A man on a 20-year vegan diet was hospitalized after his arm went numb for four days and he experienced troubled speaking.

The peculiar medical case of the 39-year-old man was published in the Cureus Journal of Medical Science. The report noted that the unnamed man had ‘undetectable’ vitamin B12 levels due to his ‘strict’ vegan diet.

Vitamin B12, also called cobalamin, is a naturally occurring nutrient found in meat, eggs, and dairy products. Deficiency due to vitamin B12, which is also available in supplements, can severely damage the nervous system as it is essential for nerves and oxygen-carrying red blood cells. The damage to the nervous system can become irreversible if left untreated for more than six months after symptom onset, according to Insider.

“Although severe vitamin B12 deficiency is rare in the United States, recent increases in the adoption of vegan lifestyles have led to a significant rise in the rates of B12 deficiency,” doctors wrote in the report.

The man sought medical attention when he felt ‘pins and needles’ in his arms along with numbness for four days. He also witnessed problem in speaking and shortness of breath, the doctors added. Other symptoms included intermittently blurry vision, lightheadedness, and lethargy.

Following analysis, it was found that the man had near-zero vitamin B12 levels as well as very low levels of red and white blood cells and platelets.

Those who haven’t consumed eggs, dairy, and meat for more than five years are at risk of vitamin B12 deficiency, according to the British Dietetic Association. The agency further call on long-term vegetarians and vegans to regularly get their vitamin B12 levels checked and supplement their diet with around 10 micrograms per day of vitamin B12.

The man was treated with three blood transfusions and daily vitamin B12 injections for two days. His vitamin B12 injection dosage was gradually reduced with regular injections for five days at home, followed by an injection every week for four weeks, and finally once a month.

The man showed drastic improvement after his treatment began. After just one day of treatment, the man’s word-finding problems improved, and in two days, his coordination, tiredness, and breathlessness ameliorated. After one month of treatment, his confusion was “completely better,” but there was still some numbness in his left hand, the doctors said.

“This case highlights the importance of taking a thorough history, including dietary habits, when hematologic and neurologic symptoms may indicate a vitamin deficiency. It also highlights the importance of vitamin B12 supplementation for patients following a strict vegan or vegetarian diet,” doctors concluded in the report.

Despite this grave medical case, veganism does have an edge over a non-vegetarian diet, according to a separate study.

“Vegan diets have been linked to the reduction of risk for multiple chronic health conditions associated with heart disease, type 2 diabetes, certain types of cancer, and obesity. Due to its potential disease prevention links, it is not surprising that vegans may live longer, as following a vegan diet is linked to reduced occurrence of chronic disease. However, more research is needed to definitively conclude that vegans live longer than non-vegans,” Brooke Jacob, a registered dietitian at ChristianaCare, said.