Why Does Cold Weather Increase Your Risk for Heart Attack?

Written by Dr. Joseph Mercola Fact Checked

heart attack

Story at-a-glance -

  • Your risk of heart attack rises with exposure to the cold as your blood pressure and risk of dehydration increase; drinking a caffeinated beverage may also temporarily spike your blood pressure and overload your cardiovascular system
  • While there are significant health benefits to cold exposure under controlled conditions, those over 55 are at greatest risk for a heart attack while exercising or shoveling snow
  • Those who have asymptomatic arterial blockages unable to meet the rising demand of physical activity in the cold weather are also at increased risk for heart attack
  • Additional hazards from cold and frigid temperatures include frostnip, frostbite, slips and falls and hypothermia
  • Take precautions when outside as the temperature dips below 32 degrees Fahrenheit by dressing in layers, covering your head and hands, wearing sturdy shoes with traction and ensuring someone knows where you are and when to expect you back

A number of bodily changes occur when you are exposed to cold temperatures. Although irritating and sometimes embarrassing, a runny nose in the cold weather is actually one way your body protects your mucous membranes.1 The additional fluid helps catch bacteria, viruses and other foreign bodies, which then leave as the mucus drips out of your nose.

The winter months are also a time when your skin tends to dry out, leaving it feeling tight, rough and itchy. Aside from being uncomfortable and less than aesthetically desirable, when it becomes severe, it can crack, making it a perfect entryway for germs. Although external variables contribute to dry skin, including omega-3 fats in your diet can help soothe irritated skin.2

On the other hand, one of the simplest strategies to improve mitochondrial function may be exposure to the cold. Called cryotherapy, cold exposure increases your body’s metabolic rate and induces the production of brown adipose tissue. This is incredibly mitochondrial dense fat that helps your body generate heat and lower your blood sugar and insulin resistance.3

However, before jumping into a snowbank this winter or choosing to exercise when the temperature dips below freezing, it is important to note researchers have identified an increased risk of heart attack occurring when temperatures plummet.4

Cold Weather Conditions Increase Risk of Heart Attack

The research was designed as a prospective, population-based, nationwide data gathering study, during which researchers collected daily weather data from the Swedish Meteorological and Hydrological Institute.5 They also extracted all myocardial infarction reports from the Swedish Nationwide Coronary Care Unit registry between the years 1998 and 2013.

Any patient admitted to any coronary care unit in Sweden with a myocardial infarction was included, totaling over 280,800 patients. Weather data was available for over 274,000 patients, which comprised the population in the final data analysis. The researchers had health information including age, body mass, smoking status and echocardiogram findings.6

The scientists were able to link an increased incidence of heart attacks to lower air temperature, lower atmospheric pressure, higher wind velocity and shorter duration of sunshine. Although they found each was associated with statistically meaningful increased risk of a heart attack, the data supporting the most pronounced effect was from lower temperatures.

As the temperatures rose the rates of heart attacks declined. Dr. Nisha Jhalani of the Center for Interventional Vascular Therapy at New York-Presbyterian/Columbia University Irving Medical Center says these findings support the results of previous research. Jhalani also stated:7

“One thing that’s interesting about this study is that they didn’t just look at temperatures. They looked at a number of other factors, such as sunshine hours and wind velocity. It’s also a nationwide study with a lot of patients.”

Cold Temperatures Affect Arterial Resistance

The initial response to exposure to cold is strong capillary vasoconstriction in the skin, which quickly shunts blood to the interior of the body to maintain warmth.8 Rerouting blood protects vital organs against falling temperature, but diminishes flow in peripheral parts of your body, such as your fingers, toes, nose and face, reducing tactile sensitivity, manual dexterity and gross motor function.

It also makes these areas more vulnerable to frostbite, which happens when the fluid around the tissue freezes. Under optimal conditions, the blood vessels in the skin open and close periodically in order to temporarily increase temperature in the fingertips. This has been called the hunting response, or cold induced vasodilation.9

Cold also increases arterial resistance, triggering cardiovascular complications, such a stroke, myocardial infarction and heart failure. Cold temperatures appear to increase the activity of the sympathetic nervous system, which then initiates cold-induced hypertension and suppresses the expression and formation of nitric oxide.10

This combination of events increases arterial resistance and blood pressure. Jhalani explains the importance of the rise in blood pressure as it relates to the increased risk of heart attacks or stroke, saying:11

“In someone with 70 to 80 percent blocked arteries — which might not be causing any symptoms normally — the arteries can be clamped down enough that the blood supply doesn’t match demand.”

Past research has documented an increase in blood pressure with exposure to cold weather. Researchers found an increase in systolic blood pressure especially pronounced in those over 80.12 There is some variation in the reaction to cold as taller people become colder faster as a larger surface area increases heat loss.

Although exposure may present a significant risk to those with arterial blockage, several countries take cryotherapy very seriously. Those in Japan use it to treat pain and inflammation from rheumatic conditions and individuals in Finland and Russia are passionate about winter swimming.

Finnish researchers have reported the results of a study using 10 women who took cold water plunges for three months. Blood testing revealed a two- to threefold jump in norepinephrine levels minutes after cold exposure, a chemical in the nervous system that may play a role in pain suppression.13

Caffeinated Drinks May Boost Risk Further

An increased frequency in heart attacks during the winter months is related to an increased load on the heart. Those at risk should stay warm and wrap up well before going outside.14 There is also a greater risk of heart attack in the morning hours. Those who combine cold temperature with physical exercise, and who are susceptible, increase their risk of heart attack even further.

Shoveling snow is associated with nearly 100 fatal events in adults and children each year. A recent study found an average of over 11,000 snow shoveling related injuries in medical emergencies treated in U.S. emergency departments each year.15 Most of the injuries are related to bumps, bruises, cuts and broken bones to the back, head, arms and hands.

In those who received emergency treatment, men over 55 were twice as likely as women to get snow shoveling related heart symptoms.16 The same study found healthy young men shoveling snow increased their heart rate and blood pressure more than when they exercised on a treadmill.17 Combined with cold air triggering arterial constriction and increased workload, this may just be the perfect storm.

Snow shoveling is particularly strenuous on the cardiovascular system as it uses upper body work, which is more taxing than leg work. Also, many hold their breath while lifting, placing an additional strain on the heart.

Barry Franklin,18 director of cardiac rehabilitation at Wayne State University and an expert in the hazardous effects of snow removal, advises those over 55 not to shovel snow and believes those at greatest risk have been habitually sedentary with no known or suspected coronary artery disease.

While you may be tempted to come in from shoveling snow and drink a tall hot cup of coffee, this could be the worst thing you could do. Caffeine causes a short, but dramatic increase in blood pressure, even if you don't have high blood pressure.19 Jhalani warns adding caffeine to an already at-risk situation may only increase your potential for experiencing a heart attack or stroke.20

Cold Weather May Create Additional Hazards to Your Health

Yet another stress on your heart is triggered by dehydration as a result of cold diuresis.21 As blood is shunted from your skin to your organs, it increases the volume in your body's core.

The increase in arterial pressure triggers a response in the kidneys to reduce blood volume by removing water to the bladder. If you are already dehydrated, this can create additional stress on your cardiovascular system as your body begins to warm up.22

As the temperature dips below freezing any water will turn to ice, increasing your risk of falling. Under icy conditions, normal footwear may not be enough. Overshoes or boots with an aggressive sole pattern help to reduce slipping and falling.

Cold weather also increases your risk of frostnip and frostbite.23 Frostnip happens as an area becomes so cold that blood flow slows and the skin becomes unnaturally pale. It happens first to your nose, ears, cheeks, fingers or toes. This can lead to frostbite where ice crystals form inside the body's cells, killing them in the process.

Superficial frostbite may be painful but it may not result in the loss of body parts or limbs. Deep frostbite often kills enough cells that an area may have to be amputated. If you suspect frostbite, move somewhere warmer if possible and seek immediate medical attention. Do not rub the area.24

When your body's core temperature falls (hypothermia) it can result in slowed reaction times and impaired judgment. You'll have plenty of warning of hypothermia as you'll be shivering, will have reduced dexterity and will be miserably cold.

Stay Safe and Warm in Cold Weather

If you have determined to exercise outdoors or to shovel snow, it is prudent to be cautious. Dressing appropriately and paying attention to the following safeguards may keep you safe and warm:

  • Dress in three or more layers — Avoid heavy cotton material as it absorbs sweat and traps wetness, increasing your risk of hypothermia. Add a second layer of wool or fleece for insulation and an outer layer of lightweight, water-repellent, wind-resistant material. Lightly colored or reflective clothing at night helps ensure you are visible to drivers.
  • Cover your head and extremities — You lose 50 percent of your body heat from an uncovered head. Layering thin gloves with heavier mittens helps if you need to remove a layer without exposing your bare skin to the frigid air. Cover your face with a mask or scarf when the temperature is below freezing, which may help warm the air before entering your lungs.
  • Wear proper footwear — Sturdy shoes or overshoes with an aggressive grip help prevent slips and falls on the ice and snow.
  • Stay hydrated — Drink enough fluids to keep your urine a light straw color. Proper hydration is as important during cold weather as hot weather. Drink before and after being outside, even if you don’t feel thirsty.
  • Stay dry — Dressing too warmly when shoveling snow or exercising in the cold weather is a common mistake. Exercise generates body heat. Once sweat begins to accumulate it may freeze and contribute to lowering your body temperature. Remaining dry is equally important as being warm, so using a wicking layer closest to the skin helps reduce the impact.

When you leave, tell someone what route you're taking if you’re exercising, and when to expect your return, just in case something goes wrong. If you slip and fall in the winter, hypothermia can be deadly if no one knows to look for you.

Keep in mind wind chill may make exercising riskier, even if you dress warmly. As a general suggestion, I recommend taking a break from outdoor activities if the temperature dips below zero degrees Fahrenheit (-17.8 C), or if the wind chill factor is high.