B12 absorption drops after 50 — deficiency runs 20–40% in older adults

The recommended daily intake for vitamin B12 is 2.4 micrograms. That is the lowest figure of any vitamin, and the body can store up to 2,500 micrograms in the liver. Most men who eat meat take in around 5 micrograms a day and excrete what they do not need.

On those numbers, deficiency should not happen. Yet 20–40% of older adults are deficient. One study in people over 70 found 22% of men deficient against 8% of women.

Why does it become a problem with age?

The issue is not how much you eat but whether you can free it. B12 in food arrives bound to protein, and separating it takes adequate stomach acid and digestive enzymes such as pepsin. Between 10% and 30% of adults over 50 develop atrophic gastritis — inflammation of the stomach lining — which reduces both.

That creates a genuine exception to the usual whole-foods-first advice. An older digestive system struggles to separate protein-bound B12 from food, while the B12 in fortified foods and supplements is already in free form and skips the step entirely. Hence the recommendation that adults over 50 keep eating fortified foods and consider a supplement.

Which foods contain it?

If you eat animal products: beef, pork, chicken, eggs and seafood are all good sources. Shellfish are unusually dense — two small mussels cover a day's worth. Greek yoghurt and cottage cheese contribute too. One dietitian suggests four palm-sized portions of animal protein a day.

If you are vegan or cutting back on meat, the sources are fortified cereals, fortified non-dairy milks, and nutritional yeast — a cheesy-tasting vegan staple where one tablespoon delivers 100% of the daily dose. Worth knowing: "fortified cereal" is not a specialty product, it is most boxed cereal. Fortification does not make the sugary ones healthy.

What does deficiency look like?

Deficiency is not common, but it is not subtle either. Fatigue and weakness, stomach problems, and a pins-and-needles sensation in the hands and feet are the usual signs. Left alone it can cause megaloblastic anaemia — larger-than-normal red blood cells in smaller-than-normal numbers — bringing fatigue, pale skin, nerve problems and memory loss. Pernicious anaemia, an autoimmune condition that blocks absorption outright, is a separate cause.

How this relates to your strength score

A relative strength score applies a masters correction from age 40, which exists because holding the same numbers genuinely gets harder with age. B12 deficiency quietly makes it harder still: fatigue and weakness eat into training volume, and peripheral nerve symptoms undermine exactly the grip and proprioception heavy loading depends on. If you are past your late forties and see unexplained stagnation alongside persistent fatigue, a blood test is a faster and cheaper check than rebuilding your programme.