One of the causes that can lead to a deficiency in vitamin B12 is infection with H Pylori. H Pylori is known for contributing to gastritis and ulcers but due to its effect on the cells in the stomach it also prevents proper absorption of vitamin B12 contributing to a deficiency in this substance.
PCC Natural Markets explains this on their website, "Infection with Helicobacter pylori, a common cause of gastritis and ulcers, has been shown to cause or contribute to adult vitamin B12 deficiency. H Pylori has this effect by damaging cells in the stomach that make intrinsic factor - a substance needed for the normal absorption of vitamin B12. In one trial, H Pylori was detected in 56% of people with anemia due to vitamin B12 deficiency. Successful eradication of H Pylori led to improved blood levels of B12 in 40% of those infected. Other studies have also suggested a link between H Pylori infection and vitamin B12 deficiency. Elimination of H Pylori does not always improve vitamin B12 status. People with H Pylori infections should have vitamin B12 status monitored." (http://www.pccnaturalmarkets.com/health/Supp/Vitamin_B12.htm)
The Archives of Internal Medicine Vol 160, No 9, May 8 2000 tells of a study done to determine the effect of H Pylori on Vitamin B12, "We performed a prospective cohort study involving 138 patients who had anemia and vitamin B12 deficiency. An upper gastrointestinal endoscopy was performed to assess the severity of atrophic gastritis and biopsy specimens for Campylobacter-like organisms tests and histological examination for H Pylori were obtained at the time of diagnosis. The diagnosis of H Pylori prompted a combination treatment." (K, Kaptan, MD, et al. Arch. Intern. Med. 2000; 160:1349-1353)
They later go on to say that "Helicobacter pylori was detected in 77 (56%) of 138 patients with vitamin B12 deficiency and eradication of H Pylori infection successfully improved anemia and serum vitamin B12 levels in 31 (40%) of 77 infected patients." (K, Kaptan, MD, et al. Arch. Intern. Med. 2000; 160:1349-1353)
It can therefore be seen that H pylori infection definitely has an effect on vitamin B12 deficiency. Studies have shown that the damage H Pylori does to the stomach cells prevents proper absorption of vitamin B12, leading to vitamin B12 deficiency. Some studies seem to indicate that by removing the H Pylori that this could also help to improve vitamin B12 levels although this is still being debated. If you suffer from H Pylori infection then it is recommended that you have your vitamin B12 levels checked regularly to ensure that you are still getting sufficient vitamin B12 to meet your daily needs.