Some things never change. My daughters still think I drive too slowly. Yet some things do change, especially in the field of nutrition. For example, we used to think that deficiencies of vitamin B-12 were rare except among strict vegetarians or people with an autoimmune disease called pernicious anemia.

New evidence now indicates that if you’re on this list, you may be at risk for a B12 deficiency: 50 years or older (we can lose the ability to absorb vitamin B12 as we age), vegetarian or vegan (B12 is not found in plant foods), take metformin (a diabetes medication that can reduce the body’s ability to absorb B12), have any type of intestinal disorder or stomach surgery such as gastric bypass (vitamin B12 needs a well-functioning gut to be absorbed), take anti-acid medicines or aspirin, ibuprofen or similar types of pain relievers (some meds can reduce the effectiveness of stomach acids to digest and absorb B12).

Although it is only required in micro amounts, vitamin B-12 is vital to the formation of healthy red blood cells and it helps build everything from genetic material (DNA) to hormones and other proteins. Perhaps most notable is B12’s role in our nervous system — all the pathways that help us to think, move and speak. A deficiency of vitamin B12 can cause the brain to malfunction and lead to dementia, for example.

Vitamin B-12 (also known as cobalamin because it contains the mineral cobalt) also helps keep our homocysteine levels in check. High amounts of homocysteine are associated with inflammation that can lead to heart disease.

For most of us, the most reliable sources of B12 are animal foods including fish, poultry, meat, eggs, milk, cheese, and yogurt. Just 3 ounces of cooked clams, for example, provides more than a thousand times our recommended intake of vitamin B-12, according to the USDA Nutrient Database.

Other reliable sources include B12 supplements or fortified foods such as cereals and nutritional yeasts. People with pernicious anemia or other disorders that prevent them from absorbing vitamin B12 in the stomach may need to rely on regular injections of this important nutrient directly into the blood stream.

How much vitamin B12 we need in a day may also be changing. New evidence suggests the current recommendation may be too low to accomplish all its vital functions.

In the meantime, here is a hint when talking to your doc about testing your vitamin B-12 levels. Blood tests for vitamin B-12 may not tell the whole story, according to recent research. According to the National Institutes of Health, additional laboratory tests which include homocysteine and methylmalonic acid values may also be needed to reliably detect low levels of vitamin B-12.