A new study published in the journal Lancet suggests that blood clots in a person’s vein put him at nearly twice the risk of heart attack or stroke within a year. The study confirms the existing belief that all three conditions are linked.

Vein blood clots are often the result of restricted blood circulation in a deep vein, most often in a leg. Known as deep vein thrombosis, the condition is not fatal but can prove to be so if the clots dislodge and pass through the veins to reach the lungs, where they can cause a pulmonary embolism.When blood clots related to heart attacks and strokes are talked about, they are generally the ones occurring in the coronary arteries; blood clots in the veins were not believed to have any serious impact on cardiovascular events. However, there has been growing evidence that this might not actually be the case.

The new study by Dr. Henrik Sorensen and team at Denmark’s Aarhus Hospital provides evidence to suggest the same. The team collated data from Denmark’s medical databases spanning a period of 20 years. Data for more than 25,000 patients with deep vein thrombosis was analysed to measure their risk of heart attack and stroke; patients with heart disease were however, excluded from the study.

The researchers found that the vein condition increased the risk of patients suffering a heart attack or a stroke by as much as 90% within a year compared to people without clots. Their relative risk compared to people without blood clots in the veins continued to remain from 20% to 40% higher over the 20 year period.

“We have shown the link between the diseases for the first time in a very large study,” said Dr. Sorensen. “The diseases had been regarded as totally different.” While the researchers are not sure why vein clots, heart attacks and strokes are linked, they believe obesity might be a major factor.

The Danish team was also surprised by the findings as deep vein thrombosis is a condition vastly different from what is known to be the chief cause of heart attacks. So far, the belief has been that hardening of artery walls is the main reason behind heart attacks and strokes. Veins have not been known to harden due to blood clots.

“The veins don’t have the same process,” Dr. Sorensen said. “Therefore it is surprising there is a link.” According to Dr. Gordon Lowe, a researcher at Glasgow University, this new link between the three conditions could help reduce the number of heart attacks and strokes by increasing the number of people being treated for blood clots.

Dr. Lowe also finds the study to be important on account of it being the first large scale study to look at blood clots in veins. “Such studies have reported conflicting results, partly because of small event numbers and hence limited statistical power,” he said in a commentary in the Lancet.