Vitamin deficiencies linked to fatigue, brain fog and breathlessness, doctors warn

Fatigue, brain fog and shortness of breath can be red flags that your body is lacking key vitamins and minerals, doctors say. While tiredness is common and often attributed to stress or aging, a deficiency in vitamin B12, iron or folate may underlie these symptoms. Early identification matters because some deficiencies can cause lasting nerve or cognitive damage if left untreated. A growing body of guidance from health professionals highlights who is most at risk and what steps people can take to confirm and address the problem.

Vitamin B12 is essential for the brain to produce chemicals that carry signals between nerve cells, and for maintaining the protective coating around nerves. A chronic deficiency can manifest as memory problems that may be mistaken for early dementia, and tingling in the hands and feet as nerve function deteriorates. The risk is not uniform across ages. About 15% of people aged 15 to 29, and around 20% of those over 60, have B12 levels that are not frankly deficient but are low enough to cause symptoms. In older adults, reduced stomach acid production can hamper B12 release from food, increasing vulnerability even for those who eat animal products. Some groups are particularly prone to deficiency: vegans, older adults, and people taking proton pump inhibitors to treat acid reflux, which suppress stomach acid and can reduce B12 absorption.

A striking trend cited in recent research is the diminishing B12 content in milk since 1996, a shift tied to changes in cattle feed. Quadram Research Institute’s 2023 review cited that milk now contains roughly half the B12 it did in the mid-1990s, a factor that may contribute to lower intake in the population when dairy is a primary source. Beyond dairy, sources such as beef, salmon and eggs remain important, and fortified plant foods, including some plant milks, can help. For those who avoid animal products, supplementation is often necessary to maintain adequate B12 levels. If age-related absorption issues or long-term acid-suppressing medication are involved, doctors may recommend supplements or injections to ensure adequate B12.

Iron deficiency is another common cause of fatigue, poor concentration and breathlessness. Iron helps make haemoglobin, the protein in red blood cells that ferries oxygen to tissues throughout the body. When oxygen delivery drops, tissues with high energy demands—such as the brain and nerves—are affected first. Folate (vitamin B9) also plays a role in red blood cell production, and a deficiency in any of these nutrients can leave a person exhausted and short of breath during routine tasks.

In the United Kingdom, iron deficiency affects an estimated 3% of men and 8% of women. The shift away from red meat consumption may influence iron intake, since heme iron found in animal products is more readily absorbed than plant-based iron. In men and postmenopausal women, iron deficiency can stem from chronic blood loss from the gut, which can be due to issues such as ulcers; unexplained iron-deficiency anemia should always be investigated by a clinician. Iron deficiency often requires iron supplements, because diet alone typically cannot fully replenish stores, especially when losses are ongoing from heavy periods or gut issues.

Folate deficiency is more common than many realise. Folate is abundant in leafy greens and beans and has declined in several age groups between 2008 and 2019. The latest National Diet and Nutrition Survey data show 12% of teenagers, 4% of adults aged 19 to 64, and 2% of those over 65 are deficient in folate. Folate is crucial for women of child-bearing age because it helps prevent neural tube defects in early pregnancy. A 2023 study in the American Journal of Clinical Nutrition found that 83% of women planning pregnancy had folate levels below the threshold linked with birth defect risk. To address this, the government plans to add folic acid to white flour by the end of 2026, including directly to bread and baked goods. For women planning pregnancy, a daily 400 micrograms of folic acid is advised.

Addressing these deficiencies typically starts with a doctor’s check. If symptoms suggest iron deficiency, a blood test will determine whether the problem lies primarily with iron stores. Iron deficiency is the hardest to fix with diet alone because absorption is tightly regulated by the body. While increasing intake of iron-rich foods such as red meat, beans, tofu and whole grains can help, many people still require supplements. Folate deficiency, by contrast, is usually easier to fix thanks to abundant dietary sources and fortified foods. For those who are vegan or vegetarian, boosting B12 intake through supplements is generally recommended because plant-based sources alone may be insufficient.

The best approach is to talk with a GP if you notice persistent fatigue, trouble concentrating, or shortness of breath. A blood test can assess iron, folate and B12 levels, among other markers. If a deficiency is confirmed, the treatment path depends on the nutrient and the underlying cause. For example, iron supplementation is common when stores are low, particularly when losses are ongoing. B12 supplementation may be required for those who cannot absorb the vitamin effectively from food, including some older adults and those on acid-suppressing medications. In many cases, people report feeling brighter and more energetic within weeks of starting appropriate treatment.

In a reader question about stomach noises and embarrassment in meetings, Dr. Leeming notes that stomach gurgling is normal and usually not a sign of illness. The sounds arise as the gut moves food, fluid and gas along the digestive tract. They can be louder when the stomach is relatively empty or during digestion after a meal. Practical tips include having a small protein- and fiber-rich snack before a meeting and sipping water to dampen the noise. If noises accompany discomfort, bloating or changes in bowel habits, it’s worth discussing with a GP to rule out conditions such as irritable bowel syndrome.

If you think these deficiency symptoms ring true for you, the first step is to consult your GP, who can arrange a blood test to check B12, iron and folate levels and guide appropriate treatment. For vegans and vegetarians, or people with absorption issues, supplementation is often a practical and effective route to replenish stores and protect nerve and cognitive function over time. And because the body’s needs and risks vary with age, lifestyle and medications, individualized medical advice remains essential to ensure safe and effective correction of any deficiency.