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Vitamin B12 after a gastrectomy: why the injections are lifelong | CION Cancer Clinics
After a total gastrectomy, vitamin B12 injections continue for the rest of your life. The stomach made intrinsic factor, the protein that lets the gut absorb B12, and without it neither food nor tablets can get the vitamin in. This page explains why, what the injections involve, what happens if they stop, and how the picture differs if only part of the stomach was removed. CION Cancer Clinics’ surgical oncologists in Hyderabad can talk this through with you.
MI
Medically reviewed by Dr. Mohammed ImaduddinConsultant Surgical Oncologist · MBBS, MS (General Surgery), MCh (Surgical Oncology) · last reviewed September 2026, next review due September 2027
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On this page
- Why do B12 injections have to be lifelong after a gastrectomy?
- What happens in the body when B12 runs low?
- How do the injections actually work, month to month?
- Words you will see on the blood report, in plain language
- Four things families tell us about B12, and what is actually true
- Who this applies to, and what this page cannot tell you
- Common questions about B12 after a gastrectomy
The short answer
Why do B12 injections have to be lifelong after a gastrectomy?
Yes, after a total gastrectomy the vitamin B12 injections are for life. The stomach makes a protein called intrinsic factor, and without that protein the gut cannot absorb B12 from food or from tablets. The stomach does not grow back, so the need does not go away.
What the stomach was doing for you
B12 arrives locked inside meat, eggs, milk and curd. Stomach acid unlocks it, and intrinsic factor carries it to the last part of the small bowel, where it is absorbed. Remove the stomach and both halves of that system go at once. More eggs, more milk or a strong multivitamin does not get round this. The problem is absorption, not intake.
Why nobody feels it straight away
The liver holds a store of B12 that can last a few years. So a person can feel fine for many months after the operation and then slowly become tired, numb in the feet, low in mood or forgetful. By the time the symptoms show, the store is empty. That is why the injections start early and never stop, rather than waiting for a problem.
If you had a partial (subtotal) gastrectomy, the picture is different and is explained further down this page. Ask your surgeon which operation you had before you assume anything.Why it matters
What happens in the body when B12 runs low?
B12 keeps two systems working: the bone marrow that makes blood, and the nerves. Both fail quietly, and the nerve damage can become permanent if it is left too long.
Blood
Without B12 the marrow makes fewer red cells, and the ones it makes are too large. Your haemoglobin falls slowly. You feel tired, short of breath on the stairs, and your family may notice you look pale.
Often the first clue
- A routine blood count with large red cells
- Tiredness that rest does not fix
Nerves
Numbness or tingling in the feet and hands, unsteady walking, and a feeling of walking on cotton. This matters most, because nerve damage left for a long time may not fully recover once B12 is replaced.
Mind and mood
Low mood, poor memory, confusion in older people and a general slowing down. Families often put this down to the cancer or to age, when the cause is a vitamin an injection can replace.
Mouth and tongue
A sore, smooth, red tongue and ulcers in the mouth. These are easy to blame on spicy food or a tooth, so mention them at your follow-up even if they seem unrelated.
Not sure whether this applies to you?
Ask an oncologistIn practice
How do the injections actually work, month to month?
The first course
After the operation the team usually starts with a short run of injections close together to fill the body's store. Your surgeon or physician sets the number and the spacing from your blood results.
The maintenance injection
After that, one injection into the muscle of the arm or buttock at a fixed interval, commonly every two to three months. It takes a minute and stings slightly. A nurse at any clinic or a trained family member can give it once the routine is set.
The blood test
A B12 level and a full blood count at your follow-up visits, so the interval can be adjusted if the level drifts. Do not stop coming for the test because you feel well. Feeling well is what the injection is for.
Keeping it going for life
Put the date in a phone calendar and tell one family member. The commonest reason people become deficient years later is that the injections quietly stopped when a prescription ran out or a doctor changed.
On your report
Words you will see on the blood report, in plain language
- Serum B12 (cobalamin)
- The level of the vitamin in your blood. Low means you need more. A level in the normal range on injections means the plan is working, not that you can stop.
- Intrinsic factor
- The protein the stomach made to absorb B12. After a total gastrectomy you have none, which is the whole reason for the injections.
- MCV
- The average size of your red blood cells. A high MCV is often the first hint of low B12, sometimes before the haemoglobin falls.
- Haemoglobin (Hb)
- The part of the red cell that carries oxygen. A low figure explains tiredness and breathlessness. It has several possible causes after a gastrectomy, and low iron is another one.
- Hydroxocobalamin / cyanocobalamin
- Two forms of injectable B12, both widely used in India. Your doctor chooses the form and the interval.
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Commonly believed
Four things families tell us about B12, and what is actually true
"The level is normal now, so the injections can stop."
The level is normal because of the injections. Stop them and the store drains again over the following years, and after a total gastrectomy the body cannot refill it from food. A normal result means the plan is working, not that you are discharged.
"He is a strict vegetarian anyway, so B12 was always going to be a problem."
Diet and absorption are two separate problems. A vegetarian with a stomach can take a B12 tablet and absorb it. A person without a stomach cannot, however much they eat. Diet matters for iron, protein and weight, but not for this.
"High-dose tablets or a nasal spray will do the same job."
Some studies suggest very high oral doses can be absorbed a little through a different route, and a few centres use them in selected patients. The evidence after total gastrectomy is thin, and the injection remains the standard advice. If your team offers tablets, ask how often they will check the level.
"Feeling tired means the cancer is back."
Tiredness after stomach surgery has many causes, and low B12, low iron and simple under-eating are the common ones. Your follow-up blood tests are designed to sort these out. Do not sit at home fearing the worst when a blood test would settle it in a day.
Being straight with you
Who this applies to, and what this page cannot tell you
Lifelong injections apply with certainty after a total gastrectomy. After a subtotal or partial gastrectomy, where part of the stomach stays, some people keep enough intrinsic factor and some do not. Your team will check the level at follow-up and decide from the result rather than from a rule.
People this page does not fully cover
If you have had an oesophagectomy with a stomach pull-up, a bypass for a blocked stomach, or weight-loss surgery, the absorption picture is different and this page may not fit. If chemotherapy has also left your feet numb, the two causes can be confused, and only your oncologist can separate them.
What this page cannot tell you
It cannot tell you your interval, your form of B12, or whether your own tingling is the vitamin or something else. It does not replace the blood test, which is done with the other follow-up bloods and is usually back the same day.
Bring every prescription and blood report to your follow-up visit, including the ones from a local clinic. It lets the team see whether the injections have actually been given.Questions we are asked
Common questions about B12 after a gastrectomy
Can I take B12 tablets instead of injections?
After a total gastrectomy the standard advice is the injection, because tablets rely on intrinsic factor that you no longer have. Some centres try very high oral doses in selected people with close blood monitoring. If your team suggests that, ask how often the level will be checked. Do not switch on your own.
What happens if I miss one injection?
One missed dose rarely causes harm, because the liver still holds a store. Have it as soon as you can and carry on with the usual interval. What causes trouble is a whole year of missed injections. If you have lost track, tell your team and they will check the level.
Can a family member give the injection at home?
Often yes. It is an injection into the muscle, the same kind used for many vaccines, and a nurse can teach a family member in one visit. Many families in the districts do this to avoid a long journey. Ask your surgeon to write it into the discharge plan.
Does the injection have side effects?
Very few. The site may ache for a day and a small bruise is common. Itching or a rash is rare and should be reported. Some people notice darker urine, which is the harmless colour of the vitamin passing through. Serious reactions are very uncommon.
I had only part of my stomach removed. Do I still need it?
Maybe. Some people keep enough working stomach lining and some do not, and it cannot be predicted from the operation note alone. Your team will check a B12 level at follow-up, usually more than once, and start injections if it drifts low. Ask for the result each time rather than assuming it was fine.
Will the injection help my tiredness quickly?
If low B12 is the cause, most people feel the difference within a few weeks as the marrow catches up. If nothing changes, the tiredness has another cause, and low iron, poor intake and the general recovery from a big operation are the usual ones. Say so at your visit so the next test can be done.
Is the injection covered by Aarogyasri or insurance?
The vial itself is inexpensive and is widely available at government health centres and pharmacies. Follow-up blood tests are often covered when they form part of an approved cancer care plan. Call the helpline with your scheme or policy details and we will check what your own cover includes before you travel.
Will I need the injections even after I am declared free of cancer?
Yes. The injection has nothing to do with the cancer. It replaces a job the stomach used to do, and the stomach is not coming back. People are often surprised years later when a new doctor asks why they still have it. Keep a note of the reason with your discharge papers.
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Sources
- NHS — Vitamin B12 deficiency: treatment
- Macmillan Cancer Support — Surgery for stomach cancer
- Cancer Research UK — Surgery for stomach cancer
- American Cancer Society — Surgery for stomach cancer
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Iron and Calcium Deficiency After GastrectomyThe other two things that run low, and why tiredness is not always B12Follow-Up After GastrectomyWhen the blood tests happen and what each visit checksTotal vs Subtotal GastrectomyWhich operation you had decides whether the injections are certainLife One Year After GastrectomyWhat settles, what stays, and the routines that carry on
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Not sure whether the injections were ever started?
Send us the discharge summary and the latest blood report. A surgical oncologist will check what has been done and what needs to happen next. One helpline serves every CION centre.