Several factors can cause a person to have classic signs of dementia, including a deficiency in vitamin B12. “Vitamin B12 deficiency can cause cognitive impairment, including impairments in thinking,” says Dr. Scott Kaiser, a geriatrician and director of Geriatric Cognitive Health for the Pacific Neuroscience Institute in Santa Monica, CA. “That can definitely mimic signs of dementia.”

Couple that with the fact that older adults are more likely to have trouble fully absorbing vitamin B12, putting them at risk for a deficiency, and doctors say that vitamin B12 deficiency should at least be on the radar of people with older loved ones. Unlike dementia, this is a health issue that can be reversed. 

But what does a vitamin B12 deficiency look like, and how can you tell it apart from dementia? Doctors explain.

What is vitamin B12?

Vitamin B12 is a water-soluble vitamin that’s naturally present in some foods, although it’s also available as a dietary supplement and prescription medicine, according to the National Institutes of Health (NIH). This vitamin helps your body make DNA, and also plays a role in the development and function of the central nervous system, which includes the brain and spinal cord. 

Your body can’t make vitamin B12, so you need to get it from outside sources like meat, dairy, eggs, fortified foods, and b12 supplements, the NIH says. Most adults need 2.4 micrograms of vitamin B12 a day, although the numbers are slightly higher during pregnancy and breastfeeding. 

Causes of vitamin B12 deficiency

There are a few reasons why someone might develop a vitamin B12 deficiency. Following a vegan diet for years is a big one, says Deborah Cohen, D.C.N., an associate professor in the department of clinical and preventive nutrition sciences at Rutgers University School of Health Professions. “Humans can store a small amount of vitamin B12,” which is why it may take a while for a deficiency to show up, she says. 

But Cohen says there are plenty of other risk factors for vitamin B12 deficiency, including taking the diabetes drug metformin and certain medications for gastroesophageal reflux disease (GERD) like proton pump inhibitors for years. “These drugs decrease secretion of intrinsic factor—a protein secreted by cells in the stomach which is vital for the transport of B12 from the stomach to the last part of the small intestine, where it is absorbed,” Cohen explains.

People who have had stomach surgery for weight loss, older adults, and people with gastrointestinal conditions like Crohn’s disease and celiac disease are also at risk for a B12 deficiency, she says. 

Vitamin B12 deficiency symptoms 

Vitamin B12 deficiency has a few hallmark symptoms, according to doctors:

• Lack of energy
• Mental fatigue
• Nausea, vomiting, or diarrhea
• Lack of appetite
• Weight loss
• Yellowish skin

“B12 is essential for energy production,” says Dr. Amit Sachdev, medical director in the Department of Neurology at Michigan State University. “The most common manifestation of B12 deficiency is fatigue.” That fatigue and related symptoms can be confused with symptoms of depression and dementia, he says. 

People with vitamin B12 deficiency may act forgetful and confused, and struggle with concentrating and accomplishing tasks, Kaiser says. In more severe vitamin B12 deficiencies, a person may develop delusions and paranoia. “That could mimic dementia,” Kaiser says. 

How to tell a vitamin B12 deficiency from dementia symptoms

Doctors say it’s hard to tell from a physical exam if a person has a vitamin B12 deficiency or dementia. “There is no way to tell the difference based on [cognitive] symptoms,” says Parul M Goyal, M.D., assistant professor of medicine at Vanderbilt University Medical Center and director of Medicine for Seniors at Vanderbilt One Hundred Oaks. 

However, having gastrointestinal symptoms that started around the same time as cognitive issues may raise a doctor’s suspicion for vitamin B12 deficiency, Sachdev says. “The combination of body and cognitive changes is a major clue that a treatable cause such as B12 deficiency could be the issue,” he says. 

How vitamin B12 deficiency is detected

If a doctor suspects a vitamin B12 deficiency, they will usually order blood work to check a patient’s levels, Kaiser says. But having lower vitamin B12 levels doesn’t automatically mean that someone’s symptoms are being caused by the deficiency. 

“B12 deficiency is also more common in people with Alzheimer’s disease, so you may have two things going on,” Kaiser says. As a result, doctors will usually recommend taking a vitamin B12 supplement and seeing what happens. “If you treat the vitamin B12 deficiency and symptoms improve, that will help you know what is causing them,” Kaiser says. 

But Sachdev says that if your loved one has regular well visits with blood work, things should never get to this point. “Routine lab monitoring for B12 at well checks is the most common way that deficiency is detected,” he says.

What to do if a loved one has dementia-like symptoms

If your loved one is showing signs of dementia, doctors stress that it’s important to see a healthcare provider for an evaluation. “A lot of people will avoid getting an evaluation because of common misconceptions that these memory changes are normal with increasing age, but that’s not a helpful assumption,” Kaiser says. “There is a misconception that there’s nothing we can do about it—that’s not true.”

Once you get an evaluation, a doctor will usually order a blood test to check for a vitamin B12 deficiency, along with other potential factors that could cause dementia-like symptoms, Sachdev says. If your loved one does, in fact, have a vitamin B12 deficiency, they’ll likely be prescribed oral or intramuscular supplements, Sachdev says. If they’re taking a medication that may be behind the deficiency, like a proton pump inhibitor or metformin, a doctor may recommend trying a different type of drug, Goyal says. 

Ultimately, doctors stress that a vitamin B12 deficiency and the symptoms that come with it are reversible. “The effects of supplements are often noticed within weeks,” Sachdev says. 

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