New research shows that people who have low levels of iron in their blood have a higher risk of dangerous blood clots that can be fatal.

Scientists at Imperial College London suggest that treating iron deficiency might be important for preventing potentially lethal blood clots in patients with an inherited blood vessel disease.

The researchers said that each year, one in every 1,000 people in the UK is affected by deep vein thrombosis, blood clots that form in the veins, causing pain and swelling and can be fatal if the clot is dislodged and travels into the blood vessels of the lungs.

Trying to find new risk factors for blood clots, researchers studied patients with hereditary haemorrhagic telangiectasia (HHT), an inherited disease of the blood vessels, causing excessive bleeding from the nose and gut, as previous research found that HHT patients had a higher risk of blood clots but were unsure as to why.

"Most of our patients who had blood clots did not have any of the known risk factors ," said the paper's lead author Dr Claire Shovlin, from the National Heart and Lung Institute at Imperial College London and an honorary consultant at Imperial College Healthcare NHS Trust.

"We thought that studying people with HHT might tell us something important about the wider population," she said in the Journal Thorax on Wednesday.

The study consisted of an analysis of 609 patients reviewed at the HHT clinic at Hammersmith Hospital from 1999 to 2011.

The researchers looked at differences between patients who had blood clots and patients who did not have blood clots.

The authors said that many of these patients had low iron levels because of iron lost through bleeding.

The researchers found that low levels of iron in the blood were a strong risk factor for blood clots and patients who took iron supplements did not have higher risk.

The researchers suggested that iron deficiency can prevent blood clots.

"Our study shows that in people with HHT, low levels of iron in the blood is a potentially treatable risk factor for blood clots," Dr Shovlin said.

"There are small studies in the general population which would support these findings, but more studies are needed to confirm this. If the finding does apply to the general population, it would have important implications in almost every area of medicine."

Iron deficiency anaemia is thought to affect at least 1 billion people worldwide, wrote the authors.

The authors explained that the “link between iron levels and blood clots appears to be dependent on factor VIII, a blood protein which promotes normal clotting,” because “high levels of factor VIII in the blood are also a strong risk factor for blood clots, and low iron levels were strongly associated with higher levels of factor VIII.”

They say that this might be the mechanism for the link because the gene encoding factor VIII has sites where iron binding proteins can bind, making it plausible that iron levels could regulate the factor VIII gene.

"We can speculate that in evolutionary terms, it might be advantageous to promote blood clotting when your blood is low in iron, in order to prevent further blood loss," Dr Shovlin said.