If you’re depending on food to supply your vitamin B12, and you’re over 50, there’s a good chance you’re going to end up with a B12 deficiency. It doesn’t matter if your diet includes plenty of animal food. It’s not intake that’s the problem, it’s absorption. An older body is not the same as a younger body. Grey hair and muscle loss we can see; dwindling ability to absorb certain nutrients is invisible.

Dr. Lindsay Allen from the University of California, Davis, writing in the AJCN, says:

How Common Is Vitamin B-12 Deficiency?, Lindsay H Allen, American Journal of Clinical Nutrition (AJCL), February 2009

Vitamin B-12 deficiency and depletion are common in wealthier countries, particularly among the elderly. … The 2 main causes of vitamin B-12 deficiency are inadequate dietary intake and, in the elderly, malabsorption of the vitamin from food. Contrary to popular belief, not only strict vegetarians (vegans) are at high risk of vitamin B-12 deficiency, and there is strong evidence that status reflects usual intake across a wide range. … Malabsorption of vitamin B-12 from food is the main cause of deficiency in the elderly and explains why depletion occurs with aging.

Vitamin B12 follows a rather circuitous path to absorption. First, of course, you have to eat it. Then you have to free it from the proteins to which it’s bound, so you need a healthy amount of stomach acid. Stomach acid levels decline as we age. They’re also affected by drugs like antacids which are taken for gastric conditions that occur more frequently in the elderly. Once the vitamin is freed, it must bind to a specific protein called Intrinsic Factor (IF) which is secreted by cells that line the stomach. That’s a major stumbling block right there. Anything that damages those parietal cells will cause outright B12 deficiency. (Some people don’t secrete much IF to begin with.) Like? … Ulcers, tumors, scar tissue from ulcers & tumors, any kind of inflammation or gastritis, alcohol intake, and, naturally, the removal of these cells through weight loss or cancer surgery. Intrinsic Factor also doesn’t bind well in an acidic environment. Remember we needed an acidic environment, a low pH, to release B12 from its protein source? Well, now we need a higher pH, about 7, for binding. The pancreas releases buffers to raise the pH of gastric juice. Anything that interferes with pancreatic secretion (diabetes, cancer, cystic fibrosis, etc.) will interfere with B12 absorption. Right, now the IF-B12 complex travels to the small intestine where it’s absorbed. B12 needs to be freed from IF. The pancreas would have secreted enzymes to do that. No enzymes? Poor absorption. Finally it gets absorbed. Any damage to the lower part of the small intestine (celiac disease or other gluten-induced damage, cancer surgery, scar tissue, overrun by bacteria from the colon) will result in poor B12 absorption.

Given all these potential roadblocks, it’s a wonder we get any B12 into us at all.  Many of us struggle. Dr. Allen, citing the Framingham Offspring Study, says that between 4%-6% of US adults over 40 are outright deficient.  But a lot more suffer with low levels:

Marginal depletion (serum vitamin B-12: 148–221 pmol/L) was more common and occurred in ≈14–16% of those aged 20–59 y and greater than 20% of those older than 60.

Over a quarter of older Americans are coping with B12 depletion or full-blown deficiency! Why is this problem coming to the fore now?

This prevalence was underestimated in the past for several reasons, including the erroneous belief that deficiency is unlikely except in strict vegetarians or patients with pernicious anemia, and that it usually takes ≈20 y for stores of the vitamin to become depleted.

Absorption rates are higher for B12 that is not food-bound. And you don’t need much, just 1 or 2 micrograms. Any more and the receptors get overloaded, the rest passes out with stool:

In older persons, food-bound cobalamin malabsorption becomes the predominant cause of deficiency, at least in part due to gastric atrophy, but it is likely that most elderly can absorb the vitamin from fortified food.

Plasma vitamin B-12 concentrations plateaued at intakes greater than 10 μg/d in the Framingham Offspring Study. … Although greater than 70% of the vitamin is absorbed when intake is in the range of 0.1–0.5 μg, the ileal receptors for the vitamin B-12–intrinsic factor complex become saturated with higher intakes such that absorption falls to ≈50% of a 1-μg dose, 15% of a 10-μg dose, and 3% of a 25–50-μg dose. … About 1% of a high dose will be absorbed by passive diffusion, independently of gastric function or intrinsic factor.

Look at that. Just 3% of a 25 microgram dose gets absorbed. It’s hard to find a B12 supplement under 500 micrograms! It’s a case of “value-added.” They can charge more, but you don’t get more.

My opinion… If you’re over 50, even if you don’t believe in taking supplements, take vitamin B12. Don’t rely on food. Eating meat won’t cure a deficiency. This is one time where the government’s National Institutes Of Health is right:

“Adults older than 50 years [should] obtain most of their vitamin B12 from vitamin supplements or fortified foods.”