The ABCs - and Ds, Es, and Ks - of Vitamins
By Barbara Sherwood, MS, RDN
Oct 11, 2017
Updated Oct 25, 2023
5 min read
Good nutrition is an important part of a healthy lifestyle, but most of us find it hard to meet the daily recommendations from Choose My Plate. The gaps we have in eating a well-balanced daily diet make it easy to understand why the nutritional supplement industry (think vitamins and other nutritional additives, natural or synthetic) is a $41 billion business.
But are daily supplemental vitamins necessary? What are vitamins? What do they do? And how do they work in our body?
Understanding the ABCs of vitamins is important when you’re deciding between making an investment into supplementing with vitamins or investing in better quality foods.
Our bodies need 13 essential vitamins to function. Vitamins are organic compounds that come primarily from the foods we eat. They’re needed in small quantities to sustain life.
All of these essential vitamins play important roles in the body such as digestion, vision, nerve function, bone health, and support of our immune system. Vitamins are broken up into two categories: water-soluble and fat-soluble.
Water-soluble vitamins dissolve in water and aren’t stored by the body; any excess is eliminated by the kidneys. Since these vitamins don’t stay in the body, a continuous daily supply is needed in our diet. Water-soluble vitamins are made up of eight B vitamins (the B vitamin complex) and vitamin C.
The eight B vitamins that make up the “B complex” are thiamin (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), vitamin B6 (pyridoxine), folate (folic acid), vitamin B12, biotin, and pantothenic acid). B vitamins are found in a variety of animal and plant sources of foods.
Vitamin C is widely known for its function as an antioxidant that improves the immune health. However, vitamin C also plays a key part in wound healing, bone and tooth formation, strengthening blood vessel walls, and holding cells together through collagen synthesis.
Vitamin C helps with the absorption and utilization of iron. The most well-known source of vitamin C is citrus fruit, but you can also get vitamin C from potatoes, strawberries, green and red bell peppers, broccoli, brussels sprouts and kiwifruit.
Unlike their water-soluble cousins, fat-soluble vitamins are stored in the liver and fatty tissue of the body. Because surplus amounts of fat-soluble vitamins go to the liver for storage, potential health risks are associated with having too much of them in the body.
The fat-soluble vitamins are A, D, E, and K. Vitamin A is consumed primarily from animal sources of food or, if needed, the human body can convert beta-carotene found in plant sources into vitamin A — for example carrots, spinach, beets. This vitamin plays multiple roles: eye health, bone growth, tooth development, reproduction, cell division, and regulation of the immune system.
Vitamin A is also an important antioxidant. However, consuming too much Vitamin A over an extended period of time can be toxic. The body won’t convert beta-carotene into vitamin A when there are adequate amounts of the vitamin in the body. Because of this natural process, foods with beta-carotene don’t cause vitamin A toxicity.
Vitamin D, known as the sunshine vitamin, has been popular recently thanks to the vast role it plays in our health. Functionally, vitamin D aids in the absorption of calcium and phosphorus, bringing both to our bones and teeth, and regulates how much calcium remains in our blood.
Vitamin D also plays a role in muscle function and allows the brain and body to communicate through our nervous system. This vitamin has also been linked to improving symptoms of depression.
The three sources of Vitamin D are diet, sunlight, and supplementation (vitamins or fortified dairy products). The food sources of vitamin D are somewhat limited, but include milk and other fortified dairy products, cod and oily fish (herring, sardines, salmon), and mushrooms. The body has the unique ability to produce vitamin D through the skin in response to direct sunlight. Getting outside is one way to increase our daily dose of vitamin D.
Vitamin E’s primary function is an antioxidant protecting red blood cells, vitamins A and C, and essential fatty acids from destruction. Vitamin E sources include vegetable oil, fruits and vegetables, grains, nuts (almonds and hazelnuts), seeds (sunflower), and fortified cereals.
Vitamin K plays a key role in helping the blood clot, which prevents excessive bleeding. The main dietary sources of the vitamin are from leafy greens. Vitamin K is another vitamin the body has the unique ability to produce on its own. Bacteria synthesize it during digestion in the intestinal system. Because the body produces ample amounts of vitamin K, there’s little need to supplement this vitamin.
Regardless if a vitamin is water- or fat-soluble, the human body only needs small amounts. When you eat a balanced diet there’s rarely a need to supplement at all. But certain medical conditions, malabsorption disease, poor intake, pregnancy, and lack of sunlight may make it necessary to supplement with additional vitamins and minerals.
In addition to people with these and other medical conditions, these groups of people could benefit from dietary supplements:
In all cases and conditions, it’s best to check with a registered dietitian or your doctor regarding supplementing vitamins in your daily diet. Supplements can interact with medications you may be taking and cause them to be inactive or hyperactive. Vitamins can be an expensive investment and may not do much at all.
Our bodies are complex and the best way to get your essential vitamins is to eat whole, real foods that are high in nutrients and low in calories. If you’re healthy and eat a well-balanced diet, chances are good you don’t need to take additional vitamins.