What is the best source of vitamin B12?

Clams and beef are high in vitamin B-12, according to Good Housekeeping. Meat, poultry, eggs, seafood and dairy products are all food sources that supply an adequate amount of B-12, according to WebMD.

Vegans who do not eat animals or animal byproducts as well as people with medical conditions that limit nutrient absorption often have problems maintaining adequate B-12 levels, as stated by WebMD. A simple blood test is available to check for B-12 deficiency. Vitamin B-12 helps in the production of DNA and red blood cells. Symptoms of a deficiency include weight loss, rapid heartbeat, pale skin, weakness, easy bruising and bleeding and lightheadedness.