Some people have trouble properly absorbing vitamin B12 because of GI/digestive issues and underlying health conditions
GLP-1 receptor agonists for major cardiovascular and kidney outcomes in type 1 diabetes
Number two, your protein intake

Deboned chicken, chicken meal, lentils, peas, oatmeal, sun-cured alfalfa meal, pearl barley, natural chicken flavour, chicken fat (preserved with mixed tocopherols and citric acid), choline chloride, pea fiber, potassium chloride, fish oil, taurine, freeze-dried chicken, inulin, yeast extract, salt, zinc proteinate, DL-methionine, L-lysine, dried apples, dried blueberries, dried carrots, dried cranberries, dried pumpkin, ground ginger, iron proteinate, L-carnitine, L-ascorbyl-2-polyphosphate, vitamin E supplement, Yucca schidigera extract, niacin supplement, manganese proteinate, dried Bifidobacterium bifidum fermentation product, dried Enterococcus faecium fermentation product, dried Lactobacillus acidophilus fermentation product, dried Lactobacillus casei fermentation product, sunflower oil, copper proteinate, D-calcium pantothenate, vitamin A supplement, menadione sodium bisulfite complex, riboflavin supplement, canola oil, thiamine mononitrate, vitamin B12 supplement, biotin, pyridoxine hydrochloride, sodium selenite, calcium iodate, folic acid, vitamin D3 supplement, rosemary extract

Modulation of oxidant stress in vivo in chronic cigarette smokers