The increasing popularity of plant-based diets has a certain number of health benefits. However, plant-based diets can pose a crucial challenge that is too often overlooked. Across the world, infants and young children have varied levels of B12 deficiency, and the incidence is much higher than anticipated, especially in those consuming vegetarian or vegan diets.

Vitamin B12, also known as cobalamin, is critical in developing the brain and nervous system and keeping blood cells and DNA healthy.

Infants born to women consuming a vegan diet have tiny reserves of B12. Additionally, the breast milk of vegan mothers contains small amounts of B12, so when infants of women who consume no animal products are exclusively breastfed, there can be a B12 deficiency so great that it can result in neurological damage, anemia and failure to thrive. B12 deficiency can interfere with normal development, negatively affecting language, learning ability and fine motor skills.

B12 deficiency in young humans can be nonspecific and might not be associated with anemia; however, the deficiency may include one or more symptoms: loss of muscle tone, inability to sit or walk without support, fainting, convulsions, tremors and vision problems. When a B12 deficiency is identified and treated early with B12 supplements or B12 injection, developmental issues can be reversed within a few months. Otherwise, damage to the nervous system and impaired development can be permanent.

Question: Why are vegetarian and plant-based diets more prone to B12 deficiency?

Answer: Vitamin B12 is found naturally only in animal foods: fish, meat, poultry, eggs, milk and other dairy products. Plant foods have essentially no vitamin B12 unless they are fortified. Although an increasing number of websites are promoting foods such as tofu and tempeh as containing B12, the amounts are too insignificant to meet nutrient requirements. Nutritional yeast is sometimes fortified with B12, and plant-based “milks” come in natural and fortified versions. B12 amounts will be listed on the food labels.

Q: Wouldn’t a pregnant woman know if she was B12 deficient?

A: Because it can take many years for symptoms of a B12 deficiency to become apparent, women limiting B12 from their diet may be depleting the reserves necessary for normal fetal development. Even before a woman’s red blood cells display the signs of B12 deficiency, she may start feeling depressed. Besides the folate supplement recommended during pregnancy, a B12 supplement should also be considered.

Besides a plant-based diet, having gastrointestinal issues or a chronic low-iron status can decrease how much B12 is absorbed. If you are considering pregnancy, it might be time to get a B12 checkup.

Joannie Dobbs, Ph.D., C.N.S. and Alan Titchenal, Ph.D., C.N.S. are retired nutrition faculty from the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa.