What you will notice

First week or two: energy begins to lift and a sore tongue settles, and this is the fastest, clearest signal. Weeks two to four: the fog clears further, sleep and mood steady, and the heaviness on stairs eases as the blood count starts to climb. Weeks four to eight: blood counts normalise, and if you are measuring, homocysteine and methylmalonic acid come down. Longer, three to twelve months: tingling and numbness in the feet and hands retreat slowly from the toes inward, which is the slowest and most valuable change, and after that the job becomes keeping the level topped up rather than refilling it.