The overlooked reason you’re feeling tired all the time

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One of the commonest medical symptoms that sends people to their doctors is persistent fatigue. People report that they feel “tired all the time” so often that GPs give it the acronym TATT in patient notes.

There are many potential causes , but now, a study has suggested that two possible explanations should be considered more often – deficiencies of two B vitamins, called B12 and folate, also called B9.

For various reasons, including some growing health conditions and the popularity of veganism, it is becoming more common for people to be deficient in these vitamins. So, what are the signs and why are these nutrients so important?

B12 and folate are important substances involved in a large group of metabolic processes, including making DNA – which means they are essential for tissue growth and repair – and making brain signalling chemicals involved in mood and motivation.

If someone is persistently tired, the nutrient deficiency first suspected might be lack of iron. Thanks to NHS awareness campaigns, people may have also heard of type 2 diabetes as a possible cause.

But lack of B vitamins probably won’t jump into most people’s minds, said Dr Dan Baumgardt, an academic GP at the University of Bristol, who wasn’t involved in the study. “These are nutrients the public are less familiar with,” he said.

There are many tests that doctors can do to investigate fatigue. “Practically every single condition in the medical dictionary can cause tiredness in some form,” said Dr Baumgardt. These include pregnancy, depression, carbon monoxide poisoning and chronic fatigue syndrome, also known as myalgic encephalomyelitis.

NHS guidelines body Nice recommends a range of tests and possible diagnoses GPs should consider. Blood tests for B12 and folate levels are on that list, but they are classed as “additional investigations”. In other words, they are not in the first group of tests, points out Dr James Gill, a GP and lecturer at Warwick Medical School.

And there’s a hitch. Blood tests for B12 and folate levels aren’t always correct on whether someone really is deficient, because levels in the blood may not reflect levels in the body’s tissues.

In fact, a different blood test, for a substance called homocysteine, may give a better picture. Homocysteine is involved in the same group of metabolic processes that use B12 and folate, and people who are deficient in the vital nutrients usually have high homocysteine in their blood.

But often, GPs can’t order homocysteine tests – they have to be requested by hospital doctors, which means they happen less often.

Men and women show symptoms differently

The latest study has highlighted these complexities. Researchers in Japan gave over 600 people questionnaires on their physical fatigue and what might be called mental fatigue, how motivated they felt about doing activities.

They also measured blood levels of vitamin B12, folate, and homocysteine. The results have been published in the journal, Nutrients.

The study showed that higher levels of homocysteine (indicating B12 or folate deficiency) was linked with worse fatigue in men and weaker mental motivation in women.

But blood tests for B12 and folate showed only small correlations with fatigue and motivation, supporting the idea they can be inaccurate. “We recommend measuring homocysteine concentrations,” said Professor Hiroaki Kanouchi, at Osaka Metropolitan University, who led the research.

The study does not prove the vitamin deficiencies were causing fatigue in these people, but does support the need for a trial of supplementation for persistent tiredness, he said.

Dr Gill said that if GPs suspect B vitamin deficiency even when blood tests are normal or borderline, they could still recommend treatment.

Both vitamins can be taken as tablets, and an injection of B12 can also be given for a quick boost. “If a patient is very close to the border, let’s just give you some more,” he said.

Mixed up with signs of ageing

Other signs of B12 deficiency include mouth ulcers, pins and needles in the feet and memory problems or “brain fog”.

“When people start to have reduced levels of B12, it’s a very slow process,” said Professor Martin Warren, a micronutrient researcher at the Quadram Institute. “Gradually, your energy levels drop, you become slightly more tired, you get a little bit of brain fog, all of these things creep up and you might think it’s the ageing process.”

If someone suspects their B vitamin levels are at risk of being too low, they can tackle this with their diet.

Good sources of B12 are all forms of meat, as well as foods that have been fortified with it, like some breakfast cereals and Marmite. Good sources of folate include beans, other pulses and green leafy vegetables.

People who are at high risk of these deficiencies include vegans, as well as people with Crohn’s disease – which reduces nutrient absorption – those taking a diabetes medicine called metformin and drugs to reduce stomach acid called proton pump inhibitors.

“Some people soldier on but anybody who is feeling persistent tiredness should go and see their GP,” said Dr Baumgardt. “If it’s a medical problem we might determine the cause.”

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