The causes vary, and include increased susceptibility to flu and other viruses.
However, hypothermia is one of the most deadly cold-induced conditions and, if not caught and treated early on, can lead to a rapid decline in the body's ability to function normally.
What is it?
Hypothermia occurs when the body's core temperature is lowered due to exposure to cold.
It can occur even at mild temperatures if exposure is prolonged.
The body's natural defences against the cold consist of restricting the flow of blood to the skin so as to prevent heat loss, along with shivering and releasing hormones to generate heat.
These measures are limited and are usually inadequate to maintain body temperature in cold environments.
What are the symptoms?
Symptoms take effect in three stages.
The first stage - mild hypothermia - is characterised by:
Bouts of shivering, grogginess and muddled thinking.
Indicators of moderate hypothermia are:
Violent shivering or shivering which suddenly stops, inability to think and pay attention, slow, shallow breathing, slow, weak pulse.
Severe hypothermia has set in when:
Shivering stops, the patient loses consciousness, there is little or no breathing, pulse is weak, irregular or non-existent.
Who is at risk?
The elderly and babies under one year old are most at risk among people with no other complaints. However, people who already have something wrong with them are also at a higher risk, as they may not be aware of how severely they are exposing themselves to the cold.
The main risk groups are:
People who have been involved in accidents;
Mentally ill patients;
People with heart problems;
Patients on sedatives;
Due to their sleeping arrangements, the homeless are also particularly at risk.
People who expose themselves to extreme weather conditions, such as mountain climbers, are at risk, but will usually travel prepared for emergencies. They should also have some understanding of how to recognise and treat hypothermia before they set off.
What is the treatment?
The first step is to contact the emergency services as extreme hypothermia requires urgent professional attention.
All cold, wet clothing should be replaced with warm, dry clothing to prevent further heat loss immediately.
If breathing has stopped or there is no pulse, cardiopulmonary resuscitation (CPR) should be attempted until the emergency services arrive.
Rapid rewarming with hot water or massaging cold extremities should be avoided as, if done improperly, it could lead to serious tissue damage.
Do not give alcohol or nicotine products to someone suffering from hypothermia.
How can it be prevented?
The key rules are to wear many layers of clothing, drink plenty of fluids and hot drinks (but not alcohol) and keep well nourished.
Maintaining movement to keep circulation up is also advised.
Age Concern advises keeping at least one room well-heated during the winter months.