Why sitting down can lead to blood clots

Does your job entail spending most of the day sitting down? If so, you may be putting yourself at greater risk of suffering from blood clots. According to a US study published in the British Medical Journal, women who spent much of their day sitting down, had up to double the risk of suffering from blood clots compared with those who were more active. And the longer spent sitting down, the greater the risk.

These conclusions were reached after analysing an 18 year study between 1990 and 2008, using the Nurses' Health Study cohort of 69,950 female nurses who completed biennial questionnaires. The purpose of the study was to examine the association between sedentary lifestyle and incidents of pulmonary embolism.

Who is at risk of a blood clot?

Those at risk of developing blood clots, particularly deep vein thrombosis (DVT), include long haul flyers or those recovering from surgery. Other categories include family history, aged over 40, overweight, taking oestrogen containing contraceptives, some cancers and pregnancy.

Those fitting within these criteria will often be provided with information regarding their risk and the signs they should look out for. However, such warnings aren’t routinely given out to the population at large. This means all those whose jobs or lifestyles entail long hours sitting down, and who are otherwise healthy, are unlikely to see themselves as being at risk, even though inactivity is known to be a risk factor for blood clots.

Why do blood clots form?

There are many reasons why blood clots form, but they're not always bad news. Blood clots are necessary for preventing open wounds or injuries from excessively bleeding. Once the clot has sealed the injured blood vessel , it gradually breaks down and is reabsorbed.

However, if a blood clot forms in a vein or artery and it doesn't dissolve, a dangerous build-up of blood can occur behind the clot. Spending long periods sitting down decreases the blood flow behind the knees, which can increase the risk of a clot forming. This is why it’s essential to get up and take regular breaks

What is DVT?

Deep vein thrombosis can develop if such a clot forms in a major artery. One way this can happen is through lack of movement and blood circulation becomes abnormally sluggish. If the clot does not break down, part of it may break free and travel through the bloodstream to reach the lungs, leading to a pulmonary embolism. In fact, blood clots such as these are responsible for 60,000 deaths in the United States every year.

How do you know if you have a clot?

Often, you'll have no idea if you have a blood clot. According to the National Heart, Lung and Blood Institute, only around 50 percent of people with DVT display any symptoms. And those that do, may mistakenly attribute early warning signs to something else.

For example, pain or tenderness in the calf area could be put down to a pulled muscle or strain. However, experiencing signs such as swelling, pain or tenderness on the leg, or a feeling of warmth or red or discoloured skin in the leg could indicate early signs of DVT, more so if such signs occur soon after long periods of inactivity.

Although the results from the nurses’ study present worrying news for the less active population, there are certain limitations to the findings. For example, data collected is only based on a study of adult females, so males or younger people may have different outcomes.

However, the findings are significant. And with sedentary lifestyles on the increase, it's more vital than ever that people are made aware of the potential danger of blood clots associated with spending long periods of time sitting down. Just getting up and walking around for five minutes every hour may help prevent unnecessary deaths in the future.