Spring 2014 True Natural Health Magazine – Your Questions Answered
By Roger French



You ask four questions:

  1. How do we know if we are lacking the IF?
  2. If a person is lacking it, what action can he/she take to remedy this?
  3. Does vitamin B12 need to bind with the IF just to get through the stomach acid or does B12 need the IF to be absorbed?
  4. Can the B12 manufactured by gut bacteria in the small intestine be absorbed?



The best way to answer the above is to explain how IF works in the assimilation of B12.

In the early 1900s, vitamin B12 was called the ‘extrinsic factor’. The early investigators could not understand how in some cases there could be abundant B12 in the diet, yet still have deficiency, so they called it ‘pernicious’ anaemia. The mysterious something that was needed for it to be absorbed was given the name ‘intrinsic factor’ – and these names have stuck.

In food, B12 is bound to protein, and in the stomach the hydrochloric acid splits it off to give free B12. The stomach mucous lining secretes IF which combines with B12 to form IF-B12 complexes. In this way, the IF protects B12 from digestion as it passes through the stomach and duodenum. In the small intestine in an alkaline environment and in the presence of the mineral calcium, the B12 is split off from the complexes, absorbed into the bloodstream and transported to the liver. The IF remains in the bowel and is eliminated.

Without the IF, only about 1% of B12 is absorbed, which is so little as to be virtually useless – except in the case of massive doses of supplements.


Deficiency of IF can be due to:


Even when there is abundant IF, absorption of B12 may be compromised by:


If IF is deficient, symptoms of deficiency of B12 will develop slowly, but if there are small intestine problems, it can develop relatively rapidly – possibly in a matter of months.

B12 is stored in the liver, where there can typically be around three years supply.

In spite of the above points, it is possible to have adequate B12 in the bloodstream without depending on dietary sources, which are almost entirely animal products. This is because the ‘friendly’ gut bacteria manufacture it. Studies of people on vegan diets – who have no significant B12 in their diets – have often, though not always, been found to have adequate levels of B12. This virtually confirms that the vitamin that these bacteria make can be absorbed, without the IF being involved.

Plant sources of B12 are almost always analogues that the body cannot use, so we essentially depend on animal food sources or our friendly gut bacteria. If neither of these supply enough, then supplements, which fortunately are quite effective, become essential.

How do we know if our bodies have adequate levels of B12? A blood measurement is not the best indicator because it gives no indication of the body’s reserves. Better indicators are levels of homocysteine and methyl-malonic acid (MMA), which depends on B12 for its production. Researchers have concluded that having normal levels of both methyl-malonic acid and total homocysteine make it virtually certain that there is no significant B12 deficiency.


It’s time to summarise this subject in the form of answers to your questions.

How do we know if we are lacking the IF?

As far as I know, the most practical way is by having adequate sources of B12 in the diet and if there is still deficiency, it is highly likely that IF is lacking.

However, I believe that doctors can administer ‘exogenous’ intrinsic factor, and if this improves B12 levels, it indicates IF deficiency.


If a person is lacking IF, what action can he/she take to remedy this?

In most cases of deficiency, the only solution is the medical solution, which is B12 injections, normally once a month. Persons with severely low levels of B12 may need more shots in the beginning.

However, some people may overcome the deficiency by taking B12 supplements by mouth in very large doses. Whereas, the daily requirement is 1 – 2 micrograms, very large doses means between 100 and 100,000 micrograms.  


Does vitamin B12 need to bind with the IF just to get through the stomach acid or does B12 need the IF to be absorbed?

It apparently needs the IF for delivery right to the absorption cells in the walls of the small intestine.


Can the B12 manufactured by gut bacteria in the small intestine be absorbed?

As stated above, the indirect evidence from vegan diets is that it must be possible. Further, researchers have found that there is a pathway by which B12 can be absorbed in the absence of IF.


If you want to read more about vitamin B12 itself, there is a discussion of B12 and vegetarian diets in the Winter 2013 issue of True Natural Health, pages 32 – 24.