Researchers collected data for 384 locations in Australia, Brazil, Canada, China, Italy, Japan, South Korea, Spain, Sweden, Taiwan, Thailand, UK, and USA, and showed 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). Other studies show that having the temperature drop too low is far more lethal than when it rises too high (BMC Public Health, January 15, 2009;20099(19)). If you have heart or lung disease, you are far more likely to die in cold weather than in the heat (Lancet, 1997 May 10;349(9062):1341-6).

The majority of cold weather deaths are from its effects on the heart and lungs to cause heart attacks or pneumonia. The major causes of sudden death in cold weather are elevated blood pressure and increased clotting. High blood pressure damages arteries to cause heart attacks and strokes. If you have blood vessel disease, heart disease or lung disease, try to stay out of the cold.

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. 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.

Rules for Exercising in Cold Weather
1. If you have active severe heart disease, your doctor probably will recommend that you should not exercise in temperatures below 50 degrees Fahrenheit.

2. 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. See my report on Angina (above). 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.

3. Air is an excellent insulator and layering clothes traps air. Wear a silk or loosely-woven polyester inner layer that wicks sweat rapidly away from your body. Loosely woven wool or polyester sweaters or vests are a good middle layer because they trap insulating air and wick water rapidly 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. Modern jackets do not need to be heavy, they need to provide insulation and a barrier from wind and rain.

4. 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.

5. 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 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 Phenomonon 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. 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. More on Raynaud's Phenomenon