This winter is more dangerous than previous winters because cold weather increases your risk for COVID-19, since it increases the time that people spend indoors where the virus can accumulate in the air. More than 95 percent of COVID-19 appears to be acquired indoors, particularly where people congregate. The World Health Organization warns that the virus can be transmitted in any kind of weather, and there is no evidence that cold weather will kill the virus.

Even without considering COVID-19, you are more likely to die from cold weather than hot weather (BMC Public Health, January 15, 2009;20099(19)); cold weather kills about 20 times as many people as hot weather does (Lancet, July 25, 2015;386(9991):369-375). Most cases of cold weather deaths are from its effects on the heart and lungs, leading to heart attacks or pneumonia. People who have chest pain from reduced blood flow to the heart are at increased risk for heart attacks in cold weather, particularly when there are also high winds, snow and rain that can lower body temperature, or when they shovel snow (BMJ, Aug 10, 2010). Major risk factors for sudden death in cold weather are:
• elevated blood pressure,
• elevated cholesterol and
• increased clotting.
Clots cause heart attacks, and high blood pressure and cholesterol damage arteries to cause heart attacks.

People who suffer from heart or lung disease are at higher risk for dying in cold than hot weather (Lancet, 1997 May 10;349(9062):1341-6). A 12-year follow up of more than 220,000 cases found that for every one degree Celsius drop in temperature (that’s 1.8 degrees Fahrenheit), there is a 0.49 percent increase in deaths from all causes (Circulation, Oct 12, 1999;100(15)).

How Cold Weather Can Cause Heart Attacks
Heart attack risk is greatest on days when the temperature is below freezing (JAMA Cardiol, 2018;3(11):1081-1089). There is a 31 percent increase in heart attacks in the coldest months of the year compared with the warmest months (PLoS One, November 6, 2015). Cold weather:
• increases heart attack risk markers of inflammation such as increased neutrophils, white blood cell count (WBC) and C-reactive protein (CRP), and markers of clotting such as increased platelets (PLoS One, November 6, 2015).
• causes the liver to make more fibrinogen that increases clotting (Lancet, 1994; 343: 435-439). A clot can shut off blood flow to the heart to cause a heart attack (BMJ, 1984; 289: 1405-1408).
• increases your body’s production of adrenalin which constricts arteries to raise blood pressure and to make your heart beat faster.
• raises blood cholesterol levels (Am J Med, 1986; 81: 795-800).
• can drop your body temperature to weaken your heart muscle, and people with weak or damaged hearts can go into heart failure.
• decreases exposure to sunlight which lowers vitamin D levels to weaken the heart muscle.

Exercise-Induced Asthma
Almost 20 percent of North Americans have exercise-induced asthma, which usually is caused by breathing dry cold air, not by exercise. When these people breathe dry cold air, the muscles around the tubes that carry air in and out of their lungs can constrict to make them short of breath. Exercise-induced asthma can occur in people who do not have asthma otherwise. It affects almost 50 percent of elite cross-country skiers, ice skaters and hockey players. It is far more common in winter athletes than in those who compete in the summer. Dry cold air also increases risk for common winter infections such as colds or influenza, which cause inflammation that can damage arteries to increase risk for heart attacks.

Tips for Outdoor Exercise in Cold Weather
• If you have heart disease, your doctor probably will recommend that you should not exercise outdoors in temperatures below 50 degrees Fahrenheit.
• Exercising in cold weather can cause chest pain in some people who have no problems when they exercise in warm weather. When cold wind blows on your face, your heart rate slows down. This decreases the blood flow to the heart and can cause pain in people with blocked coronary arteries. While freezing your face slows your heart, freezing your fingers makes your heart beat faster. Cold hands will not cause chest pain, but a cold face can.
• Air is an excellent insulator, and layering clothes traps air. Wear a silk or loosely-woven polyester inner layer that wicks sweat away from your body. Loosely woven wool or synthetic-fiber sweaters or vests are a good middle layer because they trap insulating air and wick moisture to the outside. The outer layer material should be tightly woven so it blocks the wind; a waterproof rain jacket can perform this function. Nylon and Gore-Tex are outstanding because they can be extraordinarily light and still block the wind. Winter jackets do not need to be heavy, they just need to provide insulation and a barrier from wind and rain.
• You feel cold most in your fingers, ears and toes, so be sure to cover these areas. During World War II, gunners on bombers complained bitterly about frozen hands, ears and toes. Special insulation was added to their gloves, hats and boots, and they stopped complaining, but they suffered frostbite on their necks and chests. They had unzipped their jackets because they didn’t feel cold.
• To help keep your hands warm on cold days, wear mittens that do not let wind or water in. The single compartment of mittens retains heat better than gloves that have separate compartments for each finger. If your hands still feel cold, swing your arms around rapidly from your shoulders with your elbows straight. This motion imitates a centrifuge that will drive blood toward your fingers and open up the blood vessels in your hands. You can buy single-use hand heating packets such as “HotHands,” online or in sporting goods stores, and rechargeable warmers are also available.

You should never get frostbite because you get plenty of warning. Get out of the cold if your skin starts to burn or itch. Your normal skin temperature is a degree or two below the internal body temperature of 98.6 degrees F. When your internal body temperature starts to drop, your brain tries to preserve heat by sending a message to the nerves in your hands and feet to close the blood vessels there. With decreased blood flow, the skin temperature of your hands and feet drops rapidly. When your skin temperature reaches 59 degrees Fahrenheit, your brain sends signals to open up blood vessels in your hands, causing your fingers to turn red, burn and itch. This is called the “hunting response” and is normal. You should get out of the cold immediately when your hands or feet turn red and start to itch and burn. If you don’t get out of the cold, the blood vessels in your hands and feet will close down again and the temperature will continue to drop even more rapidly to below freezing. You will suffer frostbite and may lose your fingers and toes.

Raynaud’s Phenomenon
People with Raynaud’s Phenomenon have their hands turn white and hurt when they are exposed to temperatures below 60 degrees because they do not have the “hunting response”. The blood vessels to their hands do not open as soon as their skin temperature in their hands drops to 59 degrees F and their hand temperature drops rapidly toward freezing. Researchers have tried various treatments, but today the most practical solution is hand warmer packets, available in sports stores and online.

My Recommendations
Since COVID-19 is transmitted mostly from breathing infected indoor air, I recommend limiting or avoiding indoor exercise in groups, and to avoid using indoor exercise equipment that is shared with other people. Until you get your vaccine, it will be safer to exercise outdoors or in your home. Without considering COVID-19, exercising in very cold weather can harm people who suffer from heart or lung disease. You may want to treat yourself to a new indoor exercise device to make your exercise program more fun, challenging and comfortable for you.
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