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Nutrition and daily life

Vitamins: small amounts, a big role

The body needs vitamins in very small amounts, yet without them blood cells are not made, wounds do not heal and the immune system cannot work. During treatment many people think about vitamin supplements. This topic explains what vitamins do, which foods contain them and why supplements call for caution.

Last updated: ~4 min read
On a dark navy background, a cooked carrot, a red bell pepper, a bowl of cooked spinach, halved orange and kiwi, a halved hard-boiled egg, cooked salmon and a glass of milk.
Figure 1.A varied diet is the main source of vitamins.

01Short answer

Vitamins fall into two groups: fat-soluble (A, D, E, K) and water-soluble (the B group and C). In leukemia, some matter especially: folate and B12 (making blood cells), vitamin K (blood clotting), vitamin D (bones and muscles) and vitamin C (tissue repair). During treatment, the safest way is to get most vitamins from a varied, well-cooked diet. High-dose supplements, especially antioxidants, can interact with some medicines. Deficiencies are found with blood tests, and supplements are prescribed by your doctor.

02Simple explanation

Vitamins are substances the body cannot make in sufficient amounts and must get from food. They work as “helpers” for enzymes.

Fat-soluble vitamins (A, D, E, K) are stored in the liver and fatty tissue, so too much of them can be harmful.

Water-soluble vitamins (the B group and C) are hardly stored, and the excess leaves in the urine. They need to come from food regularly.

Folate and vitamin B12 are needed to make new blood cells in the bone marrow. A lack of either can cause anaemia.

Some medicines “clash” with vitamins. For example, methotrexate blocks the folate pathway, and warfarin works against vitamin K. That is why supplements are agreed with your doctor.

03Scientific explanation

Food first: the 2022 ESPEN micronutrient guideline and the ACS note that most patients can get vitamins from a varied diet; supplements are advised mainly for a confirmed deficiency or reduced food intake.

Antioxidants and chemotherapy: in the SWOG S0221 study (breast cancer, 2020), people who took antioxidant supplements (vitamins A, C, E, carotenoids, coenzyme Q10) before and during chemotherapy had a somewhat higher risk of recurrence. This is not direct evidence for leukemia, but it is a reason for caution.

Folate and B12: according to NIH ODS, both are essential for making DNA and red blood cells. Methotrexate blocks folate metabolism, so folic acid is taken only as directed by your doctor.

Vitamins K and D: according to the NHS, vitamin K is needed for blood clotting; people taking warfarin should avoid sudden changes in how much vitamin K-rich food they eat. According to NIH ODS, vitamin D deficiency is common and can be checked with a blood test.

04What happens in the body?

What do vitamins do?

They help release energy, build DNA, make blood cells, heal wounds and support eyesight and bones. Each vitamin has its own job; one cannot replace another.

Two groups

A, D, E and K are absorbed with fat and stored. The B group and C dissolve in water, are stored only a little and must come from food every day. Long boiling reduces some water-soluble vitamins.

On a dark navy background, two translucent vessels: four glowing spheres in golden oil in one, many small bright spheres dissolving in clear water in the other.
Figure 2.Some vitamins dissolve in fat, others in water.

Vitamins for the blood

Folate (green vegetables, legumes), B12 (meat, fish, eggs, milk) and B6 take part in making blood cells. In leukemia, the main cause of anaemia is usually the disease and its treatment; vitamin deficiencies are checked separately.

On a dark navy background, young red blood cells maturing in a translucent marrow cavity, with small green and ruby sparks flowing into them.
Figure 3.Folate and B12 help the bone marrow make new blood cells.

Vitamin K and clotting

Green leafy vegetables are rich in vitamin K, which helps blood clot. If you take warfarin, the point is not to ban these foods but to keep the amount you eat steady.

Vitamin D

Sunlight makes vitamin D in the skin; in food it is found in oily fish, egg yolk and fortified products. During treatment people spend a lot of time indoors, which can make deficiency worse. Your doctor checks the level with a blood test.

Care with supplements

Multivitamins, high-dose vitamins C and E and “immune” complexes can interact with medicines, strain the liver or affect bleeding. Tell your team about everything you take.

05Vitamins: four steps

Food first, remember clotting, check vitamin D, ask about supplements.

Food first — Varied and well cooked.1Food firstVaried and well cooked.
Vitamin K — Clotting and warfarin.2Vitamin KClotting and warfarin.
Vitamin D — Sun, fish, blood test.3Vitamin DSun, fish, blood test.
Ask about supplements — Only with your doctor’s agreement.4Ask about supplementsOnly with your doctor’s agreement.
Support for blood cellsEnough folate and B12.
Safe treatmentNo clashes with medicines.
Strong bonesVitamin D is monitored.

06Key vitamins (simplified)

VitaminWhat it is forFood sources
AEyesight, mucous membranesCarrots, pumpkin, egg yolk, milk
DBones, musclesOily fish, eggs, sunlight
EProtecting cell membranesVegetable oils, nuts, seeds
KBlood clottingSpinach, cabbage, broccoli, parsley
B12 and folateBlood cells, DNAMeat, fish, eggs; green vegetables, legumes
CTissue repair, iron absorptionBell peppers, citrus, kiwi, potatoes

* The table is general information. Vitamin supplements, especially during treatment, are prescribed only by your doctor.

07Key terms

Vitamin
An essential substance that must come from food.
Fat-soluble
Vitamins absorbed with fat and stored in the body.
Water-soluble
Vitamins stored only a little and needed daily.
Antioxidant
A substance that reduces oxidative damage.
Folate
A B vitamin needed for DNA and blood cells.
Methotrexate
A medicine that blocks folate metabolism.
Anticoagulant
A medicine that reduces blood clotting.
Deficiency
Having less of a vitamin than the body needs.

08Key points

  • Most vitamins can come from food.
  • Excess fat-soluble vitamins build up.
  • Folate and B12 are important for the blood.
  • On warfarin, keep vitamin K foods steady.
  • Vitamin D can be checked with a blood test.
  • Antioxidant supplements only with agreement.
  • On methotrexate, do not take folic acid on your own.
  • Tell your team about every supplement.

09Frequently asked questions

Can I take a multivitamin?

Sometimes doctors recommend a standard-dose multivitamin, especially if you are eating little. But during treatment, agree any supplement with your team first.

Will vitamin C boost my immunity?

The immune system needs vitamin C, but high doses do not prevent infections. You can get enough from food: peppers, kiwi, citrus, potatoes.

I have anaemia. Should I take iron and vitamins?

In leukemia, anaemia is most often caused by a weakened bone marrow, not by a lack of vitamins. Your doctor will look at your tests and tell you what is needed.

Can I eat spinach? I take warfarin.

Yes, but in roughly the same amount each day. A sudden increase or decrease can change how the medicine works. Tell your doctor.

Should I take vitamin D?

That depends on your blood test. If your level is low, your doctor will set the dose. Taking high doses on your own can be dangerous.

Can I give my child a vitamin syrup?

Not without agreeing it with the paediatric oncologist. Children need different doses, and some vitamins can affect treatment.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. Can I take a multivitamin?

  2. Will vitamin C boost my immunity?

  3. I have anaemia. Should I take iron and vitamins?

  4. Can I eat spinach? I take warfarin.

  5. Should I take vitamin D?

  6. Can I give my child a vitamin syrup?

My questions

12Sources

  1. MedlinePlus (U.S. National Library of Medicine). Vitamins
  2. NHS. Vitamins and minerals
  3. NHS. Vitamins and minerals: B vitamins and folic acid
  4. NHS. Vitamins and minerals: Vitamin K
  5. NIH Office of Dietary Supplements. Vitamin D — Fact Sheet for Consumers
  6. NIH Office of Dietary Supplements. Vitamin B12 — Fact Sheet for Consumers
  7. NIH Office of Dietary Supplements. Folate — Fact Sheet for Consumers
  8. Harvard T.H. Chan School of Public Health — The Nutrition Source. Vitamins and Minerals
  9. Clinical Nutrition (ESPEN), 2022. Berger MM et al. ESPEN micronutrient guideline
  10. Journal of Clinical Oncology, 2020. Ambrosone CB et al. Dietary Supplement Use During Chemotherapy and Survival Outcomes of Patients With Breast Cancer (SWOG S0221)
  11. American Cancer Society. Dietary Supplements: What Is Safe?
  12. World Health Organization (WHO). Micronutrients
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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