Why do B12 pills contain 1000µg, since we need 2.4µg/day ?
I read that you absorb 10µg of a 500µg pill.
Do you absorb 1µg of a 50µg pill?
Do you absorb 10µg of a 10µg pill?
I think the numbers vary due to differences in absorption per individual. Different people may have different absorption rates.
Although we need very little B12 (sometimes we can go for many years without needing a B12 supplement) we still take (larger) amounts that are proven to work - to be on the safe side.
Current recommendations by Nutrition facts is that average adult should take around 2000µg/weekly or 50µg/daily of B12 in a form of cyanocobalamin.
Personally, I'm taking around 2500µg pill once a week and every time I tested my B12 levels they are on the higher side but still within recommended norms.
I believe that the recommendations are based on research and scientific evidence (that are usually listed as links on nutritionfacts website).
This may not be the ultimate truth as we're still receiving a new data.