Thousands might have hidden blood situation that medical doctors miss as a result of exams seem ‘regular’ – it raises danger of most cancers, coronary heart illness and early dying

Hundreds of thousands of Britons may have a hidden blood condition that puts them at greater risk of serious illness and an early death, a major study suggests.

Anaemia – commonly caused by iron deficiency – has long been linked to a number of health problems, including heart failure, pregnancy complications and dementia.

Now researchers from the University of Glasgow say that people with ‘borderline anaemia’ – who may not be identified under current diagnostic guidelines – similarly face an increased risk of cardiovascular disease, cancer and premature death.

The study – published in the journal Annals of Internal Medicine – analysed data from nearly half a million UK Biobank participants over a decade.

It is one of the biggest investigations of its kind into the link between haemoglobin levels, serious disease and early death.

Scientists analysed blood samples collected at UK Biobank centres to measure participants’ haemoglobin levels – the protein in red blood cells that carries oxygen around the body.

They found that extremes at either end – having too much or too little haemoglobin – were associated with the highest risk.

Currently, anaemia is diagnosed using thresholds set by the World Health Organisation (WHO) that have remained unchanged for half a century.

Under current guidelines, anaemia is only diagnosed once the amount of haemoglobin – the protein in red blood cells that carries oxygen around the body – falls below a set level.

But researchers now believe this cut-off may be missing people at risk.

They found that people whose haemoglobin was low, but still considered within the normal range, were more likely to die early than those with higher levels.

Dr Malek Ahmad, clinician-scientist at the University of Glasgow and study lead author, said: ‘Risk already starts to increase with borderline anaemia, before haemoglobin falls below the current WHO threshold.

‘Currently, many doctors do not even recognise a person has anaemia until its moderately severe.

‘Showing that borderline anaemia is associated with increased risk and a high prevalence of iron deficiency should encourage investigation and treatment of a broad range of patients with mild/borderline anaemia.’

Anaemia is most commonly caused by iron deficiency, which leaves the body unable to make enough healthy red blood cells. A lack of vitamin B12 or folate can also be responsible.

Common symptoms include tiredness, pale skin, irritability and a racing heartbeat.

Iron deficiency can be caused by not getting enough iron from food, but heavy periods and pregnancy are also common causes.

Long-term health problems, including kidney disease and conditions that cause inflammation in the body, can also lead to anaemia.

Some medicines can make it harder for the body to absorb iron, including common heartburn drugs such as omeprazole. Calcium and zinc supplements and certain antibiotics can also interfere with iron absorption.

However, the researchers stressed that their findings do not prove that low haemoglobin itself causes people to die earlier.

They now want to investigate whether the guidelines should be updated to take account of factors such as diet, stress and obesity, which could help doctors spot people at risk earlier.

Around two billion people worldwide are thought to have iron deficiency, including 1.2 billion who have developed iron-deficiency anaemia.

In the UK, an estimated three per cent of men and eight per cent of women have the condition, while more than 57,000 people are admitted to hospital with anaemia every year.

In many cases, however, the condition can be treated relatively simply. A daily iron supplement – costing as little as 10p a pill – can be enough to restore iron levels.

Eating more iron-rich foods can also help, including dark leafy vegetables such as kale, fortified breakfast cereals and red meat.

It comes amid growing concern over a rise in the number of Britons being admitted to hospital because they are deficient in essential vitamins and minerals.

Earlier this year, NHS figures revealed a dramatic increase in patients admitted with anaemia caused by iron deficiency, as well as illnesses linked to a lack of B vitamins.

The Royal College of GPs warned that the cost-of-living crisis has made a nutritious diet ‘increasingly unaffordable’ for some people, describing the figures as ‘very concerning.’