A pregnant woman whose legs went numb was diagnosed with vitamin B12 deficiency. Doctors said her diet 'lacked nutrition.'

• A pregnant woman who felt lethargic and had numb legs was diagnosed with a vitamin B12 deficiency.
• The woman ate minimal animal products — a vitamin B12 source — and her diet "lacked nutrition."

A pregnant woman whose legs went numb was diagnosed with a vitamin B12 deficiency because her diet "lacked nutrition," according to a report.

The unnamed woman in her late twenties went to the emergency room after her legs went numb and she experienced symptoms including lethargy and worse-than-usual shortness of breath when she was physically active, OB-GYN doctors wrote in a case report published in BMJ Case Reports on Thursday. These are all symptoms of vitamin B12 deficiency. Others include: irritability, diarrhea, a tender tongue, and a fast heart rate.

Blood tests confirmed that the woman, who was almost 30 weeks pregnant, had a vitamin B12 deficiency.

Pregnant people need more vitamin B12 than others

Vitamin B12 is essential for nerves and the red blood cells that carry oxygen around the body. Deficiency typically has two causes: malabsorption because of conditions like pernicious anemia, or because a person isn't eating enough.

The vitamin is found naturally in meat, eggs, and dairy products. People who don't eat animal products can get vitamin B12 from sources including fortified breakfast cereals, nutritional yeast flakes, and marmite.

Vegans and those who haven't eaten eggs, dairy, and meat for more than five years are at risk of vitamin B12 deficiency, according to the British Dietetic Association, and should get their status checked.

Most people in the US eat enough of the nutrient, National Institutes of Health data suggests, which is 2.4 micrograms every day. For example, three ounces of cooked salmon or pan-fried beef contains the daily vitamin B12 allowance.

However, people need more of it when pregnant — up to 2.6 micrograms. One study from Canada featuring 368 pregnant women found 38% were deficient when they gave birth. A deficiency risks complications including: birth defects, a miscarriage, and low birth weight, according to the BMJ report.

In this case, the woman had two previous miscarriages, but it's unclear if those were linked to her vitamin B12 levels.

The woman's diet 'lacked nutrition'

The doctors said that the woman, who had a BMI of 40, meaning she had severe obesity, "was not a vegetarian, but her diet lacked nutrition."

"The cause of her vitamin B12 deficiency was thought likely to be due to a nutritional deficiency as there was minimal intake of animal products in her diet," they wrote.

People who are obese, have had bariatric surgery, or use medications for underlying health conditions such as metformin for type 2 diabetes, are at increased risk of vitamin B12 deficiency, they said.

Doctors treated the woman with a regimen that included daily vitamin B12 injections for one week, followed by weekly injections for a month.

The woman carried the baby to term, they said.