Vitamin basics
Small amounts. Different jobs.
Vitamins help the body carry out essential work, from making new cells to maintaining tissues. Understanding a vitamin means asking two questions: what does it do, and how does the body handle it?
Soluble means able to dissolve.
The 13 vitamins fall into two families according to whether they dissolve in fat or water. That helps explain how the body absorbs and stores them. Each vitamin also has its own biological job.
Source: MedlinePlus vitamin guideFat-soluble vitamins
- A
- D
- E
- K
- Getting into the body
- These vitamins dissolve in fats. Dietary fat helps the intestine absorb them.
- Keeping a reserve
- The body can keep reserves in the liver and fatty tissues. The amount stored and how quickly it is used vary by vitamin.
- An exception to remember
- Vitamin K is processed relatively quickly and has smaller tissue stores than the other fat-soluble vitamins. See the source.
Water-soluble vitamins
- C
- B1 · thiamin
- B2 · riboflavin
- B3 · niacin
- B5 · pantothenic acid
- B6
- B7 · biotin
- B9 · folate
- B12
- Getting into the body
- These vitamins dissolve in water. Their absorption still depends on the vitamin and the digestive system.
- Keeping a reserve
- Reserves are generally more limited, and excess can leave through urine. Regular intake matters, but storage is not identical for every vitamin.
- An exception to remember
- Vitamin B12 is a major exception: the body can store enough to last for years. See the source.
Storage is part of the story.
The amount matters too
Water solubility does not make unlimited amounts safe. For example, excessive vitamin B6 from supplements can damage nerves. A vitamin's effects depend on the amount and form as well as its solubility.
Source: NIH vitamin B6 guideFollow the job, too
Vitamin C and vitamin B6 are both water-soluble, but they do different work. Vitamin C helps make collagen; vitamin B6 helps make chemical messengers for nerve cells. Knowing the family is a starting point for understanding each vitamin.
What happens when reserves run low?
Follow vitamins and minerals through intake, absorption, storage and loss in the next lesson.
Explore storage and depletionExplore each vitamin's work.
Start with these vitamin profiles in the Atlas. Each one explains the process, the body connection and the reference food amounts.
- Vitamin KVitamin K helps the body prepare proteins used in blood clotting and bone metabolism. These are different jobs performed by different proteins.
- Vitamin CVitamin C helps make the body's connective tissue, supports immune-cell activity and helps protect cells from damage caused by reactive molecules.
- Vitamin AVitamin A helps the eyes respond to light, supports the immune system and helps cells develop into the specialized types the body needs.
- FolateFolate, also called vitamin B9, helps cells make genetic material and divide. Its work supports the ongoing creation and replacement of cells throughout the body.
- Vitamin B6Vitamin B6 helps enzymes process nutrients and make chemical messengers that nerve cells use to communicate. It helps the body use food; it does not supply calories itself.
Sources & references (4)
- Vitamin K: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsVitamin K's role in normal blood coagulation and bone protein metabolism.Source details in the Atlas: Vitamin K: Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/
- Vitamins: Medical Encyclopedia · National Library of Medicine, MedlinePlusVitamin families, absorption and storage; vitamin B12 as a storage exception among water-soluble vitamins.Source details in the Atlas: Vitamins: Medical Encyclopediahttps://medlineplus.gov/ency/article/002399.htm
- Vitamin B12: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsWater-soluble vitamin B12 and the body's substantial stores, which can delay deficiency for years.Source details in the Atlas: Vitamin B12: Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
- Vitamin B6: Fact Sheet for Consumers · National Institutes of Health, Office of Dietary SupplementsEnzyme reactions and the risk of nerve damage from excessive supplemental vitamin B6; water solubility does not mean unlimited intake is safe.Source details in the Atlas: Vitamin B6: Fact Sheet for Consumershttps://ods.od.nih.gov/factsheets/VitaminB6-Consumer/