Few things are more invigorating than a dip in the ocean, a lake, or any cool body of water, especially during late summer’s heat. A rare breed of hardy souls — mostly extreme athletes — even seek out ice-swimming competitions in the winter.
Some people swear by the health perks of cold-water immersion, which allegedly includes fat loss, improved sleep, and reduced inflammation — all of which may benefit cardiovascular health. But so far, the evidence is pretty shallow.
“We have a good understanding of the immediate effects of cold-water submersion on the body. But the research looking at health outcomes from repeated exposure to cold water is quite limited,” says cardiologist Dr. Aaron Baggish, director of the cardiac performance lab at Harvard-affiliated Massachusetts General Hospital. Most people who enjoy cold-water swimming can do so safely, provided they always swim with a partner. But those with history of heart rhythm abnormalities should avoid cold-water dips, he says.
The diving reflex
When you put your face in water — particularly cold water — the nerve receptors in your nose and mouth send a signal to your brain that you’re in water. Your brain then tells your body to redistribute blood from your extremities (arms and legs) into your chest and brain to conserve oxygen, Dr. Baggish explains. This well-known phenomenon, called the diving reflex or diving response, causes your heart to slow down dramatically and your blood pressure to rise. The term is a bit of a misnomer because the reflex occurs at the water’s surface and doesn’t require diving per se. But the colder the water, the greater your body’s response.
Even if you don’t put your face in the water, the shock of cold water against your skin sets off the body’s “fight-or-flight” response. The resulting surge of adrenaline causes blood vessels supplying the skin to narrow. This conserves heat but shifts even more blood to the chest, taxing the heart.
Heart rhythm risk
Extra adrenaline can also disrupt the heart’s steady rhythm, although this usually isn’t a problem in someone with a healthy heart. People who aren’t accustomed to chilly water may have a more exaggerated response initially, but they generally acclimate over time. And what people consider to be cold can vary, of course (see “A little chilly — or the big chill?”)
“I get a lot of questions about Boston’s annual polar bear plunge. The only people I advise against doing it are those with a heart rhythm abnormality such as atrial fibrillation,” says Dr. Baggish. Both the fight-or-flight response and the diving reflex may trigger an underlying arrhythmia to appear, he adds.
|A little chilly — or the big chill?We normally think of 70° F as a pleasant temperature. But that’s air, not water temperature. Lap swimming pools are usually set between 78° and 82°, which is similar to the water temperature along Florida’s beaches in August. West Coast beaches are much cooler; even in southern California, the Pacific Ocean is only about 68° in the summer.For most people, anything under 70° will feel decidedly brisk. But open-water swimming enthusiasts don’t mind the chilly temps, although some don neoprene wet suits when the temperature falls below 65° or 60°.But that’s practically balmy compared with the water at most polar bear plunges, which are a New Year’s Day custom in many communities across the country. At the one in Boston Harbor (a tradition since 1904), the water temperature hovers around 42°.|
It’s not clear whether cold-water swims have any effect on inflammation connected to cardiovascular disease. But athletes often immerse themselves in ice-cold water immediately after a workout to reduce tissue inflammation and injury caused by intense exercise, Dr. Baggish notes. The cold causes blood vessels in the limbs to constrict, and the resulting reduced blood flow dampens inflammation. Even though the effect is temporary, it’s a great way to minimize muscle discomfort the next day, he adds.
Bible verses for today’s meditation and inspiration: Matthew E. McLaren
Yours, Lord, is the greatness and the power and the glory and the majesty and the splendor, for everything in heaven and earth is yours. Yours, Lord, is the kingdom; you are exalted as head over all. 1 Chronicles 29:11 NIV
Love the Lord your God with all your heart and with all your soul and with all your mind and with all your strength. Mark 12:30 NIV
Now to him who is able to do immeasurably more than all we ask or imagine, according to his power that is at work within us, to him be glory in the church and in Christ Jesus throughout all generations, for ever and ever! Amen. Ephesians 3:20-21 NIV
So he said to me, “This is the word of the Lord to Zerubbabel: ‘Not by might nor by power, but by my Spirit,’ says the Lord Almighty.” Zechariah 4:6 NIV
For the message of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God. 1 Corinthians 1:18 NIV
For who is God besides the Lord? And who is the Rock except our God? Psalm 18:31 NIV
It was not by their sword that they won the land, nor did their arm bring them victory; it was your right hand, your arm, and the light of your face, for you loved them. Psalm 44:3 NIV
For since the creation of the world God’s invisible qualities—his eternal power and divine nature—have been clearly seen, being understood from what has been made, so that people are without excuse. Romans 1:20 NIV
For in Christ all the fullness of the Deity lives in bodily form, and in Christ you have been brought to fullness. He is the head over every power and authority. Colossians 2:9-10 NIV
Recommended contacts for prayer request and Bible study