source of vitamin b12

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Why you might be low: B12 is found primarily in animal products, so if you're a vegan or vegetarian, you may not be getting enough. But diet isn't the only cause of low B12. Proton pump inhibitors, or PPIs, used to treat heartburn, are associated with inadequate levels of this B vitamin, says Caren Behar, MD, a clinical associate professor of medicine at NYU Langone's Joan H. Tisch Center for Women's Health. "It's become a common cause of low B12."

Why you need it: It's essential for good neurological function and red blood cell formation (the cells that carry oxygen around your body). That's why, if you're low, you can feel lethargic and mentally foggy.

Where to find it: The seafood aisle is a great place to start, since haddock, salmon, tuna and trout are high in B12. Milk, yogurt and cheese are also good sources. If you're vegan, many breakfast cereals are fortified with 100 percent of your daily recommended B12—just keep an eye on how much sugar they're packing too.