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Storage & depletion

How the body keeps and uses its reserves.

The nutrients in a meal become part of a bigger story: what the body absorbs, what it uses, what it stores and what it loses. This lesson follows vitamins and minerals through that story.

One vitamin at a time

Where it is held. How its supply changes.

Select a vitamin to explore its body stores or working tissue pool. Compare an ongoing supply, a shortfall and replenishment. Water soluble and fat soluble describe vitamin families, not a shared storage capacity or depletion clock.

Fat-soluble vitamins
Water-soluble vitamins

Showing Vitamin A, fat-soluble. Supply meets need: the body's pool can be maintained.

Fat-soluble · storage & depletion

Vitamin A

Helps the eyes detect light and supports the protective tissues and cells involved in immune function.

Explore how Vitamin A supports the body
Where it is held

Mainly the liver

  • Liver

Most vitamin A is stored in the liver. This reserve is separate from the vitamin already working in tissues.

Schematic locations. Markers show where a vitamin is held, not the amount or how freely it can be released.

Explore a change in supply

Direction of change · conceptual

The body's pool

Can be maintained

When absorbed supply replaces ongoing use and losses, the body's pool can be maintained.

The arrow shows direction only. It does not show a measured amount, rate or time.

What affects A's supply?

A sustained shortage of absorbed vitamin A can draw down liver reserves. Starting stores and the body's ability to absorb and use vitamin A affect the course.

Why there is no fixed countdown here

The sources linked here do not establish one depletion time that applies to everyone. A measured starting reserve and defined intake would be needed for a numerical estimate.

A liver reserve can buffer a shortfall, but its size is not the same for everyone.

Sources & references (1)
  1. Vitamin A and Carotenoids: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentVitamin A's role in vision, immune function and cellular differentiation; provitamin-A vs non-provitamin-A carotenoids.Source details in the Atlas: Vitamin A and Carotenoids: Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/

Different nutrients, different reserves.

There is no single storage tank for all nutrients. These examples show why the amount stored, its location and its availability matter.

Vitamins A, D, E and K

Liver and fatty tissues

Fat-soluble vitamins can be held in reserve. Storage varies within the group: vitamin K has relatively small tissue stores.

Vitamin B12

A substantial reserve, especially in the liver

B12 is water-soluble, yet its stores can last for years. Difficulty absorbing it can still lead to deficiency even when food intake looks adequate.

Iron

Storage proteins in the liver, spleen and bone marrow

Some iron is held by proteins such as ferritin. These reserves are distinct from the iron already doing a job in hemoglobin, the blood's oxygen-carrying protein.

Calcium

Mostly bones and teeth

Bone is both structure and a calcium reserve. The body can draw on this reserve to support essential functions elsewhere, including muscle contraction and nerve communication.

Compare water-soluble and fat-soluble vitamins

Depletion means reserves are running down.

When the amount absorbed does not keep up with requirements and losses, the body may draw on its reserves. A continuing shortfall can reduce those reserves and eventually interfere with normal function. The pace differs by nutrient and by person.

01

Less coming in

Over time, intake may fall short of what the body needs. For example, prolonged low magnesium intake can lead to deficiency, even though the kidneys initially help conserve it.

02

Less being absorbed

Eating a nutrient and absorbing it are separate steps. Vitamin B12 is an example: some digestive conditions interfere with absorption even when intake is sufficient.

03

Needs increasing

Requirements can change with life stage. During pregnancy, for example, iron needs rise as blood volume expands and the developing baby needs iron.

04

More being lost

Blood loss removes iron. Diarrhea can remove fluids and electrolytes. Different losses affect different nutrients, so the cause matters.

Iron connects storage to a job in the body.

Some iron is held in storage proteins; much of the body's iron is already at work carrying oxygen. When intake and absorption cannot replace losses and meet requirements, reserves can decline. This is why the amount stored and the job a nutrient performs are separate parts of the story.

Follow iron's role in oxygen transport

Connect it to daily life.

Activity and illness change the context

Physical activity makes adequate food and fluids important. Illness can also change the picture: diarrhea, for example, causes fluid and electrolyte losses. Ask which need or loss has changed, rather than assuming every nutrient is depleted together.

Feeling depleted is a clue, not a measurement

Lack of sleep, emotional stress, activity and medical conditions can all cause fatigue. Tiredness alone cannot tell you which nutrient is low. Persistent, unexplained symptoms need an assessment of the cause.

Replenishment starts with understanding the gap.

Regular, varied food supplies nutrients over time. When absorption or ongoing losses are the problem, addressing the cause matters too. Taking more is not always better: even water-soluble vitamin B6 can cause harm in excessive supplemental amounts.

Sources & references (25)
  1. Vitamin K: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentVitamin 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/
  2. Vitamin C: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentVitamin C's role in collagen synthesis, physiological antioxidant activity and immune function.Source details in the Atlas: Vitamin C: Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
  3. Vitamin A and Carotenoids: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentVitamin A's role in vision, immune function and cellular differentiation; provitamin-A vs non-provitamin-A carotenoids.Source details in the Atlas: Vitamin A and Carotenoids: Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/
  4. Folate: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentFolate's role in DNA/RNA synthesis, amino-acid metabolism and cell division; Dietary Folate Equivalents.Source details in the Atlas: Folate: Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/Folate-HealthProfessional/
  5. Calcium: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentCalcium's role in bone structure, muscle function and nerve transmission.Source details in the Atlas: Calcium: Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/
  6. Vitamin B6: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentVitamin B6's role in metabolic and neurological functions.Source details in the Atlas: Vitamin B6: Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional/
  7. Iron: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentIron's role in hemoglobin and myoglobin oxygen transport.Source details in the Atlas: Iron: Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/Iron-HealthProfessional/
  8. Vitamin B1 (Thiamin): Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentSmall liver stores, rapid turnover, ongoing dietary supply and energy metabolism.Source details in the Atlas: Vitamin B1 (Thiamin): Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/Thiamin-HealthProfessional/
  9. Vitamin B2 (Riboflavin): Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentSmall stores in liver, heart and kidneys; metabolic roles and deficiency.Source details in the Atlas: Vitamin B2 (Riboflavin): Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/Riboflavin-HealthProfessional/
  10. Vitamin B3 (Niacin): Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentNAD and NADP tissue pools, metabolic roles and conversion from tryptophan.Source details in the Atlas: Vitamin B3 (Niacin): Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/Niacin-HealthProfessional/
  11. Vitamin B5 (Pantothenic Acid): Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentCoenzyme A in tissues; metabolic roles and the rarity of isolated deficiency.Source details in the Atlas: Vitamin B5 (Pantothenic Acid): Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/PantothenicAcid-HealthProfessional/
  12. Vitamin B7 (Biotin): Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentLiver storage, enzyme roles, recycling and factors affecting availability.Source details in the Atlas: Vitamin B7 (Biotin): Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/Biotin-HealthProfessional/
  13. Vitamin D: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentCalcium absorption, dietary supply, production in skin and factors affecting availability.Source details in the Atlas: Vitamin D: Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
  14. Vitamin E: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentAntioxidant and immune roles; fat malabsorption as a risk for deficiency.Source details in the Atlas: Vitamin E: Fact Sheet for Health Professionalshttps://ods.od.nih.gov/factsheets/VitaminE-HealthProfessional/
  15. Vitamin D: Medical Encyclopedia · National Library of Medicine, MedlinePlusGovernmentVitamin D is fat-soluble and can be stored in fatty tissue and the liver.Source details in the Atlas: Vitamin D: Medical Encyclopediahttps://medlineplus.gov/ency/article/002405.htm
  16. Vitamin E: Medical Encyclopedia · National Library of Medicine, MedlinePlusGovernmentVitamin E storage in fatty tissue and the liver; physiological roles.Source details in the Atlas: Vitamin E: Medical Encyclopediahttps://medlineplus.gov/ency/article/002406.htm
  17. Vitamin B6: Dietary Reference Intakes · Institute of Medicine, National Academies Press · 1998InstitutionalMuch of the body's PLP is found in muscle bound to phosphorylase. Tissue pools should not be treated as freely available spare reserves.Source details in the Atlas: Vitamin B6: Dietary Reference IntakesVitamin B6 chapter: absorption, metabolism and body pools. No depletion rate is derived from the pool size.https://www.ncbi.nlm.nih.gov/books/NBK114313/
  18. Severe experimental folate deficiency in a human subject · SpringerPlus · 2014Peer reviewedA single-subject depletion experiment differed markedly from earlier observations. Used to explain uncertainty, not establish a general depletion time.Source details in the Atlas: Severe experimental folate deficiency in a human subjectGolding PH. SpringerPlus 2014;3:442. doi:10.1186/2193-1801-3-442. Single-subject self-experiment; not generalizable.https://pubmed.ncbi.nlm.nih.gov/25332850/
  19. Magnesium: Fact Sheet for Consumers · National Institutes of Health, Office of Dietary SupplementsGovernmentKidney conservation of magnesium when intake is low; prolonged low intake and deficiency; food sources.Source details in the Atlas: Magnesium: Fact Sheet for Consumershttps://ods.od.nih.gov/factsheets/Magnesium-Consumer/
  20. Fatigue · National Library of Medicine, MedlinePlusGovernmentFatigue has multiple possible causes, including activity, stress and insufficient sleep; symptoms alone do not identify a nutrient deficiency.Source details in the Atlas: Fatiguehttps://medlineplus.gov/fatigue.html
  21. Treatment of Diarrhea · National Institute of Diabetes and Digestive and Kidney DiseasesGovernmentDiarrhea can cause loss of fluid and electrolytes. The Atlas uses this as an example of nutrient loss, not as a treatment guide.Source details in the Atlas: Treatment of Diarrheahttps://www.niddk.nih.gov/health-information/digestive-diseases/diarrhea/treatment
  22. Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Consumers · National Institutes of Health, Office of Dietary SupplementsGovernmentPhysical activity requires adequate food and fluids; nutrient needs and supplement effects should not be inferred from tiredness alone.Source details in the Atlas: Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Consumershttps://ods.od.nih.gov/factsheets/ExerciseAndAthleticPerformance-Consumer/
  23. Vitamins: Medical Encyclopedia · National Library of Medicine, MedlinePlusGovernmentVitamin 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
  24. Vitamin B12: Fact Sheet for Health Professionals · National Institutes of Health, Office of Dietary SupplementsGovernmentWater-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/
  25. Vitamin B6: Fact Sheet for Consumers · National Institutes of Health, Office of Dietary SupplementsGovernmentEnzyme 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/

The nutrition and biological information on this site is provided for educational purposes and is not a substitute for individualized medical advice.