By Gabe Mirkin, M.D.
Cold weather is associated with an increased incidence of heart attacks (Arch Intern Med, 2004;164(8):863-870). The majority of cold weather deaths are associated with elevated blood pressure and increased clotting to cause heart attacks and strokes. If you have heart or lung disease, you are far more likely to die in cold weather than in the heat (Lancet, May 10, 1997;349(9062):1341-6). Even a short-term drop in air temperature in the tropics is associated with increased heart attack risk (Science of The Total Environment, Aug 18, 2022;850(1):158010).
Researchers collected data for 384 locations in Australia, Brazil, Canada, China, Italy, Japan, South Korea, Spain, Sweden, Taiwan, Thailand, UK, and USA, and found that 7.3 percent of deaths from 1985 to 2012 were due to cold weather while only 0.4 percent were due to hot weather (The Lancet, July 25, 2015;386(9991):369–375). A drop in temperature is far more lethal than when it rises too high (BMC Public Health, January 15, 2009;20099(19)). Any drop in air temperature can trigger a heart attack in susceptible individuals (Eur Heart J, Aug 2017;38(1):ehx504.2949).
How Cold Weather Can Cause Heart Attacks
• Cold temperatures cause your body to produce large amounts of adrenalin which constricts your arteries to raise your blood pressure and to make your heart beat faster. If you have damaged arteries or heart muscle, your heart can start to beat irregularly and you can die.
• Cold thickens your blood and makes it more likely to clot. A clot can shut off blood flow to the heart to cause a heart attack (BMJ, 1984; 289: 1405–1408).
• Cold causes the liver to make more fibrinogen that increases clotting (Lancet, 1994; 343: 435–439).
• Cold raises blood cholesterol levels (Am J Med, 1986; 81: 795–800).
• A drop in body temperature weakens your heart muscle, and people with weak or damaged hearts can go into heart failure and die. Winter also deprives many people of sunlight and vitamin D which weakens the heart muscle.
How Cold Weather Can Damage Your Lungs
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 the 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. Exercise-induced asthma 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 develop 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. More about Frostbite
People with Raynaud’s phenomenon have their hands turn white and hurt when they are exposed to temperatures below 60 degrees because their blood vessels do not constrict as norml blood vessels do. 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. They often hurt also when they put their hands in cold running water. Researchers at the Army’s Research Institute of Environmental Medicine had Raynaud’s sufferers sit out in the cold with their hands immersed in warm water six times a day. This caused blood vessels in their hands to open while those elsewhere in the skin closed down. The people who were tested were able to be out in the cold without feeling pain in their hands after eight sessions done every other day.
The blood pressure drugs called calcium channel blockers, such as Nifidipine, can help to treat and prevent Raynaud’s phenomenon (Rheumatology, November 2005). Another option is nitroglycerin ointment that is used to treat angina. When applied to the forearm, it opens blood vessels leading to the hands. Check with your doctor to see if these prescription medications might be appropriate for you. More on Raynaud’s Phenomenon
Hypothermia is a severe drop in body temperature. If you dress properly and exercise vigorously enough, it shouldn’t happen to you. Your body sends you signals as your temperature starts to drop. With a one degree drop in body temperature, your speech can become slurred. This, in itself, is not dangerous, but it serves as a warning that you are losing more heat than your body is producing. To protect yourself, you can produce more heat by exercising harder or you can conserve heat by adding more layers of clothes or seeking shelter.
With a drop of three degrees, you will find it difficult to coordinate your fingers. Seek shelter immediately. When your temperature drops five degrees, you won’t be able to walk and may fall and not be able to get up. Then you may not be able to get out of the cold and your body temperature will continue to drop rapidly and you can die. If your clothes are wet, your temperature will drop even faster. Take the warning signals seriously. If you have slurred speech or difficulty using your hands, take immediate action or you may not get another chance.
If you suffer from heart or lung disease, you should be very careful about exercising in cold weather. Breathing dry cold air constricts arteries and increases clotting to increase heart attack risk, and constricts bronchial tubes to reduce oxygen intake through the lungs. When the temperature drops, people with known heart disease or lung disease are safer exercising indoors where they can breathe warmer air.
Gabe Mirkin, M.D., is a sports medicine doctor and fitness guru. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin has run more than 40 marathons and is now a serious tandem bike rider with his wife, Diana. His website is http://drmirkin.com/. Click to read Gabe’s full bio.
Jordan A. says
Last January, I had a heart attack, foreshadowed by chest pains on my rides late in the 2021. My cardiologist recommended an angiogram, but before I could have that done I had my attack. I spent 4 days in the hospital during which they found a 95% blockage of my LAD artery. I was lucky. I had three stents placed in the artery and have been back on my bike since February riding 3-4 times a week and getting in 100-120 miles/week. I have definitely been affected on rides by the medications I take, and have experienced some lessening of stamina on some of my rides, often depending on the temperature. I live in NC where the temperature in the winter usually hovers and tops out in the low to mid-50s most of the year; however, on some rides the starting temperature can be in the mid-40s. Am I at any risk of another heart attack in temperature ranges like that? I am in regular contact with my cardiologist and with the cardio rehab folks at UNC, but I was curious what you would recommend. Thanks.