Vitamin B12 deficiency can leave people feeling shattered with a string of other symptoms. From brain fog and poor concentration to irritability and pins and needles, a lack of the key vitamin can lead to them all.

But what happens if you take a B12 test and it comes back normal yet you still have the symptoms. Expert, Apollo Delhi surgeon Dr Anshuman Kaushal, says there could be an easy answer, yet it is one which is often missed.

Speaking on an Instagram video he says the problem could be a sign of functional B12 deficiency. This is where the body has enough B12 circulating in the blood but its cells cannot use it effectively.

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Most routine tests only look at the total B12 figure and do not measure its active form leaving people to continue suffering the health symptoms. Yet failure to correctly diagnose the issue can lead to permanent nerve and brain problems.

Dr Kaushal, going by the name theangry_doctorsaid: "Normal B12 but still exhausted? You’re not crazy, your cells are starving."

He explained how many patients whose B12 results have been recorded as "normal" still feel a range of symptoms. These include extreme tiredness, feeling depressed and being forgetful along with other nerve issues such as tingling in the hands.

The doctor added: "Congratulations, you've just diagnosed functional B12 deficiency, the award winning illusionist of modern medicine.

"Why should your nerves feel fine when your lab reports can gaslight you instead."

The doctor said most labs only look at serum B12 and don't look deeper to see how the B12 is working in your body. A significant amount of B12 that is circulating in your body is bound to an inactive carrier protein, which means it cannot enter cells or support other bodily functions.

He said while you could get perfect B12 results on paper inside it was "total bankruptcy". He explained: "It's like having money in your own bank account but no atm card. Looks rich, feels broke."

For those who do continue to have these symptoms, the doctor says they should request a test to show how much of the B12 is active. And if these come back as too low, then a patient might need B12 injections to boost their levels.

Vitamin B12 is a key vitamin that helps keep blood and nerve cells healthy. The Mayo clinic explains: "Vitamin B-12 is a vitamin the body uses to make and support healthy nerve cells. It's also used to make healthy red blood cells and the genetic material inside cells called DNA. Vitamin B-12 also is called cobalamin."

The recommended daily amount of vitamin B-12 for adults is 2.4 micrograms (mcg). Older adults may need to eat more vitamin B-12. The ability to absorb vitamin B-12 lowers as a person gets older. Older adults may need to eat 10 to 12 mcg of vitamin B-12 to get enough of this vitamin.

It adds: "Most people get enough vitamin B-12 from a balanced diet. But older adults and people who follow vegetarian or vegan diets may find it helpful to take vitamin B-12 supplements. People who have conditions that keep them from absorbing nutrients, such as celiac disease or Crohn's disease, also may find that vitamin B-12 supplements are helpful."

Vitamin B12 can cause a wide range of symptoms, according to the NHS. These usually develop gradually, but can worsen if the condition goes untreated. Symptoms of vitamin B12 deficiency include:

• rapid breathing or shortness of breath


• headaches


• indigestion


• loss of appetite


• palpitations


• problems with your vision


• feeling weak or tired


• diarrhoea


• a sore or red tongue, sometimes with mouth ulcers


• problems with memory, understanding and judgment (cognitive changes)

Some of these symptoms can also happen in people who have a vitamin B12 or folate deficiency but have not developed anaemia.

Vitamin B12 deficiency can also cause symptoms that affect your brain and nervous system (neurological symptoms), including:

• numbness


• muscle weakness


• psychological problems, which can range from mild depression or anxiety, to confusion and dementia


• problems with balance and coordination


• pins and needles


• incontinence

Dr Kaushal said functional B12 levels can be found through tests which measure levels of methylmalonic acid (MMA) and homocysteine in the blood. He said: "Your B12 levels might look ‘normal’ on paper… but your cells may still be starving.

"Brain fog, fatigue, tingling, low mood — all red flags you shouldn’t ignore. Check your homocysteine & methylmalonic acid — not just serum B12."