Epidemiology
A study in the year 2000 indicates that B12 deficiency is far more widespread than formerly believed. The study found that 39 percent of studied group of 3,000 had low values. This study at Tufts University used the B12 concentration 258 pmol/l (= 350 pg/mL) as a criterion of "low level". However, a recent research has found that B12 deficiency may occur at a much higher B12 concentration (500–600 pg/mL). On this basis Mitsuyama and Kogoh proposed 550 pg/mL, and Tiggelen et al. proposed 600 pg/mL. Against this background, there are reasons to believe that B12 deficiency is present in a far greater proportion of the population than 39% as reported by Tufts University.
In the developing world the deficiency is very widespread, with significant levels of deficiency in Africa, India, and South and Central America. This is theorized to be due to low intakes of animal products, particularly among the poor, though data from WHO publications on world food consumption point to a large deficiency of poor populations in consuming adequate amounts of fresh fruit and vegetables, which carry B12 from bacteria in the soil they are grown in, so this is likely a primary cause as well, since vitamin B12 does not originate from animal sources and can be obtained without consuming animal products.
B12 deficiency is more common in the elderly. This is because B12 absorption decreases greatly in the presence of atrophic gastritis, which is common in the elderly.
A 1982 American study found that among 83 volunteer subjects, 92% of the vegans, 64% of the lactovegetarians, 47% of the lacto-ovovegetarians, and 20% of the semivegetarians had serum B12 levels less than 200 pg/ml. "However," the researchers said, "their complete blood count values did not deviate greatly from those found for nonvegetarians, even though some had been vegans or lactovegetarians for over 10 years. Macrocytosis among the vegetarians was minimal; none had a mean corpuscular volume greater than 103 fl."
The 2000 Tufts University study found no correlation between eating meat and differences in B12 serum levels.
Read more about this topic: Vitamin B12 Deficiency