A team of researchers from St. John’s Research Institute (SJRI) has developed a new test to measure vitamin B12 absorption in humans with stable 13C isotopes. Earlier, this was possible only using the radio-isotopes-based Schilling test.
This major clinical development has been published in American Journal of Clinical Nutrition.
Vitamin B12 deficiency, that is widespread in India, is linked to many poor health outcomes. It is mainly due to a low intake of animal source foods or malabsorption. The problem lies in measuring whether it is well absorbed from the diet or from remedial supplements. Unless the absorption is known, it is very hard to design the appropriate dose to remedy deficiencies.
Sarita Devi from St. John’s Research Institute, who is the lead author of the paper, said unfortunately, the measurement of vitamin B12 absorption is not performed now, because the original or modified Schilling’s test requires radioisotopes. “The problem is the use of radioactive isotopes (Cobalt in this case), which is heavily restricted, to ‘label’ vitamin B12 so that it can be traced to quantify its absorption. This problem has continued for the last 70 years, since Dr. Schilling first published his eponymous testing method,” she explained.
The study describes the re-engineering and innovation of a new method to measure Vitamin B12 absorption. “We did this by biosynthesizing a novel Vitamin B12 molecule that was labelled with a ‘stable isotope’ of carbon 13C. This, as the name implies, is stable (not radioactive and therefore does not emit any harmful radiation) and is therefore safe for human use,” she said.
The molecule that the team of researchers synthesized, is a form of Vitamin B12 called 13 C-cyanocobalamin. This (cyanocobalamin) is one of the commercial vitamin B12 supplements that are prescribed. “We then used this to measure vitamin B12 absorption in humans, and also defined a new mathematical or pharmacokinetic model for this purpose. This test is safe and can now be used in a clinic and in any age group safely without radiation concerns,” Dr. Devi explained.
“This is a major development in nutrition that also changed the daily requirement of Vitamin B12 in a recently published report by the ICMR-National Institute of Nutrition for Indians,” she said. Anura V. Kurpad, senior author of the paper and chair of the ICMR Expert Committee on Nutrient Requirement of Indians, said the earlier thinking was that dietary vitamin B12 was 100% absorbed.
As the researchers’ team led by Dr. Devi had measured this at about 50% absorption, Dr. Kurpad said: “This effectively doubled the daily dietary requirement from 1 microgram to 2 microgram/day. Since Vitamin B12 is only available from animal source foods, it is critical to ensure that an adequate intake of milk or eggs/meat is available in the diet.”
From a therapeutic viewpoint when treating the deficiency, the study also showed that the absorption of Vitamin B12 was very tightly regulated, in that it could not go above a certain amount. Hence, a high intake does not necessarily mean more absorption, she added.