Suffering from the type of tiredness that leaves you glued to the office Nespresso machine is a daily reality for many of us. With social media, work, responsibilities and dating apps all cloying for our attention, it’s a simple fact of life that human beings are busier than ever.

But sometimes that gnawing urge to crawl under your desk and nap in the fetal position may not solely be down to the fact you stayed up late scrolling skincare tutorials on TikTok. You might be suffering from a B12 deficiency.

B vitamins provide a good chunk of our essential energy, so it stands to reason that if you’re falling short, it could be keeping you stuck in a constant state of zombie-like fatigue. To help you identify the easy-to-miss signs, we’ve rounded up some telltale symptoms of a B12 downer and how you can remedy the problem fast.

1. Tiredness

Vitamin B12 is important for many reasons, but its main role is to facilitate the production of red blood cells, which carry fresh oxygen around the body. If you’re low on B12, your tissues and organs struggle to get the oxygen they need to function optimally, which can result in a tell-tale sluggish feeling – even on days when you’ve banked eight hours of sleep.

In severe cases, B12 deficiency can lead to anaemia, specifically megaloblastic anaemia, where the body produces abnormally large red blood cells that struggle to exit the bone marrow and enter the bloodstream to deliver oxygen.

While fatigue is a common symptom of a B12 deficiency that can be noticeably remedied with supplements or B12 shots, evidence that the vitamin has any additional ‘energy boosting’ benefits for people sitting in a normal range is pretty lacking. This is why it’s always important to get your levels checked out by a doctor, before you start chugging supplements you might not even need.

2. Brain fog

Constantly forgetting your email login and struggling to stay on task? It could be a sign your B12 levels are flagging. As this vitamin provides cofactors that form myelin, a protein that plays a role in forming a protective myelin sheath that cushions your spinal, cranial and peripheral nerves, a lack can cause damage to the nerves resulting in neurological symptoms like brain fog and memory issues.

Compounding this theory, a small 2020 study on 202 patients with minimal cognitive impairment (the in-between stage between typical thinking skills and dementia) found that 84% of those who were deficient in B12 and took a supplement of the vitamin saw an improvement in their cognitive abilities.

3. Mouth ulcers

There’s nothing worse than waking up to a biblical sore on the roof of your mouth, and while they’re often just a fleeting annoyance, recurrent ulcers can be a warning sign to get your vitamin levels checked.

A deficiency in B12 leads to these excruciating oral craters because the vitamin plays a major role in cell production and tissue health. So when levels are low, the mucous membranes in the mouth can become compromised. Case in point: research from Ben-Gurion University of the Negev in Israel found that when the subjects in the study were given a nightly dose of vitamin B12, it had a positive effect on recurring canker sores.

Of course, while there are many reasons you can suffer from ulcers (stress being a big culprit), low vitamin B12 levels often manifest in other oral issues like glossitis (a red tongue), burning sensations and cracking lips, so it’s worth keeping a general eye on the area.

4. Bad moods

Irritation can be caused by many things – traffic jams, slow walkers, poor wi-fi signal – but if you’re constantly feeling low, a B12 deficiency could be just one contributing factor.

B vitamins have long been linked to depression in scientific study, but because mental health can be a complex and multi-faceted issue, scientists don’t fully understand the connection between the two.

One possible theory is the effect of vitamin B-12 on the levels of the feel-good hormone serotonin in your brain, as well as the mood-supporting amino acids homocysteine and methionine. Whatever’s going on in our grey matter, researchers exploring the link in a 2005 study seemed to think it was a worthwhile link, suggesting that people with depression could benefit from taking a 1-milligram supplement of B12 daily.

Who is most at risk of a vitamin B12 deficiency?

Older adults and vegans or vegetarians might want to be particularly diligent about checking their B12 levels, as around 15 percent of adults over age 65 run low, while one small study estimated that 40% of vegans have a deficiency.

NHS GP Dr Anatalia Moore says: “As B12 is found naturally in animal based products, non-meat eaters need to lean on fortified plant-based dairy alternatives and yeast products such as marmite. However, I would always recommend those following a vegan diet take a quality supplement to make sure they’re getting adequate levels.

“As well as plant-based eaters, people who suffer from excess stomach acid and those who take metformin, a common medicine used to help diabetes, are at a higher risk of deficiency. So too are people with bowel conditions that affect the functioning of the small bowl and its ability to absorb.

What should I do if I think I have a vitamin B12 deficiency?

“It’s fairly hard to distinguish a B12 deficiency, as the range of symptoms are very broad, and the impact felt on both our physical and mental health is varied,” says Moore. “If you’re experiencing symptoms, speaking to a doctor will help you to get a diagnosis through a blood test.

“Many of the symptoms of B12 deficiency can be caused by a myriad of other conditions such as iron, vitamin D and folic acid deficiency, depression or stress, diabetes, thyroid concerns and so on. As well as finding out what the cause of your symptoms is, a qualified medical professional can suggest the correct supplementation, medicines or other treatment that can help to resolve your concerns.”