the protein that provides strength and structure to the skin, blood vessels, gums, and other connective tissues. Figure 8.17 illustrates vitamin C’s role in collagen formation.

When vitamin C intake is too low, the body cannot produce strong, stable collagen. As a result, collagen fibers become weak, leading to fragile tissues and impaired wound healing. Because collagen is essential for maintaining tissue integrity, inadequate vitamin C can slow healing and contribute to symptoms such as bleeding gums and poor recovery from injuries.

---

Vitamin C is not stored in large amounts in the body. The body absorbs what it needs, and the kidneys excrete any excess. Because of this, vitamin C must be consumed regularly through the diet.

Scurvy (Vitamin C Deficiency)

Scurvy is a disease caused by a lack of vitamin C. Because vitamin C is essential for collagen production, deficiency weakens connective tissues throughout the body. One of the most noticeable signs is bleeding gums, which occur when fragile blood vessels and gum tissue break down. Other symptoms include poor wound healing, joint pain, fatigue, and increased risk of infections.

Although rare today, scurvy can still develop in individuals with very limited diets lacking fruits and vegetables. ^[1]

Vitamin C and Chronic Disease

Vitamin C has been studied for its role in preventing chronic diseases. Research suggests that the greatest health benefits come from eating vitamin C-rich foods, such as fruits and vegetables, rather than taking supplements.

Heart Disease and Stroke: People who eat more fruits and vegetables tend to have a lower risk of heart disease and stroke. Higher blood levels of vitamin C are associated with better heart health, but these benefits appear to come from a healthy diet—not vitamin C supplements.

Cancer: Diets rich in fruits and vegetables are associated with a lower risk of some cancers. Researchers believe this is due to the many beneficial compounds in these foods, not vitamin C alone.

Immune Function and Colds: Vitamin C supports normal immune function, but it does not prevent the common cold for most people. Regular vitamin C intake may slightly shorten a cold, but large supplement doses provide little additional benefit.

Gout: Some studies suggest that people who consume more vitamin C may have a lower risk of gout, but more research is needed.

Key Point: The strongest evidence supports getting vitamin C from whole foods, especially fruits and vegetables, rather than from supplements. Whole foods provide vitamin C along with fiber and many other beneficial compounds that work together to promote health.^[2]

How Much Vitamin C Do We Need?

The Recommended Dietary Allowance (RDA) for vitamin C varies by age and sex. Young children ages 1–3 need 15 mg per day, while adult women need 75 mg per day and adult men need 90 mg per day. These recommended amounts are designed to prevent scurvy and to support normal immune function and overall health.

Because smoking increases free radicals in the body, smokers need an extra 35 milligrams of vitamin C per day compared to non-smokers. Although quitting smoking is the best recommendation, choosing vitamin C–rich foods—such as oranges, strawberries, bell peppers, broccoli, and tomatoes—can help those who continue to smoke meet this higher need naturally.

What are the best Sources of Vitamin C?

Citrus fruits are excellent sources of vitamin C, and so are many vegetables. In fact, British sailors in the past were often referred to as “limeys” as they carried sacks of limes onto ships to prevent scurvy. Vitamin C is not found in significant amounts in animal-based foods.

Because vitamin C is water-soluble, it leaches away from foods considerably during cooking, freezing, thawing, and canning. Up to 50 percent of vitamin C can be boiled away. Therefore, to maximize vitamin C intake from foods, you should eat fruits and vegetables raw or lightly steamed. For the vitamin C content of various foods, see Figure 8.19.

B-Complex Vitamins

The B-complex vitamins are a group of eight water-soluble vitamins that help the body convert food into energy, support the nervous system, and promote the formation of healthy red blood cells. Although grouped together, each B vitamin has a unique role in maintaining health.

The discovery of the B vitamins began in the late 1800s, when scientists searched for the cause of beriberi, a disease that causes weakness, nerve damage, and heart problems. Beriberi was common among people who ate polished white rice but rare in those who consumed whole rice. Researchers eventually discovered that removing the outer layers of the rice also removed an essential nutrient—thiamin (vitamin B₁).

In 1912, Polish biochemist Casimir Funk isolated a substance from rice bran that helped prevent beriberi. He proposed that certain diseases were caused by deficiencies in essential nutrients and introduced the term "vitamine," which was later shortened to "vitamin." His work helped establish the concept that specific nutrients are required in the diet to prevent deficiency diseases.

Today, the B-complex vitamins are recognized as a family of eight water-soluble vitamins that help the body produce energy, support brain and nerve function, synthesize DNA, and form healthy red blood cells. Although scientists once thought vitamin B was a single nutrient, they later discovered it was actually a group of eight related vitamins that often occur together in foods and work together in metabolism. Because they are not stored in large amounts in the body, they must be consumed regularly through a balanced diet.

The B-complex vitamins are often grouped by their primary functions. Thiamin, riboflavin, niacin, pantothenic acid, and biotin primarily help the body release energy from food. Vitamin B₆ plays a major role in protein metabolism, while folate and vitamin B₁₂ are especially important for DNA synthesis and the formation of healthy red blood cells.

Thiamin (B₁).  Riboflavin (B₂), Niacin (B₃)

Thiamin (vitamin B₁) plays a key role in energy metabolism, especially in the breakdown of carbohydrates, and is essential for normal nerve and muscle function. One of the richest natural sources of thiamin is pork, which contains levels much higher than those in most other meats. Highly fortified breakfast cereals, such as Total®, are also excellent sources of thiamin and provide a reliable way to meet daily needs.  Even cereals packed with added sugars typically contain 20% of the Daily Value for most B vitamins.

Riboflavin (vitamin B₂) is involved in energy production and helps maintain healthy skin and eyes. Riboflavin has a distinctive bright yellow-green (fluorescent) color when exposed to ultraviolet light. Because riboflavin is destroyed by light, foods that contain it—especially milk—are packaged in opaque containers to protect the vitamin from degradation. Fortified breakfast cereals and pork also contribute to the diet's riboflavin intake.

Niacin (Vitamin B₃) plays a key role in energy metabolism, DNA repair, and nervous system function.  Niacin also supports healthy skin and proper digestion.  In addition to dietary sources such as pork, poultry, fish, peanuts, and fortified cereals, the body can synthesize niacin from the amino acid tryptophan, provided overall protein intake is adequate.

Niacin deficiency leads to pellagra, a condition classically described by the “four Ds”: dermatitis, diarrhea, dementia, and, if untreated, death. The dermatitis associated with pellagra is characterized by rough, darkened, scaly skin that typically appears on sun-exposed areas. Pellagra was historically common in populations whose diets relied heavily on corn-based staples lacking adequate niacin or tryptophan.

Pantothenic Acid (B₅), and Biotin (B₇)

Biotin (vitamin B7) plays a crucial role in fatty acid synthesis and  amino acid metabolism. Eggs are an excellent source of biotin; however, raw egg whites contain a protein called avidin, which binds biotin and reduces its absorption. For this reason, eggs should be fully cooked, as heat inactivates avidin, allowing biotin to be absorbed normally. Biotin is commonly included in cosmetics and hair products, although scientific evidence supporting its effects on hair and nails in non-deficient individuals is limited.

Pantothenic acid (vitamin B₅) is required for the formation of coenzyme A (CoA), which is essential for energy metabolism and the synthesis of fatty acids and  cholesterol. Pantothenic acid is widely distributed in foods, making deficiency rare. Like biotin, pantothenic acid is frequently added to cosmetics and hair-care products, reflecting its role in skin and cellular metabolism. A deficiency in chickens results in crusty lesions, as noted in Figure 8.23.

Vitamin B₆: From PMS to Pregnancy

Vitamin B₆ (pyridoxine) is a water-soluble vitamin involved in amino acid metabolism and red blood cell formation. It also helps convert tryptophan into niacin and serotonin.

Vitamin B₆ has been studied for its potential to reduce symptoms of premenstrual syndrome (PMS), although evidence is mixed. It is also commonly used to treat nausea and vomiting during pregnancy and is often combined with doxylamine as a first-line treatment for morning sickness.

While vitamin B₆ is essential for health, high-dose supplements can cause nerve damage, leading to numbness and tingling in the hands and feet.National Institutes of Health, Office of Dietary Supplements. Vitamin B6: Fact sheet for health professionals. Updated March 26, 2025. Accessed April 26, 2026. https://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional/[/footnote]

Good food sources include poultry, fish, pork, potatoes, bananas, chickpeas, and fortified cereals.

Folate (B9): Small Vitamin, Big Role in Growth

Folate (vitamin B₉) functions as a coenzyme in DNA and RNA synthesis. Because folate is essential for cell division, tissues with rapidly dividing cells—such as the bone marrow—are most affected by deficiency. When folate intake is inadequate, cells grow but cannot divide properly, leading to macrocytic (megaloblastic) anemia, a condition characterized by fewer but abnormally large red blood cells (Figure 8.23).

Folate is especially critical during early pregnancy for the normal development of the central nervous system. Maternal folate deficiency increases the risk of neural-tube defects, including spina bifida, which occurs when the spinal cord does not fully close and can result in lifelong physical and neurological complications (Figure 8.25). Rates of neural-tube defects declined significantly in the United States and Canada after the mandatory fortification of enriched grain products with folic acid in the late 1990s. Clinical trials also show that taking folate supplements before conception and during pregnancy greatly reduces this risk, leading to a higher RDA for pregnant women.

Dietary Sources of Folate

Good sources of folate include dark leafy green vegetables, legumes, fruits, and some animal products. In the United States, the Food and Drug Administration requires certain grain products—such as breads, cereals, flours, and cornmeal—to be fortified with folic acid to help increase folate intake in the population. Figure 8.26 shows examples of foods that naturally contain folate as well as fortified foods that provide folic acid.

Dietary Reference Intakes of Folate

Vitamin B₁₂ (Cobalamin): Only in Animal Products

Vitamin B₁₂ (cobalamin) is unique because it is the only vitamin that contains the mineral cobalt. It works closely with folate to support DNA synthesis, red blood cell formation, and normal nerve function. A deficiency of either vitamin can cause macrocytic (megaloblastic) anemia, and low vitamin B₁₂ during pregnancy may also increase the risk of neural tube defects in the developing fetus.

Unlike most vitamins, vitamin B₁₂ requires a special protein called intrinsic factor, produced in the stomach, for absorption in the small intestine. Conditions that reduce intrinsic factor or damage the stomach—such as pernicious anemia, chronic stomach inflammation, or Helicobacter pylori infection—can lead to vitamin B₁₂ deficiency. Older adults are also at greater risk because vitamin B₁₂ absorption often decreases with age. Depending on the cause, treatment may include high-dose supplements or injections.

.Dietary Sources of B₁₂

Vitamin B₁₂ is found naturally in animal-derived foods, including meat, fish, poultry, eggs, and dairy products. While plant foods do not naturally contain vitamin B₁₂, fortified breakfast cereals are an important source, especially for individuals who consume little or no animal products. For the vitamin B₁₂ content of foods, see Figure 8.27. 

RELATIONSHIP BETWEEN Vitamin B_12, Folate, and Vitamin B₆

Vitamins B₆, folate, and B₁₂ work together to convert homocysteine into methionine, an amino acid needed for normal cell function. When intake of any of these vitamins is too low, homocysteine levels can increase.

High homocysteine levels have been linked to a greater risk of heart disease and stroke, although studies have not consistently shown that taking B-vitamin supplements lowers this risk. Maintaining adequate intake of these vitamins through a balanced diet supports normal homocysteine metabolism and overall health.

CHOLINE

Choline is a water-soluble compound that is not classified as a vitamin because the body can synthesize small amounts. However, this synthesis is insufficient to meet the body's needs, making choline an essential nutrient that must also be obtained from food.

Choline is required for:

• Production of the neurotransmitter acetylcholine
• Formation of cell membranes
• Lipid transport
• Homocysteine metabolism

Good dietary sources include egg yolks, meats, fish, and legumes. Choline is especially important during pregnancy because it supports normal fetal brain development. In adults, deficiency may contribute to fatty liver and muscle damage.

Most adults need 425–550 mg of choline per day. Table 8.3 lists common dietary sources of choline.

Each water-soluble vitamin has a unique job, but together they help convert food into energy, support healthy cells, and keep your body functioning properly. Use Table 8.6 as a quick review of their major functions, food sources, and deficiency conditions.

attributions

This section is an adaptation of "Water-Soluble Vitamins" in Human Nutrition: 2020 Edition by University of Hawai‘i at Mānoa Food Science and Human Nutrition Program licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.