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Q: I'm tired often and heard that vitamin B12 can help with fatigue and boost energy levels. Should I be taking a supplement?
A: There's no proven benefit to taking vitamin B12 for fatigue unless you have a deficiency that causes anemia. Start by asking your doctor for a simple set of blood tests for vitamin B12 and related biomarkers. Adults above age 65 and vegans are particularly at risk of a deficiency.
• If you're deficient in the vitamin, you should take a supplement.
For everyone else looking for an energy boost, my advice as a rule of thumb in medicine is, where possible, less is more. Don't take a supplement without a proven benefit. Instead, talk to your physician about other ways to help with energy levels, including making lifestyle changes or getting tested to rule out potential medical issues such as thyroid disease.
• What is vitamin B12 good for?
Vitamin B12 is an essential vitamin that serves several important biological functions, including in metabolism and producing healthy blood cells. Here are the areas where we know supplementation can be beneficial: • Fatigue caused by anemia. People often think of anemia caused by iron deficiency, but low B12 can classically lead to an anemia where the blood cells become abnormally large.
• Certain neurological symptoms, such as trouble walking, numbness or psychiatric issues, because of a deficiency.
Other areas that many people look to B12 as a tonic - including muscle aches, arthritis, insomnia or generalized weakness (in the absence of anemia) - have little to no evidence behind them.
• How do I know if my B12 is low?
The most frequent symptom of low B12 is a vague one: exhaustion. Cognitive changes, irritability and even paranoia have also been linked to cases of vitamin B12 deficiency. So has tongue swelling.
Certain groups are at higher risk of being deficient and should talk to their doctor about getting screened: • Older adults. Around 15 percent of Americans over age 65 have a deficiency related to reduced acid in the aging stomach, which makes it harder to absorb the vitamin B12 that's naturally present in foods. Elderly people are generally able to absorb oral supplemental B12 or vitamin B12 in fortified foods without the same issue.
• Vegans or vegetarians. In one small study, 40 percent of vegans were found to be vitamin B12 deficient.
• Pernicious anemia or other autoimmune conditions. In pernicious anemia, the body produces antibodies that interfere with vitamin B12 absorption. These patients should take lifelong vitamin B12 therapy. Vitamin B12 deficiency is also more common among those with other autoimmune conditions such as vitiligo or thyroiditis.
• Gastrointestinal surgery. People with a history of gastric bypass or other surgeries or diseases (like celiac or Crohn's) that affect particular areas of the intestine can be at higher risk.
• People on certain long-term medications such as metformin and acid-reducing medications. These are known to reduce absorption of B12.
• How can I increase my B12 naturally?
Vitamin B12 is naturally present in animal-based proteins, including meat, fish, eggs and dairy. (Fun fact: It's especially high in clams or beef liver.)
If you're on a fully plant-based diet, you might still get an adequate amount of vitamin B12 from fortified foods, although not always. Some cereals and many brands of nondairy milk, for example Oatly or Silk soy milk, are fortified with B12. Nutritional yeast, a seasoning used in vegan recipes for its cheesy flavor, often is too.
The recommended intake for vitamin B12 in adults is 2.4 mcg. Here's how much vitamin B12 is found in some common foods:
• Salmon, 3 ounces: 2.7 mcg • Nonfat, plain Greek yogurt, 3.5 ounces: 0.7 mcg • 1 large egg: 0.5 mcg • Chicken breast, 3.5 ounces: 0.3 mcg
• What's the best way to absorb vitamin B12?
Some people prefer a vitamin B12 shot, which is typically given in the arm intramuscularly often at your health-care provider's office or pharmacy. If you have a severe deficiency, doctors may recommend starting with the shot, but in general, high-dose oral vitamin B12 replenishes your system just as well as the shots.
• Is there any harm in taking vitamin B12?
Many of my patients wonder what's the harm in just taking a supplement and seeing what happens. Even high doses - over-the-counter pills typically contain 1,000 mcg - are generally considered safe, because our bodies absorb only a fraction of that. But a study published in 2020 in JAMA Network Open found that higher levels of vitamin B12 in the blood were associated with increased risk of death from all causes. Other studies have found a link between high levels of the vitamin and cardiovascular disease and increased risk of hip fracture.
• What I want my patients to know
Unlike many supplements, vitamin B12 is an interesting case where unnecessary consumption is being driven by the patient as well as the prescriber. A 2019 study published in JAMA Internal Medicine found that the majority of vitamin B12 shots are prescribed inappropriately - that is, to people without any evidence of deficiency. Why is this happening? There's probably some component of pressure to respond to patient requests given B12's rise in popularity. All of us could benefit from familiarizing ourselves better with the research.
Previously:
• Why we crave sweets after eating --- and what to do about it
Trisha S. Pasricha is a physician at Massachusetts General Hospital, an instructor in medicine at Harvard Medical School and a medical journalist.
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