How vitamin B12 deficiency may disrupt pregnant women’s bodies

Despite living in an age of dietary abundance, vitamin B12 deficiency is on the rise.

One major culprit? Our growing reliance on ultra-processed foods (UPFs) – those convenient, calorie-dense and nutrient-poor products that dominate supermarket shelves. While they might fill us up, they’re fuelling a global epidemic of “hidden hunger”.

This refers to a lack of essential micronutrients including B12, folate, iron and zinc, even when people consume enough (or too many) calories. It’s often invisible but can have long-term consequences, particularly for vulnerable groups like pregnant women, children and the elderly.

B12 deficiency in pregnancy, especially in the context of a diet high in ultra-processed foods, can disturb how fat is processed and increase systemic inflammation. This raises the risk of long-term health problems for both mother and baby.

A recent study shed light on how B12 deficiency during pregnancy may disrupt two critical systems in the body: fat metabolism and inflammation – both of which are closely linked to chronic diseases like heart disease and type 2 diabetes.

Researchers studied fat tissue from 115 pregnant women with low B12 levels, focusing on two types of abdominal fat: subcutaneous (under the skin) and omental or visceral (around the organs). They also examined lab-grown fat cells exposed to different B12 levels and collected samples from women of different body weights.

The results were striking. Women with low B12 had higher body weight and lower levels of HDL (the “good” form of cholesterol). Their fat cells showed increased fat storage, reduced fat breakdown, and impaired mitochondrial function – the energy engines inside our cells.

Most concerning, these women’s fat tissue released higher levels of inflammatory molecules, suggesting that B12 deficiency might place the body into a constant state of low-grade stress.

Ancient molecule

What sets B12 apart from other vitamins is that it’s made exclusively by bacteria and archaea (tiny single-celled organisms similar to bacteria but with important genetic and biochemical differences). Neither plants, animals nor humans can produce B12.

Some scientists even speculate that B12 may have formed prebiotically, before life itself began. It shares part of its structure, known as a tetrapyrrole ring, with several other of life’s most vital compounds including chlorophyll (for photosynthesis) and heme (for carrying oxygen in our blood).

Although heme has typically been seen as the elder of all these molecules, recent evidence suggests B12 might have come first. Its core structure – a tetrapyrrole known as the corrin ring – has been found in bacteria that don’t produce heme at all, hinting at even deeper evolutionary roots.

Because humans can’t make B12, we depend on our diet to get it. Ruminant animals like cows and sheep are able to host B12-producing bacteria in their stomachs and absorb the nutrient directly. We, however, must obtain it from animal-based foods – or from supplements and fortified products.

Since plants neither produce nor store B12, vegetarians and vegans are at higher risk of this deficiency unless they supplement regularly. As diets become more processed and less diverse, B12 intake and absorption drops, leading to problems in brain function, metabolism and fetal development. Often, the deficiency isn’t spotted until symptoms become serious or irreversible.

The takeaway is that we need to pay more attention to micronutrients, not just calories. Ensuring adequate B12 levels, particularly before and during pregnancy, is crucial. That means prioritising whole foods, fruits, vegetables and quality sources of protein, while limiting ultra-processed products.

From the primordial soup to the modern dinner plate, vitamin B12 is more than a nutrient – it’s a molecular link between our evolutionary past and our future health. Recognising its importance might just be one of the most powerful steps we can take toward a healthier, more informed life.