Takeaway
Clinicians should remember to watch for fatigue in patients shifting to plant-based diets; a B12 test can reveal a significant, reversible cause of feeling poorly.
Lifelong Learning in Clinical Excellence | March 10, 2025 | 2 min read
By Selvi Rajagopal, MD, MPH, Johns Hopkins Medicine
I recently saw a 66-year-old woman for an annual physical. She shared that she’d had generalized fatigue over the past few months and couldn’t explain it. She reported no weight changes was sleeping at least eight hours per night. She wanted to start exercising regularly but feeling tired all the time made it difficult.
Given her nonspecific symptoms I decided to take a more thorough history of her lifestyle. I learned she’d focused on a more plant-based diet over the past year. She preferred vegetarian sources of protein and didn’t take any vitamins or supplements. The rest of her review of systems was normal and the exam showed no abnormalities.
I decided to order labs to further evaluate her symptoms, including iron, TSH, vitamin D, and vitamin B12 levels. All labs were normal other than vitamin B12 level, which came back at 130pg/mL (normal is above 300pg/mL). We agreed to add a vitamin B12 supplement to help restore her levels to normal.
In three months, she returned for a follow-up and on repeat testing her vitamin B12 level was normal. She reported a significant improvement in her energy levels and exercise tolerance.
What’s the role of vitamin B12 in the body?
Vitamin B12 plays a role in neurocognitive processes in the body, including nerve signaling and brain function. It also supports DNA formation and red blood cell development.
Where do people typically get vitamin B12 from?
Vitamin B12 typically is found in animal sourced foods and also in fortified foods. These include seafood (clams, trout, salmon, and canned tuna), meat, eggs, liver, and fortified cereals.
What are the signs of B12 deficiency?
B12 deficiency can lead to megaloblastic anemia, with symptoms of weakness and fatigue. B12 deficiency can also lead to peripheral neuropathy, typically symmetric and involving the legs more than the arms, and can also be seen in the fingers and toes. This neuropathy can lead to gait alterations. Individuals may also experience changes in mood (depression, psychosis), cognitive slowing, or memory impairment. These symptoms may be more subtle (like general mood irritability) but depending on the degree of deficiency they can be more severe. Gastrointestinal symptoms of B12 deficiency may include tongue pain, swelling, tenderness, or glossitis.
When should we consider evaluating for B12 deficiency?
1. Anemia
2. Mood or cognitive changes
3. Peripheral neuropathy symptoms
4. Fatigue
5. Gastrointestinal symptoms such as glossitis or tongue soreness
6. Malabsorptive conditions, including diarrhea, gastrectomy/ileal resection, inflammatory bowel disease, chronic use of Metformin, or proton pump inhibitors
7. Inadequate nutritional intake, including vegan diet, alcoholism, older individuals, or those with anorexia
B12 deficiency is often an insidious condition that can be easily overlooked without a thorough evaluation. Careful history taking can help uncover this potentially serious but treatable condition.
This piece expresses the views solely of the author. It does not necessarily represent the views of any organization, including Johns Hopkins Medicine.