Thunderstorms

Asthma, headaches, migraine, allergies, mood Asthma rates can soar within 60 minutes of a thunderstorm. Research at Imperial College into the effects of one storm in London shows: "A sudden and extensive epidemic occurred within about an hour, affecting possibly several thousand patients." Most of these people were found to have antibodies to grass pollen but the researchers were unable to conclude exactly how storms increase asthma attacks. A second study suggests pollen grains are ruptured by the thunderstorm, releasing large amounts of concentrated inhalable allergens.

Humidity

Headaches, migraine, ear wax, sickle-cell anaemia, insomnia, gout, respiratory viruses, rheumatoid arthritis More than half of headaches are triggered by weather, say researchers at the Children's Hospital in Boston. In their study group, one in three headaches were caused by changes in humidity and temperature, while 13% developed as a result of changes in barometric pressure. A study at Kingston University, Surrey, shows painful sickle-cell anaemia symptoms increase when humidity is low and wind-speeds are high, as a result of the weather conditions cooling skin.

Research at Nahdha Hospital in Oman shows that people living in areas with high humidity are twice as likely to have problems with ear wax, while work in Boston shows attacks of gout are more frequent on days of high humidity, possibly because of the effects of dehydration.

Sun

Cancer, seasonal affective disorder, pain, fertility, diabetes, heart disease, high blood pressure, multiple sclerosis, psoriasis Sun exposure may increase survival chances for cancer patients. Research shows women diagnosed with breast cancer in the summer have a 14% higher chance of survival than those diagnosed in the winter, while men and women found to have lung cancer in the summer had a 5% lower risk of dying.

Sunlight is essential for the production of vitamin D in the body and one explanation could be that this vitamin helps stop the growth of tumours. Meanwhile, scientists at the Naval Health Research Center in San Diego found that the right levels of vitamin D halve the risk of colon cancer and doctors at the University of Milan found that patients admitted with clinical depression who were allocated hospitals beds with high levels of sunlight in the mornings went home 3.67 days earlier than average.

Rain

Mood, plague, water-borne infections, headaches, respiratory problems Research at the University of New Mexico shows that cases of plague in humans occurred more frequently in years when rainfall was 13% above normal. Their conclusion is that the moist environment means more disease-carrying fleas survive and reproduce. A study at Trinity College Dublin shows that rainfall has an effect on mood and on the buying of stocks and shares, while researchers at Canada's University of Guelph have found that water-borne infections including E coli increase after heavy rainfall.

High rates of dampness have been linked to headache and respiratory problems, while levels of negative ions the air after a storm may also affect mood.

Cold

Heart disease, Raynaud's phenomenon, depression, stroke, low birth weight, knee pain, Bell's Palsy Reports from a number of centres, including Boston University, have found links between cold weather and an increased risk of cardiovascular disease.

One of the theories is that blood moves more slowly in colder temperatures and is therefore more prone to clotting, especially in arteries already narrowed by disease. A study at Uppsala University, Sweden, shows cold summer days have an effect on health, too, with antidepressant use increasing significantly on colder days in the summer months. A report from the US National Institutes of Health shows summer babies tend to be of lower weight, probably because of the effects of cold temperatures in the early stages of the pregnancy. And researchers at La Paz Hospital in Madrid found the numbers of cases of Bell's Palsy rose in colder weather.

Wind

Mood, headaches, depression, flu, hot flushes, sickle-cell anaemia, insomnia Studies in Austria show high winds lead to a 20% rise in suicides. More than one in three people surveyed by Germany's Allensbach Institute said wind affected their health. One theory is that the changes are as a result of electrically charged air. Negatively charged air has been shown to improve mood . . . warm winds are more positively charged.

Heat

Premature death, dehydration, crime, respiratory disorders Just like excessive cold, too much heat can also cause a premature death. A study at Fudan University, Shanghai, found that a 10C rise in average temperature over three days led to a 37% increase in mortality rates, a conclusion borne out by the higher death rates across Europe during the heatwave of 2003. The Italian National Institute of Health saw expected mortality rates rise by 15%, while in the UK it's estimated there were 619 more deaths than usual during that 31-day heatwave. There is also an increased risk of bad behaviour and rioting with temperature. According to a Manchester University report, temperatures of 270C, 290C, and 340C have been identified as "riot temperatures".