Thrombosis is a medical term that refers to blood clots that form within a blood vessel, restricting the flow of blood through the vessel. Blood clots can develop in veins, arteries, and heart chambers.

The consequences of thrombosis are often severe, including everything from heart attacks and pulmonary embolisms to severe organ damage and even death. Because of this, understanding why thrombosis occurs and identifying the factors that increase the risk of developing blood clots is crucial. One such factor is the season – and some seasons pose a higher risk than others.

Understanding the risk of thrombosis

There are several risk factors for thrombosis. Some of the most common include:.

Obesity
Sedentary lifestyle
Smoking
Pregnancy
Family history of blood clots
Recent surgery or illness

While these factors can make it more likely for an individual to develop thrombosis, they’re not the only factors to consider. Others, such as existing health conditions, can also play a significant role.

With that said, many experts have noticed an interesting trend when it comes to the seasons – and it turns out that certain times of year might increase the risk of developing thrombosis.

Winter: A high-risk season

Perhaps unsurprisingly, the winter months seem to be the time of year when the risk of thrombosis is highest. Several studies have highlighted this correlation – including research published in The Journal of Vascular Surgery.

The authors of the study found that the incidence of deep vein thrombosis (DVT) was significantly higher in the winter months than at any other time of year. This was despite the fact that the incidence of other cardiovascular events such as heart attacks and strokes remained relatively stable year-round.

So why is the risk of thrombosis higher during winter? There may be a few different factors at play here.

For starters, the colder temperatures of the winter months can lead to vasoconstriction – a narrowing of the blood vessels that can reduce blood flow. This can make it more likely for blood clots to form. Additionally, many people are more sedentary during the winter months – whether because of the cold weather, the holidays, or other factors.

This decreased activity can also increase the risk of blood clots forming.

Spring may also increase the risk

While winter is the season most commonly associated with the risk of thrombosis, it’s worth noting that spring doesn’t necessarily offer a reprieve.

In fact, some studies have suggested that the risk of developing blood clots may actually be highest in the spring. A study published in the Journal of Thrombosis and Haemostasis, for example, found that the incidence of DVT was highest during the months of March and April.

What might be behind this association? There are a few possibilities. For one, it’s worth noting that allergy season is in full swing during the spring months.

Some researchers have suggested that seasonal allergies could be a risk factor for blood clots – potentially due to the inflammation and immune response that allergies can trigger. Additionally, there may be more travel occurring during the spring months – whether for spring break or other reasons. As we’ll discuss more below, travel (particularly air travel) can increase the risk of thrombosis.

Summer and Fall: Lower risk?

While winter and spring seem to correspond with a higher risk of thrombosis, that doesn’t necessarily mean that summer and fall are devoid of risk entirely.

However, existing research suggests that the risk of blood clots may be slightly lower during these seasons.

One 2019 study published in the Journal of Thrombosis and Haemostasis found that the risk of DVT was significantly lower in the summer months than in the winter months.

Similarly, a study published in The Journal of Vascular Surgery found that the incidence of DVT was highest in the winter months and lowest during the summer months. Fall falls somewhere in the middle – with some studies suggesting a slight increase in the risk of blood clots compared to summer, but still lower than winter or spring.

Other factors that play a role

It’s important to keep in mind that while seasonal changes can impact the risk of thrombosis, they are by no means the only factor to consider. Other factors that can increase the risk of developing blood clots include:.

Travel, particularly long-distance air travel
Certain medications, such as birth control pills or hormone replacement therapy
Some surgeries, particularly those that involve the lower extremities
Cancer or other health conditions that affect blood clotting
Chronic illness or immobility

As you can see, there are many different factors to consider when it comes to thrombosis risk. However, if you’re concerned about your risk of developing a blood clot, there are steps you can take to reduce your risk.

These might include managing existing health conditions, engaging in regular physical activity, staying hydrated, and talking to your doctor about any medications or other factors that could increase your risk of developing thrombosis.

The bottom line

Thrombosis is a serious medical condition that can be caused by a variety of factors. One of these factors is the season – with winter and spring correlating with higher risk.

Whether you live in a region that experiences significant seasonal changes or not, it’s important to stay vigilant when it comes to your thrombosis risk. By taking steps to manage your risk factor and working closely with your healthcare provider, you can reduce your chances of developing a blood clot and ensure that you stay as healthy as possible in all seasons.