Following on from the practice decision to move the appropriate patients receiving B12 injections to oral B12 tablets we have received several questions from patients which we have answered below.
Due to the number of patients involved we cannot contact everyone individually, but many of the questions being asked are similar. We have therefore put together some common questions and answers for you.
Q) Will supplements work as well as the injection?
A) This is our most frequently asked question. All of the patients contacted have started on B12 injections and have received the loading doses that are administered close together. Approximately 50% of the loading dose is stored in the liver for the body to use up slowly when needed. The 3 monthly injections therefore are just top ups. In other words you have plenty of B12 from the injections you have already received to last many months. There is no clinical evidence to say injections work better than tablets. Current evidence suggests the tablet will work just as well within the body, which will continue to absorb the B12 just as it does from the injection.
Q) I cannot absorb B12 so tablets won’t work for me
A) B12 is the largest of the vitamin molecules. We don’t make it – it has to be obtained from the diet. Patients are almost all aware that B12 mainly gets into our body because of a ‘carrier’ called intrinsic factor (IF). This IF binds to B12 and takes it into the blood.
HOWEVER there is another 5% which is absorbed without IF. Often the Intrinsic Factor, or lack of, is blamed for the deficiency when in fact we simply do not get enough from the average modern diet. If an average diet contains only 1 – 4 mcg it is hardly surprising we see so many people who are deficient. Historically, when we prescribe oral B12 we prescribe a dose of 50mcg per day. Through this challenging time, and to ensure all patients maintain adequate B12 blood levels, we have prescribed 1,000mcg tablets daily – that is 400 times that normal recommended amount. Even patients who do not have Intrinsic Factor will absorb enough for their daily recommended minimum amount from such a large dose. There is no danger of overdose as the body will naturally dispose of excess in the urine.
Q) I have pernicious anaemia
A) Some patients will have had a diagnosis of pernicious anaemia. The loading doses which everyone has to begin with have effectively treated the pernicious anaemia, by flooding the body with B12, 50% of which is stored in the liver and used up as required. The 3 monthly injections which follow are simply a precaution to stop the pernicious anaemia coming back. As stated, the initial loading dose will have created sufficient levels and stores to take us though this difficult time without ill effect.
Q I know when I need my next injection because I start to feel ill and when I get it I feel so much better.
A: People who receive injections often make this comment however it can be explained. When the 1mg injection is administered into the muscle the B12 is released into the bloodstream, in theory, over 3 months, HOWEVER, people vary in the amount of muscle and the density of that muscle. Although it does go into the bloodstream only the B12 that the goes on to bind to body protein will stay in the body. As a B vitamin it is very easily lost. In other words, with the injection, vitamin B12 levels vary considerably throughout each 3 month period which means people may well be justified in their belief about how they feel before their injection: ‘I just know when I need it’. Taking the tablet at this mega dose will ensure consistent blood levels through this time period, even in those with poor/low absorption levels, indeed they may feel they no longer experience the effect. This may be why many areas are considering oral megadose over the traditional injection once the loading doses have been completed. Your vitamin B12 levels can vary considerably between each 3 monthly injection, being high just after and lower just before, which can create this effect of ‘just knowing when you need it.’ By giving you a very high oral dose every day we eliminate this ‘up and down’ effect so you will not feel like this and should just feel normal all the time.
Page last updated: 20 July, 2020