8.2 Where Vitamins Come From

Janet Colson; Sarah Harris

Chapter 8 – Vitamins

8.2 Where Vitamins Come From

Vitamins in Food

Eating a variety of foods from all food groups is the best way to get the vitamins needed for good health. Different foods provide different vitamins, so including a wide range of fruits, vegetables, grains, protein foods, and dairy helps meet vitamin needs (see Figure 8.3). In general, whole foods contain more vitamins than processed foods. For example, a whole baked potato provides more vitamin C and folate than a potato cut, soaked, and fried into French fries. This type of processing and cooking can reduce vitamin content.

A chart depicts each food group of MyPlate and lists which vitamins and minerals are commonly included in that food group. Fruit: Vitamins include vitamin C, folate, vitamin A (in the form of beta-carotene). Minerals include potassium. Vegetables: Vitamins include vitamins C and K, folate, vitamin A (in the form of beta-carotene). Minerals include potassium and magnesium. Protein: Vitamins include vitamins A, D, and E and the B vitamins. Minerals include iron, zinc, and magnesium. Grains: Vitamins include B vitamins. Minerals include iron, magnesium, and selenium. Dairy: Vitamins A and D (fortified) and vitamin B12. Minerals include calcium, potassium, and phosphorous. — **Figure 8.3.** Common vitamins and minerals found in each food group. (Image by Heather Leonard licensed CC BY 4.0.)

From Plant to Plate: How Vitamins Develop and Change

Foods generally contain the highest levels of vitamins when they are allowed to fully ripen on the plant. During growth and ripening, plant enzymes actively synthesize vitamins and phytochemicals needed to support the plant’s metabolism and survival. The amount of vitamins present can vary depending on the stage of ripeness, with many vitamins increasing as fruits and vegetables mature. Vitamin content can also vary within the plant; for example, peels and outer leaves often contain higher concentrations of vitamins than the inner pulp or flesh.

Harvesting fruits and vegetables at peak ripeness helps maximize their vitamin content, and eating freshly harvested produce usually provides the greatest vitamin benefit to the body. However, not all foods can be eaten immediately after harvest. The way foods are handled, processed, stored, and prepared can impact the amount of vitamins that remain in the final product.

Food processing plays a crucial role in the food supply by enhancing safety, extending shelf life, and increasing year-round access to food. Methods such as freezing and canning can help preserve vitamins, especially when foods are processed soon after harvest. In some cases, processed foods may retain vitamins more effectively over time than fresh foods that are stored for extended periods.

Vitamin losses during processing vary by vitamin and the specific processing method. Water-soluble vitamins, such as vitamin C and many B vitamins, are the most sensitive to heat, light, water, and oxygen, making them more susceptible to degradation during processing and cooking.

**Table 8.1: The effects of processing on nutrient retention** ^[1]
Method of Processing	Effect on Nutrient Retention	How to Minimize Nutrient Loss
Air exposure and time	Enzymes present in foods and exposure to air can destroy nutrients. As soon as the food is harvested, it begins to slowly decompose.	Purchase fresh items in quantities that can be used as soon as possible. Cut up foods only when ready to use. Buy local produce to reduce transport time and exposure to air.
Temperature	Cooking helps kill bacteria, makes foods more appealing, and in some situations improves the bioavailability of nutrients. However, prolonged exposure to high temperatures can destroy certain vitamins.	Use fast-cooking methods such as microwaving, steaming, or stir-frying.
Water	Minerals and water-soluble vitamins can leach into the water.	Don’t soak produce in water. Limit the amount of water used to cook foods (e.g., steam vegetables rather than boil them). Use cooking water in food preparation.
Canning	High temperatures can be used, which can destroy water-soluble vitamins, but commercial techniques usually use rapid heating to help reduce nutrient loss.	Choose a variety of canned goods that don’t have added sugars or sodium to maximize nutrient density.
Freezing	Freezing does not reduce nutrient content, but if foods are blanched prior to freezing, it may slightly reduce levels of water-soluble vitamins.	Choose a variety of frozen goods that don’t have added sugars, syrups, or sauces to maximize nutrient density.
Refining of grains	Many B vitamins, minerals, and phytochemicals, as well as fiber, are lost when whole grains are refined.	Choose whole grains whenever possible.

There is an important exception to the usual effects of processing on vitamins. Unlike most vitamins, the bioavailability of beta-carotene—a precursor to vitamin A— and other carotenoids actually increases with cooking. Chopping, cooking, and blending help break down the plant’s cell structure, releasing carotenoids and making them more easily absorbed by the body. As a result, cooked carrots can provide more usable vitamin A than raw carrots.

However, excessive heat can damage carotenoids and convert some into inactive forms. To maximize vitamin A availability, vegetables rich in carotenoids are best chopped and lightly cooked, such as by steaming, rather than overcooked.

When the Body Makes Its Own Vitamins

Although most vitamins must come from the foods we eat, the body can produce limited amounts of certain vitamins on its own. In some cases, the body uses substances it naturally makes to produce vitamins. In other cases, vitamins are formed from precursor compounds found in foods. Beneficial bacteria in the intestinal tract can also produce small amounts of certain vitamins.

Vitamin D is unique because the body can make it from cholesterol, a substance naturally produced in the liver and found in body tissues. When ultraviolet (UV) rays from sunlight reach the skin, they trigger a series of reactions that convert a form of cholesterol into vitamin D. The amount produced depends on factors such as season, geographic location, skin exposure, skin pigmentation, and time spent outdoors. When sunlight exposure is limited, foods such as fatty fish and fortified milk become important sources of vitamin D.

In contrast, vitamin A and niacin are produced from dietary precursors.

Vitamin A can be formed from beta-carotene, a red-orange pigment found in plant foods such as carrots, sweet potatoes, and pumpkins. The body converts beta-carotene into active vitamin A, mainly in the small intestine. Animal foods such as milk, eggs, and liver also provide preformed vitamin A, called retinol.
Niacin can be synthesized in the liver from tryptophan, an amino acid found in protein-rich foods such as turkey, chicken, eggs, dairy products, and fish. However, this conversion depends on adequate intake of protein and several other nutrients involved in the process.

These examples illustrate that although the body can produce some vitamins under certain conditions, most still need to come from a balanced, varied diet.

Vitamins and Pigments in Carrots

Carrots were not always orange. The earliest carrots, first cultivated more than 1,000 years ago, were usually purple or yellow. Orange carrots were later developed because they contain high amounts of beta-carotene, a plant pigment that the body converts into vitamin A.^[2] Vitamin A is important for healthy vision, immune function, and normal growth.

Purple carrots contain different plant compounds called anthocyanins, which give them their deep purple color. Anthocyanins act as antioxidants, helping protect cells from damage. These pigments are also more stable during cooking and food processing, which is why purple carrots are sometimes used as natural food colorings.

The different colors of carrots reflect the presence of different beneficial plant compounds, often called phytochemicals s. Eating a variety of colorful vegetables, including different types of carrots, can provide a wider range of nutrients and health-promoting compounds.

ARS researchers have selectively bred carrots with pigments that reflect almost all colors of the rainbow. More importantly, though, they're very good for your health." — USDA ARS — [pb_glossary id="3246"]anthocyanin[/pb_glossary] **Figure 8.4.** A rainbow of carrots. (“Carrots of many colors cutout” by USDA, Public Domain.)

Vitamins Made by Bacteria within the Human Intestines

Some vitamins can be synthesized not by our bodies, but by the helpful bacteria living within us. Bacteria in the gut can make vitamin K and the B vitamins.

Bacteria that colonize the large intestine can synthesize one form of vitamin K, although the total amount made in the large intestine is not clear. ^[3]

Natto: An excellent source of Vitamin K

Natto is easy to recognize by its sticky, stringy texture and glossy soybeans—features that come from fermentation with Bacillus subtilis. — **Figure 8.5.** “Natto mixed” by Kinchan1 licensed CC BY 2.0.

Natto is easy to recognize by its sticky, stringy texture and glossy soybeans—features created during fermentation. This process, carried out by the bacterium Bacillus subtilis, not only gives natto its distinctive texture but also produces large amounts of vitamin K₂ (menaquinone). As a result, natto is one of the richest dietary sources of this important vitamin.

Gut bacteria are also able to make the B vitamins, though the amount synthesized of each vitamin is dependent on the composition of each individual’s microbiome.^[4] Dietary choices (e.g., intake of high fiber foods or probiotics) and medication use can alter a person’s microbiome, possibly promoting or inhibiting the production of vitamins in the large intestine.

Review Questions

attributions

This section is an adaptation of “Sources of Vitamins and Minerals” in Nutrition: Science and Everyday Application, v. 1.0 by Alice Callahan, PhD; Heather Leonard, MEd, RDN; and Tamberly Powell, MS, RDN, licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Devi R. Food processing and impact on nutrition. Research Scholar, Department of Economics, Kurukshetra University, Kurukshetra, Haryana, India. Published 2005. Accessed January 4, 2025. http://saspjournals.com/wp-content/uploads/2015/08/SJAVS-24A304-311.pdf ↵
Maron DF. How orange carrots conquered the world. Nature. 2023;622:221. doi:10.1038/d41586-023-03035-0. ↵
Gu Q, Li P. Biosynthesis of vitamins by probiotic bacteria. In: Probiotics and Prebiotics in Human Nutrition and Health. IntechOpen; 2016. Accessed January 4, 2026. https://www.intechopen.com/books/probiotics-and-prebiotics-in-human-nutrition-and-health/biosynthesis-of-vitamins-by-probiotic-bacteria ↵
Yoshii K, Hosomi K, Sawane K, Kunisawa J. Metabolism of dietary and microbial vitamin B family in the regulation of host immunity. Front Nutr. 2019;6:48. doi:10.3389/fnut.2019.00048 ↵

License

Icon for the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

Introduction to Nutrition and Wellness, 2nd Edition Copyright © 2026 by Janet Colson and Sarah Harris is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.