People with low levels of iron in the blood have a higher risk of dangerous blood clots, which can cause pain and swelling, but can be fatal if the clot is dislodged and travels into the blood vessels of the lungs.

Scientists at Imperial College London (UK) analyzed blood from 609 patients reviewed at the hereditary hemorrhagic telangiectasia (HHT) clinic at Hammersmith Hospital (London, UK) from 1999 to 2011, to look for differences between the patients who had blood clots and those who did not. HHT is an inherited disease of the blood vessels, the main symptoms of which are excessive bleeding from the nose and gut. Many of the patients had low iron levels because of iron lost through bleeding. The scientists found that low levels of iron in the blood were a strong risk factor for blood clots. Patients who took iron supplements did not have higher risk, suggesting that treatment for iron deficiency can prevent blood clots.

The link between iron levels and blood clots appears to be dependent on coagulation factor VIII, a blood protein that promotes normal clotting. 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. 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, and that this might be the mechanism for the link.

Claire Shovlin, PhD, lead author of the study, said, "Most of our patients who had blood clots did not have any of the known risk factors. We thought that studying people with HHT might tell us something important about the wider population. 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.” In this population, low serum iron levels attributed to inadequate replacement of hemorrhagic iron losses are associated with elevated plasma levels of coagulation factor VIII and venous thromboembolic risk. The study was published on December 14, 2011 in the journal Thorax.

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Imperial College London
Hammersmith Hospital