How many times have you brushed off fatigue and poor concentration as stress, ageing or simply lack of sleep? Most people do it without a second thought. People adjust routines, drink more coffee, promise
an earlier night. What rarely enters the conversation is that these subtle but persistent symptoms may point to something physiological rather than situational.
Vitamin B12 deficiency rarely presents like a clear-cut illness. Its symptoms mirror the strain and pace of modern life, which is why it often slips under the radar until the consequences are far more difficult to reverse.
The scale of the problem is larger than many assume. According to 2025 data from the Indian Council of Medical Research’s National Centre for Disease Informatics and Research (NCDIR), drawn from 20 Indian studies involving nearly 19,000 participants, inadequate vitamin B12 levels were estimated in 51% of the population. Rates were particularly elevated among vegetarians, pregnant women and rural communities. In a separate multicentric review of more than 15,000 asymptomatic adults in northern India, outright deficiency stood at 24.2%.
Globally, the pattern varies by age and diet. Estimates suggest deficiency affects roughly 6% of adults under 60 in higher-income countries, rising towards 20% in those over 60. What remains consistent across regions is the body’s ability to store several years’ supply of B12 in the liver. That reserve can mask depletion for a long time, allowing neurological or blood-related effects to surface only after levels have been low for months or even years.
What Does Vitamin B12 Do in the Body?
“Vitamin B12 is a water-soluble vitamin. It plays a major role in nerve regulation, brain function, DNA synthesis and red blood cell production. Because the body cannot produce it, adequate intake and proper absorption are critical,” explains Reena Poptani, Clinical Dietitian.
In simple terms, B12 underpins some of the body’s most fundamental processes. It supports the insulation of nerves, helps maintain cognitive clarity and ensures that red blood cells are formed properly. Adults require about 2.4 micrograms daily, a modest amount with outsized importance.
“The most common of symptoms of Vitamin B12 deficiency are weakness, fatigue and tingling sensation in feet and hands, irritability, brain fog, memory retention problems, lack of focus, or sore tongue or mouth ulcers,” Poptani adds.
These are symptoms that do not immediately raise alarms. They accumulate gradually. A sense of heaviness in the limbs. Subtle lapses in memory. A tingling that comes and goes. Because they are nonspecific, they are often rationalised away.
“If symptoms like tingling, fatigue, or memory issues persist, a simple blood test can confirm levels and help start treatment early,” she says.
Treatment timelines reinforce the importance of early action. Energy levels may improve within weeks. Blood parameters often reflect change within one to three months. Nerve-related symptoms, however, can take several months to recover. In prolonged deficiency, some neurological damage may not fully reverse, making early detection critical.
Why Are the Early Symptoms of B12 Deficiency?
The overlap between deficiency symptoms and modern living is precisely what makes B12 so elusive.
“The most common of symptoms of Vitamin B12 deficiency are weakness, fatigue and tingling sensation in feet and hands, irritability, brain fog, memory retention problems, lack of focus, or sore tongue or mouth ulcers,” Poptani reiterates.
For younger adults in particular, these signs are rarely linked immediately to a nutrient gap.
“In younger patients, early signs of vitamin B12 deficiency are often subtle and easily attributed to stress or lifestyle factors,” says Dr. Sumit Aggarwal, Director & Head, Internal Medicine, Sarvodaya Hospital, Sector-8, Faridabad.
“Symptoms such as persistent fatigue, mild memory lapses, irritability, mood changes, tingling or numbness in hands and feet, and reduced concentration are commonly overlooked. Some patients may also experience recurrent mouth ulcers or glossitis. Because these symptoms are nonspecific, they are frequently dismissed until neurological manifestations become more pronounced.”
In effect, the deficiency hides in plain sight. A demanding job, exam pressure, parenting stress, hormonal fluctuations, digital overload. Each offers a plausible explanation. The nutritional root may not be considered until symptoms intensify.
Why Is Vitamin B12 Deficiency Difficult to Detect?
Even when individuals undergo routine health check-ups, B12 deficiency can remain undiagnosed.
“Vitamin B12 deficiency is frequently diagnosed late because routine health check-ups may not include specific B12 testing unless anemia is suspected,” Dr. Aggarwal notes. “Moreover, early deficiency does not always present with obvious anemia. Many symptoms—like fatigue, weakness, or mild neuropathy—are mistaken for lifestyle-related issues. The body’s significant B12 storage capacity can also delay overt clinical signs, allowing the deficiency to progress silently over months or even years.”
There is also a diagnostic nuance. “Standard serum vitamin B12 levels provide a useful baseline but may not always detect functional deficiency,” cautions Dr. Aggarwal.
“Some patients can have ‘borderline’ or even normal serum B12 levels yet still exhibit deficiency at the cellular level. In such cases, additional markers such as methylmalonic acid (MMA) and homocysteine levels offer better insight, as they tend to rise when B12-dependent metabolic pathways are impaired. Therefore, clinical correlation alongside laboratory findings is essential for accurate diagnosis.”
In other words, a normal-looking report does not always close the case. Clinical judgement, symptom correlation and, in certain cases, deeper biochemical testing matter. Adults require around 2.4 micrograms daily but intake alone is not the only issue, absorption is equally important.
Can Prolonged Sadness And Depression Be A Sign of B12 Deficiency?
Vitamin B12 does more than support nerve health and red blood cell production. It also plays a role in the creation of brain chemicals that influence mood and cognitive function. Low levels of B12, along with other B vitamins and folate, have been linked to depression. The relationship is complex, but the biological pathway is clear: without adequate B12, certain neurological processes tied to emotional regulation may be affected.
Deficiency can develop due to an imbalanced diet or problems with absorption. Older adults, vegetarians and individuals with digestive disorders such as coeliac disease or Crohn’s disease are particularly vulnerable. In some cases, the cause of low B12 levels remains unclear, which is why clinicians may recommend blood testing when symptoms such as persistent low mood accompany fatigue or cognitive changes.
Supplementation can correct a deficiency, but research findings are mixed on whether vitamin B12 supplements alone reduce the risk of depression or significantly ease its symptoms. High doses may also interact with certain medications, making medical guidance essential. While maintaining adequate B12 through diet or supplementation supports overall neurological health, it does not replace established treatments for depression, including medication and psychological therapy.
Who Is Most at Risk?
Poptani outlines key risk factors:
- Diets low in animal foods
- Vegetarian or vegan diets without fortified plant-based options
- Highly processed, low-nutrient diets
- Very low-calorie or restrictive eating patterns
- Low-protein diets, especially in older adults or those with reduced appetite
- Excess alcohol consumption
- Long-term use of acid-reducing medicines or metformin
- Conditions affecting the stomach or small intestine such as chronic gastritis, Celiac disease, Crohn’s disease, intestinal surgery or bariatric procedures
- Decreased stomach acid
- Reduced production of intrinsic factor, a protein required for absorption in the small intestine
Dr. Aggarwal adds that screening should not be limited to symptomatic individuals.
“Screening should be considered in individuals with risk factors, even if asymptomatic,” he advises. “This includes strict vegetarians or vegans, elderly individuals, patients with gastrointestinal disorders (such as malabsorption syndromes), those on long-term proton pump inhibitors or metformin therapy, and individuals with a family history of pernicious anemia. Women planning pregnancy and patients with unexplained neurological symptoms should also be evaluated proactively to prevent long-term complications.”
What Are The Best Sources of Vitamin B12?
Vitamin B12 is naturally present in animal-derived foods. Sources include:
- Fish, meat, eggs and dairy
- Salmon and tuna
- Organ meats such as liver and kidney
- Milk, cheese and yoghurt
- Fortified cereals or plant milks for vegetarians
For those with mild deficiency, dietary modification may suffice. Most cases respond well to oral supplements. In instances where levels are severely low or absorption is impaired, injections may be required.
The paradox remains striking- Vitamin B12 deficiency is common and is measurable, treatable yet it continues to evade early detection because it looks so much like ordinary life.
The next time fatigue lingers or concentration falters, the explanation may not lie in busyness alone. Sometimes, the body is asking for something far smaller, and far more essential, than we imagine.
