Is low B12 connected to Colon/Bowel/Rectal cancer?


My names Arron. I'm a 24 year old male.  Normal BMI.

As the above implies, i am just wondering about the connection between vitamin b12 and the above cancers?  I recently went to my GP due to there being quite a lot of blood when I empty my bowels, both in the toilet and on the tissue; not so much incorportated within the stool.   The doctors sent me for bloods and referred me to get a colonoscopy however the wait for this is 12 weeks.  I received my blood results back today and the doctor seemed confused to my results.  She mentioned that my B12 is as low as 50 but all my other levels are fine.  She was baffled due my only deficiency being B12.   She mentioned that my Folic levels were a little bit down but nothing to be concerned with however she has referred me for further blood tests to rule out any anomolies.  

As you can imagine, I got home asap and googled the above cancers in connection to B12 and got so many different answers, I didnt know where to turn.

Please will you answer me this -

Is low B12 connected to connected to digestive cancer?

Should I be concerened?

How should I move forward?


Thank you in advance! :)

  • Hi arroncraig. Welcome to the forum.

    I'm not a doctor, however I'm going break my own rule and diagnose you with the disease of HyperGoogleItis. Also known as too much Googling. 

    To answer your specific question, there is a possible link between low B12 and digestive cancer, but that is only half the story.  The risk of digestive cancer at age 24 is very low, and so all the reduced B12 might do is increase that very low risk ever so slightly.  Resulting in a risk that is still very low. If I were in your situation and at your age, I would not be unduly concerned. 

    Unfortunately, these are nuances that can be missed when consulting with that quack Dr Google, which is why most of here know when to lay off Google.  

    So, the best you can do for now is stop Googling, try to keep calm and get on with your life as normal. The doctor may well refer you for more tests, and the colonoscopy might or might not show anything useful.  I'm afraid you just have to go with the flow for now. 

  • Telemando is dead right about google but b12 needs sorting out dont panic though b12 is genraly absorbed in your terminal ilieum were your small bowle connects to your large bowle and stored in your liver 

  • Thank you, you have some what put my mind at ease.  I’m laying off google for time being because it is adding to the stress. Haha


    Thank you for taking the time to reply! :)

  • hi 


    I’m the same as you did you find out what it was? 



  • Hi Arron

    I have B12 deficiency too. It can have multiple causes. Such as an auto-immune disorder called pernicious anemia, some prescribed drugs such as metformin cause it, inadequate B12 in the diet and celiac disease (severe gluten allergy).  I have also had GI bleeding but it was not necessarily connected with B12 deficiency but caused by a duodenal ulcer. Your young age does not exclude the possibility of these issues.

    Your doctor should refer you to a consultant at the hospital with your symptoms and with no obvious explanation for the GI bleeding. You should insist that you are referred to a GI specialist. If the blood is bright red it may be simply caused by haemorrhoids but you should be diagnosed by a specialist. 

    Whatever the cause of your B12 deficiency you must receive corrective treatment immediately. If your doctor will not provide it with blood levels as low as 50 that is a cause for concern. You must immediately request B12 treatment. This should be a series of injections over several weeks and then about every 12 weeks once your levels have been corrected. The exact cause may never be found but blood tests can diagnose pernicious anemia.

    The combination of symptoms may indicate celiac. The best thing is to keep eating wheat products and to request your GP tests you for it. If the test is positive further investigations will be triggered and you must attend them, as celiac can after many years cause cancer if you continue to eat gluten. 

    The hospital consultant should also test you for parasites as some can cause b12 deficiency and GI bleeding.

    None of this is intended to be alarmist. Your symptoms are not minor. They may however be unconnected. As for cancer risk from B12 deficiency. Yes there is a link but usually over a very long time period in which the B12 deficiency was not fully corrected or was left untreated. It causes high levels of homocystein in the body and that encourages cancer, although I think studies are limited to only a few cancers. 

    To help yourself please get treated right away for the B12 deficiency (by the GP) and get diagnosed by the hospital consultant. If you have a baffled 9ne already then ask for a second opinion from another one. Eat lots of greens, preferably in the form of salads and smoothies, you can mix in fruit to make it more palatable. The folate in greens will help you to absorb and utilise B12. B12 deficiency also causes nerve damage and severe fatigue. If you do not have treatment this can become irreversable. 

    You will feel so much better with treatment and the care of a good GI consultant. Good luck.



  • Hi, I’m worried as being diagnosed with pernicious anaemia by my gp in 2000 I was told I would need b12 injections for the rest of my life. In 2015 I was at a different surgery where I was refused b12 and told unnecessary . Same year I was diagnosed with breast cancer and now how secondary breast cancer which is incurable. My oncologist had to stop my palliative chemo due to to low platelets and has now put me on b12 . I’m 64 now and worried all the years without b12 have caused the cancer . Thanks in advance .