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As if cholesterol wasn't enough of a headache for men over 40, another — albeit less common — silent killer lurks inside the veins. Blood clots, which block major blood vessels, can be quite painful and, in rare cases, even cause death. Be aware of their dangers and protect yourself.

What are blood clots?

Normally, when you cut yourself, your blood coagulates and seals the wound, forming a scab to protect it from infection. However, sometimes this essential blood clotting mechanism works against the body. In some cases, blood curdles into a clump (thrombus) that stays lodged in the veins, a condition known as deep vein thrombosis (DVT). Not only can this blood clot restrict blood flow, but it can also travel to narrower and more vital parts of the body, such as the heart, lungs or brain. This can be dangerous and, in rare cases, lead to death.

Where do they occur?

The most common blood clots happen in deep veins, usually in the lower legs, but they can also block vessels in the arms and pelvis. Rarely, and more commonly in dehydrated infants, blood clots can damage the kidney veins.

What are the symptoms?

A blood clot can partially or completely block the blood flow in a vein. In either case, an inflammation develops. Symptoms can include swelling, redness, gradual increase in pain, sharp pain when bending the affected extremity, leg cramps, warmness of the skin near the clot, and discoloration.

Sometimes blood clots produce no symptoms. In fact, up to half of men who have blood clots experience nothing.

What are the causes?

Many factors contribute to the formation of blood clots, ranging from physical inactivity to genetics. The most common causes and risk factors are:

— Prolonged inactivity, like sitting in an airplane or lying in bed for a prolonged period of time due to illness

— Recent surgery, especially orthopedic or heart surgery

— Recent trauma to the body, like leg or hip fractures

— Obesity

— Heart attack

— Cancer

— Genetically acquired blood-clotting disorders

— Damage to blood vessels and changes in normal blood flow

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Who is most at risk?

As the symptoms indicate, men over 40 with sedentary lifestyles or who travel a lot are the most frequent victims. Overweight men and men who have a history of heart disease or cancer are also at high risk.

About 2 people in 1,000 develop deep vein thrombosis, regardless of gender. However, men have a much higher chance of getting recurring clots than women. In a study conducted by the Medical University of Vienna, 20% of men who had a blood clot developed a second one; the risk of a second episode was more than triple for men than it was for women.

How are blood clots detected?

If you have any of the symptoms outlined above, seek medical attention. To detect a blood clot, any of the following imaging tests can be used.

Venography: This is the most accurate test for DVT, but it has some drawbacks, including an increased risk of blood clot formation. A dye is injected into the veins, making them easier to see while highlighting blocked areas.

Ultrasound: The most effective diagnostic method after venography, this procedure forms images out of sound waves that are blasted into your body.

MRIs and CAT scans: While less commonly used, magnetic resonance imaging (MRI) — radio waves used to create images of the organs — and CAT scans — X-rays of different sections of the body — can also be used for diagnosing DVTs.

How can you treat them?

Blood clots can't be eliminated with medication, but anticoagulants (blood-thinning drugs) stop them from growing bigger and prevent new ones from forming; the body eventually eliminates them on its own. A side effect of such drugs is that cuts bleed more and take longer to heal.

It can take several weeks for the body to break up the clot. Affected limbs should remain elevated, in constant motion, and treated with heat if there is pain. Doctors may also prescribe compression stockings, which are tighter at the ankle than the thighs, to help relieve pain.

If a clot is big and poses a threat, a doctor might choose to administer a powerful clot-busting drug. However, these carry a high risk of bleeding, so they are only used in extreme cases.

Can blood clots kill you?

The chances of a clot being life-threatening, especially if it develops below the knee, is practically nil. But if it's above the knee, it can dislodge from the vein and clog a major vessel in the heart, lungs or brain. This is called an embolism and, in rare cases, it can cause a stroke or a heart attack. Usually, the worst complication of blood clots is tissue damage.

How can you prevent them?

The best way to keep your veins clear is to maintain a healthy, active lifestyle. If you travel by plane frequently or have a job that requires you to sit all day, move your legs, change positions in your seat, and get up often to avoid the formation of blood clots. Also, maintain your weight at a healthy level, wear loose-fitting clothes and stay hydrated by drinking lots of water.

Keep an even flow

Your blood feeds your muscles, doles out oxygen to your body and keeps you warm. A blood clot blocks this smooth system and exposes you to serious harm. By taking a few preventive measures, you can avoid this threat to your health and well-being.