The Impact of Vitamin B12 Deficiency on Pregnant Women and Fetal Health

Despite living in an era of abundant food supply, vitamin B12 deficiency is increasingly common worldwide. A major contributing factor is the rising consumption of ultra-processed foods—convenient, calorie-dense, yet nutrient-poor products that dominate modern diets. This trend has led to what experts term "hidden hunger," a condition characterized by deficiencies in essential micronutrients such as B12, folate, iron, and zinc, despite adequate or excessive caloric intake.

Vitamin B12, also known as cobalamin, is unique among vitamins because it is produced exclusively by bacteria and archaea—microorganisms that are not present in plants and animals directly. Humans cannot synthesize B12, meaning we depend entirely on dietary sources, primarily animal-based foods like meats, dairy, and eggs, or supplements and fortified foods. Vegetarians and vegans are particularly vulnerable to B12 deficiency due to the absence of these animal products in their diets.

During pregnancy, adequate B12 levels are critical for proper fetal development and maternal health. Deficiency in B12 during this crucial period can disrupt vital bodily systems, especially fat metabolism and inflammatory responses. A recent study examined fat tissue from 115 pregnant women with low B12 levels, focusing on two types of abdominal fat: subcutaneous (beneath the skin) and visceral (around organs). The findings showed that women with B12 deficiency tended to have higher body weight, lower levels of HDL cholesterol—the "good" cholesterol—and increased fat storage in fat cells. These cells also displayed reduced fat breakdown and impaired mitochondrial function, the energy production centers of cells. Moreover, B12-deficient women’s fat tissue released higher levels of inflammatory molecules, indicating a state of chronic low-grade inflammation which can predispose them to conditions like heart disease and diabetes.

B12's biochemical origin is ancient; it is synthesized exclusively by bacteria and archaea, organisms that predate multicellular life. Its structure shares a tetrapyrrole ring with other vital molecules like chlorophyll, responsible for photosynthesis, and heme, essential for oxygen transport. There is some evidence suggesting that B12 might have originated even earlier in Earth's evolutionary timeline, predating heme. Because humans lack the ability to produce B12 internally, we must rely on external sources. Animals like cows and sheep host B12-producing bacteria in their guts, enabling them to acquire the vitamin directly from their diet. In contrast, humans must obtain it through diet or supplements.

Because plants do not synthesize or store B12, vegetarians and vegans are at higher risk of deficiency unless they supplement regularly. As modern diets become more processed and less diverse, B12 deficiency can impair brain function, metabolism, and fetal development, often going unnoticed until symptoms become severe. Ensuring sufficient B12 intake, especially for pregnant women, is vital for both maternal and fetal well-being. This involves prioritizing whole, minimally processed foods, including sufficient amounts of animal products or fortified plant-based options, and limiting reliance on ultra-processed foods.

From the primordial origins of life to our contemporary diets, vitamin B12 serves as a vital molecular link across evolutionary history. Recognizing its importance and maintaining adequate levels through a balanced diet are essential steps toward promoting lifelong health and preventing deficiency-related conditions.