Getting Enough Vitamin B12

Published: April, 2015

By: Linda Antinoro, R.D., L.D.N., J.D., C.D.E.

Vitamin B12 is vital for the body to produce healthy red blood cells. It also is needed for proper nerve function and DNA synthesis.

Vitamin B12 deficiency occurs when there are low levels of stored B12 in the body. This can lead to:

  • Anemia
  • Fatigue
  • Weakness
  • Soreness of the mouth and tongue
  • Constipation
  • Decreased appetite
  • Weight loss
  • Numbness and tingling in the hands and feet
  • Dizziness, light-headedness
  • Poor memory and confusion

Unfortunately, more people are at risk for deficiency. Here's why.

1. Aging

As we age, our stomachs produce less gastric acid. This condition is called atrophic gastritis. It reduces the body's ability to absorb vitamin B12 that's bound to protein in foods. Synthetic B12, which is found in fortified foods and supplements, doesn't require stomach acid for absorption. To avoid deficiency, the Institute of Medicine and the Dietary Guidelines for Americans recommend that people 50 and older eat B12-fortified foods or take a supplement.

2. Certain medications

Medications for indigestion and reflux work by shutting off gastric acids. These include proton pump inhibitors (PPI), such as esomeprazole (Nexium), omeprazole (Prilosec) and lansoprazole (Prevacid), and histamine-2 receptor agonists (H2RAs), such as famotidine (Pepcid) and ranitidine (Zantac). With less stomach acid, the body can't absorb as much B12.

In one particular study, people taking PPIs for more than 2 years were 65% more likely to be deficient in vitamin B12. Interestingly, the strongest association was among those younger than age 30.

Metformin, a hypoglycemic agent taken by some diabetics, may also reduce the absorption of B12 by possibly altering intestinal motility. In a randomized, placebo-controlled trial, patients with type 2 diabetes who took metformin for 4.3 years had vitamin B12 levels that were 19% lower than B12 levels of people who took a placebo. This raised the risk of B12 deficiency by 7.2%.

3. Gastrointestinal disorders or past gastrointestinal surgery

People with certain medical conditions, such as celiac disease and Crohn's disease, may be unable to absorb adequate B12 from food.

Surgery to remove part or all of the stomach can also result in the inability to absorb this vitamin.

4. A vegan diet

Vegans (strict vegetarians who do not eat any meat, fish, egg or dairy products) can develop vitamin B12 deficiency because they lack vitamin B12 in their diets. There are no known plant foods that are natural sources of B12. Fortunately, eating fortified foods, such as breakfast cereals, soy milk and vegetarian meat substitutes, can help prevent a potential deficit. However, research shows that vegans who don't take a B12 supplement often have inadequate B12 levels.

How Much Dietary B12 Do I Need?

A blood test can determine your B12 levels. Depending on the laboratory, a normal range is anywhere between 200 to 900 picograms per milliliter (pg/ml). Most experts agree that values less than 200 pg/ml make up a B12 deficiency. Others say that a blood level of at least 350 pg/ml is optimal.

The recommended dietary allowance (RDA) for adults is 2.4 micrograms (mcg) a day. (Women who are pregnant or breastfeeding need more.) Some nutrition experts question if this amount is enough, especially among the elderly. The U.S. Food and Drug Administration sets the Daily Value (DV) for vitamin B-12 at 6 micrograms. (The DV is found on Nutrition Facts labels on some foods.) People at risk for deficiency probably will benefit from more than 2.4 mcg. There's no official upper limit for B12 intake so toxicity or overdoing is not a concern. Only people with Leber's disease, a hereditary eye condition, should avoid supplemental B12.

Best Sources of B12

B12-fortified foods are a good way to get enough of this nutrient, especially if your diet is low on animal foods, such as meats, fish, poultry, milk, cheese and eggs. Some foods are better sources of B12. In a large population-based study, milk and fish were better sources of B12 than meat and eggs were. Dairy foods especially are a highly "bioavailable" source of the vitamin. Vitamin B12 in meat may be less bioavailable due to losses during cooking and the presence of collagen, which isn't digested as well with decreased gastric secretion.

Supplements can make up for lack of dietary B12. They come in several forms: capsules, tablets that dissolve under the tongue (sublingual), nasal gels and injections. A single daily supplement (capsule or tablet) will generally have between 25 mcg and 1,000 mcg. A multivitamin formulated for adults over age 50 usually supplies 25 mcg. Separate B12 supplements often contain a much higher dose, but only a small amount gets absorbed.

Food Source

Amount (micrograms)

Breakfast cereal (3/4 cup)*


Soy milk (8 oz)


Salmon, Atlantic, wild, cooked (3 ounces)


Turkey breast, roasted (3 ounces)


Yogurt, nonfat (1 cup)


Beef tenderloin, broiled (3 ounces)


Vegetarian meat substitute (1 patty)


Milk, nonfat (8 ounces)


Egg, medium (1)


Items in bold are sources of synthetic B12.

*Fortified cereals have between 25% to 100% DV.

The Bottom Line

It is reasonable to ask your doctor to check your B12 level. If it is within normal range, aim for at least the RDA amount, and ideally, the DV of 6 mcg. Routinely including B12-containing foods in your diet, along with some B12-fortified foods, will put these numbers in reach. If you are in one of the risk groups for B12 deficiency, consider taking a supplement as well.

Linda Antinoro, R.D., L.D.N., J.D., C.D.E., is a senior nutritionist at Brigham and Women's Hospital. She is also a certified diabetes educator. Ms. Antinoro counsels patients at the Nutrition Wellness Service.
