How does cold weather affect your heart?

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• How cold does it need to be for weather to affect your heart?
• What happens to your blood vessels when you are cold?
• Do people with heart conditions respond differently to the cold?
• What can I do to protect my heart during the winter months?
• How are researchers using cold to help with diagnosis?

How cold does it need to be for weather to affect your heart?

Official statistics on additional (or “excess”) deaths in winter in the UK suggest that the rise in risk starts once the average temperature drops below 12C (54F), although the issue is complex, as this varies according to where you are in the UK, and is influenced by things like home insulation. And cold is not the only factor in excess winter deaths. In recent years, researchers have shown that the effects on health of a cold day or cold spell can be seen for two weeks or more afterwards.

BHF-funded scientists at the University of Bristol and University College London, who looked at records of people aged over 60 in the UK, Ireland and the Netherlands, found that heart attacks and strokes were more than twice as likely to happen during cold spells lasting at least four days. The researchers defined a cold spell as a period that was particularly cold compared to the rest of the month. A fall in temperature compared with the previous days seemed to be the biggest factor, rather than exactly how cold it was. This research and other studies supported by the BHF have been helping us to learn more about how the cold affects our heart and blood vessels.

What happens to your blood vessels when you are cold?

Our heart and blood vessels are always adapting to our environment, and to what is going on inside the body, to keep blood flowing so that different parts of the body get the oxygen and nutrients they need. When we are cold, our nervous system springs into action to stop our core body temperature dropping and to keep our vital organs working.

When you are cold, blood vessels narrow in your skin and fingers and toes, so that less heat is lost. But this narrowing (called ‘vasoconstriction’) creates more pressure in the rest of the circulation, meaning the heart has to work harder to pump blood around the body, increasing heart rate and blood pressure. This is a normal response to the cold, but the extra strain can lead to heart symptoms for people who have an existing condition, especially during exercise.

Our heart and blood vessels are always adapting to our environment, and to what is going on inside the body

When we exercise, our hearts beat faster and with more force, and blood vessels supplying our muscles expand to allow more blood through. At the same time, blood vessels supplying other areas of the body (such as the digestive system) narrow, so that the working muscles get more of the blood flow.

People with angina may experience a worsening in their symptoms during the winter months, or find that they are less able to be physically active when it’s cold. At the same time, the blood itself can become thicker and stickier and more likely to form clots – which can lead to a heart attack or stroke. So if you have a heart condition, it’s important to stay warm in winter. If you find that you feel worse when it’s cold, stay in on the coldest days if you can, and exercise indoors.

• Get more information on how the cold can affect your heart condition
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Do people with heart conditions respond differently to the cold?

BHF-funded researchers at King’s College London have discovered more about why the cold might affect people with .

The study looked at 42 people who had chest pain, 32 of whom had blockages in their coronary arteries (the cause of most types of angina, and of heart attacks). These volunteers inhaled cold air through a face mask, while the blood flow to their heart was measured.

In the people with chest pain who did not have blocked coronary arteries, inhaling cold air increased blood flow to the heart – a healthy response which helps the heart to work harder to keep your vital organs warm. But when people with blocked arteries inhaled the cold air, it caused a drop in the blood flow in the coronary arteries supplying their heart, and there was some evidence that there was less flow of blood within the heart muscle.

So if you have a heart condition, it’s important to stay warm in winter

Some people with blocked arteries were also asked to pedal on an exercise bike. In this group, cycling increased blood flow into the heart – as you would expect - but if cold air was inhaled while exercising, the heart’s blood supply was reduced.

The researchers suggested that people with angina caused by blockages in their coronary arteries should avoid exercise in cold air where possible. This was a small study, so further research is needed.

What can I do to protect my heart during the winter months?

A BHF-funded study looked at risk factors for heart disease in people over 60, relative to the daily average temperature where they lived (in the UK, Ireland and the Netherlands).

They found that on average, the lower the temperature, the higher their cholesterol and blood pressure (which can increase your risk of heart and circulatory diseases) and the lower their vitamin D levels. These changes are probably not directly caused by the cold, but are more likely to reflect how our behaviour changes when the weather is colder.

The same researchers also found that the risk of dying of heart disease in a cold snap was higher in people who drank more than one alcoholic drink a week, or had ever smoked. This research suggests that having healthy habits throughout the year isn’t just good for long-term heart health, it can help to lower the risk that cold weather can pose to your heart, too.

• Read 5 quick tips for eating healthy this winter
• Learn 5 simple ways to boost your heart health during winter

How are researchers are using cold to help with diagnosis?

In some cases, the cold could be useful. Now that we know that the blood vessels might respond differently to the cold in people with heart and circulatory conditions, those differences could be used to develop a way to diagnose a problem with the blood vessels.

Another team of researchers at King’s College London have developed a way to cool a small area of the skin to 10°C (50°F). This drop in temperature is enough to stimulate healthy blood vessels in the skin to contract, and this can be measured. This technique could potentially be used to detect the early stages of blood vessel damage – for example, blood vessels which have been damaged by high blood sugar levels caused by diabetes may not be able to contract as effectively. With BHF funding, the team are testing this technique in mice, to understand more about the detailed processes that cause the cold response, and how the response differs in mice with diabetes. 

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