How do cold health alerts work and what do the different levels mean?

Amber and amber alerts have already been issued for colds across much of England this winter.

Warnings alert the public when low temperatures pose a potential health risk.

The weather alert service is run by the UK Health Security Agency (UKHSA) and the Met Office.

Cold weather health warnings are issued from November 1 to March 30, and heat warnings are issued from June 1 to September 30.

As well as warning the public, the system sends advice directly to NHS England, government and health professionals during periods of severe weather.

Warnings are classified by severity and include:

• major weather conditions expected in the coming days
• Details on how weather conditions will affect each region
• links to additional information, tips and tricks

The system was designed to help reduce morbidity and mortality during periods of extreme hot and cold weather.

The alert level is based on Met Office forecasts and data.

There are four levels, from green (least serious) to red (most serious):

Green

Green is the normal level, which provides advice on how people should prepare to respond if temperatures rise or fall.

Yellow

Yellow warnings are issued during periods of hot or cold weather that may only affect those who are particularly vulnerable, such as the elderly or people with existing health conditions.

Amber

Yellow warnings are issued in situations that could potentially put the entire population at risk. For example, the NHS could see increased demand for GPs and ambulances.

Travel disruptions are also likely.

Red

The red alert level is the most severe.

It is issued in situations where hot or cold weather could pose a significant risk to the lives of even healthy populations and could result in disruptions to critical national infrastructure, such as power outages or closures of roads and railway lines.

The flu and some other illnesses that cause colds and sore throats spread more easily during the winter months. Pneumonia, when infection causes inflammation in the lungs, is more likely to occur after cold weather.

Cases of norovirus, the winter sickness virus, are also trending upward.

Professor Damian Bailey from the University of South Wales produced the program for BBC Radio 4's Inside Health. About the effect of cold on the body.

Presenter James Gallagher spent 30 minutes in a room where the temperature dropped from 21 to 10 degrees.

During the experiment, his blood flow to the brain decreased, his blood pressure and heart rate increased, the temperature of his extremities – arms, legs and head – decreased, and it took him significantly longer to solve a series of puzzles.

Professor Bailey said a temperature of 18°C ​​is a tipping point for the body: below this temperature the body has to work harder to maintain its internal temperature. This is one reason why heart attacks and strokes are more common during the winter months.

When it is not possible to keep the room temperature to 18°C, he recommends wearing gloves, warm socks and a woolen hat, eating a high-carbohydrate diet and generating more body heat by moving.