All B-vitamins are water-soluble and leave the body in the urine. It is necessary to consume them daily.
People can obtain vitamin B-12 from animal foods such as meat and dairy. Those concerned that they may be deficient can take a supplement. B-12 deficiency usually develops in older adults and people who follow a vegan or vegetarian diet.
The Office of Disease Prevention and Health Promotion advise an Adequate Intake of around 2.4 mcg per day. Check with a doctor before trying supplements, as some can interfere with the effects of medication.