The Met Office website, http://www.metoffice.com, produces special health forecasts to help professionals and their patients know when and where there is a risk of illness - which, in turn, helps reduce hospital admissions. "For people with some long-term illnesses, changes in the weather can have a direct impact on their quality of life," it says.

One debilitating condition that the Met Office forecasts for is COPD (Chronic Obstructive Pulmonary Disease). Thousands of people in the UK are sufferers; symptoms include breathlessness and coughing, which often worsen in the winter. "Reaching these patients before they become ill can prevent further worsening of their condition, and may reduce the risk of admission to hospital," adds the Met Office.

An individual's response to a certain weather-affected diseases and ailments will vary from person to person, according to various factors such as age. Below are some Met Office facts on colder temperatures and health:

• Acute bronchitis affects young children before Christmas and the over-65s during the New Year period.
  
  
• In England and Wales, there is a 2% increase in mortality for every degree below 19°C. Roughly half of these deaths are caused by respiratory conditions and half by strokes and heart attacks.
  
  
• After a fall in temperature, heart attacks increase after two days, strokes after five days and respiratory disease after 12 days.
  
  
• Most heat-related deaths are caused by respiratory illness and strokes in the elderly.

Asthma

Symptoms can be triggered by, among other things, the weather. Attacks are known to have a seasonal pattern, and thunderstorms are widely implicated.

In 1994, when a large thunderstorm crossed London, there were more than 1,000 asthma attendances at A&E departments. More attacks, some serious, were triggerred in summer 2002 when storms crossed eastern England. "The combination of a previous dry spell, which allows pollen to be sucked into the storm and then deposited in a concentrated area - causing very localised, high levels of pollen - appears to be the cause of these outbreaks," says the Met Office. "The addition of high ozone levels may increase the sensitivity of the lungs, resulting in more-severe symptoms."

Seasonal Affective Disorder (SAD)

The lack of daylight hours and sunlight during the autumn and winter has an adverse effect on an estimated 500,000 Britons each year, creating a specific, seasonal type of depression. Symptoms include sleep problems, lethargy, anxiety, loss of libido and overeating.

Before the invention of artificial lights, we had more natural sleep patterns - we woke up with the dawn and went to bed when it got dark. Modern life, and less daylight, mean the hypothalamus in the brain - which registers changes in light via the retina - adjusts its response accordingly. Among the hypothalmus's roles is the control of our sleep, temperature and mood mechanisms.

The Seasonal Affective Disorder Association says that light therapy is effective treatment in 85% of cases. During the treatment, a patient sits in front of a very bright light (at least ten times the intensity of ordinary domestic lighting) emitted from a home-based light box for between 30 minutes and four hours a day.

Trying to get out into natural daylight as often as possible will help SAD symptoms, especially when the day is at its brightest, and GPs sometimes suggest antidepressants and/or counselling. However, the Association points out that some antidepressants "are counterproductive as they can often cause the main symptoms of the disorder, such as sleepiness and lethargy".

Pea-soupers

We think of our skies as polluted these days, but around 4,000 people died in the London "pea-souper" smog back in December 1952. The tragedy was caused by a combination of frost, fog and still air for several days. Many victims already had chronic complaints such as bronchitis and pneumonia.

We no longer have pea-soupers because the deaths led to the passing of the Clean Air Acts,. Still, other pollutants now clog our cities air - these include less visible nasties such as carbon monoxide fumes from vehicle exhausts.

Hot-weather risks

The heatwave that struck Europe in 2003 killed more than 2,000 people in England. Among these, 85% were people aged 75 and over.

Babies and children aged under four are also at risk because their bodies adapt more slowly to changes in temperature. People who are sick, overweight, have a physical job or consume large amounts of alcohol should also be careful.

Among the dangers are:

• Dehydration: during heatwaves as the body loses vital blood salts such as potassium and sodium. Symptoms include lethargy, confusion and an increased heartbeat.
  
  
• Heat stroke: Usually sweat keeps us cool in hot weather but if we over-exert ourselves, or spend too much time in the sun, the body can't cope and body temperature rises to dangerous levels. Symptoms include headaches, dizziness and muscle cramps. Babies are particularly vulnerable because their sweat glands are not well-developed.
  
  
• Sunburn: Besides ageing the skin, sitting out in the sun until the skin burns, blisters and peels increases the risk of skin cancer.