Vitamin B12 is involved in nervous system functioning, energy metabolism, blood cell formation, and other body functions. If you follow a vegan or vegetarian diet, you may be at increased risk of a B12 deficiency, since the main food sources of vitamin B12 include meat, fish, poultry, eggs, and dairy products, and you will likely benefit from a supplement. Older adults may also be at risk of vitamin B12 deficiency, because it is common to have a decreased ability to absorb this vitamin. Some brands we like include Thorne Research, Pure Encapsulations, and Nature Made.