How long could you comfortably stay underwater without coming up for air? Thirty seconds? Maybe a couple of minutes? How about 24?

That is the current world record for breath-holding held by Alex Segura Vendrell of Spain. Before you get any ideas for your next party trick, it’s important to note that Segura Vendrell is a professional freediver and trained extensively for those 24 minutes and 3.45 seconds.

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How is it possible to hold your breath that long?

It turns out that holding one’s breath for an extended period of time, also known as voluntary apnea, is somewhat of an extreme sport in and of itself. Professional divers and competitors train by taking deep breaths before submerging themselves. By holding a big breath before going underwater, a diver is able to push the carbon dioxide out of his or her body, which takes away the body’s natural reaction to come up for air.

Sounds dangerous, right?

How long is it safe to hold your breath?

According to the Canadian Red Cross, most healthy adults can comfortably hold their breath for about one to two minutes. Anything beyond this is dangerous and should be avoided and can put you at risk for drowning, even in shallow water. Breath-holding underwater is just one of the things lifeguards wish you wouldn’t do. Here are just a few of the processes going on in the body when you hold your breath.

Your oxygen levels go down

Without fresh oxygen coming into our bodies, the oxygen saturation level of our blood goes down. This means that our brain and organs do not receive the oxygen they need to function. When our brains begin to become hypoxic, the first symptoms are a feeling of confusion, altered decision making, and loss of coordination.

Your carbon dioxide levels (should) go up

If you were to hold your breath right now, your blood’s oxygen level would start to decrease and its carbon dioxide level would go up. Our bodies release carbon dioxide when we exhale, so as we hold our breath, it builds up and causes us to feel the urge to take another breath. However, this increase in carbon dioxide doesn’t always happen underwater.

A study in the European Journal of Applied Physiology found that when divers intentionally hyperventilate or exercise before going underwater, their carbon dioxide levels are slower to go up. This can put the diver at risk of passing out before feeling the need to come up for air.

You could be at risk for brain damage

A study in the Journal of Applied Physiology found that when divers held their breath for extended periods of time, they had higher levels of the protein S100B in their bloodstream. This protein is a marker for brain damage; fortunately, the increased level was temporary and went back to normal once they started breathing again.

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“The results indicate that prolonged, voluntary apnea affects the integrity of the central nervous system, and may have cumulative effects,” explained the researchers. It’s unclear if people who regularly hold their breath, such as divers, are at risk for long term damage.

You could lose coordination

The study in the Journal of Applied Physiology also found that divers had higher levels of lactate in their blood while holding their breath. Lactic acid is what builds up in your muscles during a long run or intense workout and can lead to cramping, soreness, and loss of coordination. Seeing this increase in the bloodstream means that the muscles are not receiving enough oxygen. Learn more obscure body facts you didn’t know.

Your blood sugar goes up

Holding your breath for too long can cause your blood sugar to jump. Researchers found that blood glucose levels were higher in divers when holding their breath. It’s unclear why blood sugar rises when the body is deprived of oxygen, but it may be related to our body’s inability to secrete insulin during that time.

Your heart rate slows down

When our bodies are deprived of oxygen, the heart can’t pump fresh, oxygenated blood out to the body. Studies show that about 30 seconds of breath-holding can lead to a lowered heart rate and lower cardiac output.

Your blood pressure goes up

Once your body’s heart rate goes down during breath-holding, it tries to compensate by raising your blood pressure to get blood pumped to the body. This happens as our blood vessels constrict. This blood pressure increase usually happens after three minutes of breath-holding, once the oxygen level in our blood starts dropping.

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You could pass out

The dangerous risk of holding your breath underwater is the chance of passing out in the water. According to experts at Emory, when children hold their breath underwater, the pressure in their chests causes their blood vessels to cut off blood flow to the right side of the heart. When this happens, the heart can’t pump blood, which leads to the reflex to faint. Adults who hold their breath for extended periods underwater are also at risk of passing out.

Stay safe around water

Because of accidental drownings related to healthy children and adults holding their breath underwater, the U.S. Centers for Disease Control and Prevention recommend never practicing voluntary apnea. Be sure to teach your kids to stay safe when swimming and never play breath-holding games with friends.

This article first appeared on Reader's Digest.