不是放多了，而是你想的太多了。五十岁以上的，对口服B12吸收减少。有时靠打肌肉才能维持

https://www.webmd.com/vitamins/ai/ingredientmono-926/vitamin-b12

Because 10% to 30% of older people do not absorb food-bound vitamin B12 efficiently, those over 50 years should meet the RDA by eating foods fortified with B12 or by taking a vitamin B12 supplement. Supplementation of 25-100 mcg per day has been used to maintain vitamin B12 levels in older people.