The recent launch of the influenza vaccination campaign is a reminder that the annual round of sniffles, coughs and other respiratory disease is not far away. Equally, as outdoor barbecues and picnics on the beach fade into the memory banks, the risk of foodborne gastroenteritis begins to decline.
A link between the weather and human health has been postulated as far back as 400 BC, when Hippocrates wrote Airs, Waters and Places. He noted the winter link with coughs and pleurisy, while summer brought with it fevers and diarrhoea.
Now, the scientific link between weather and well-being is emerging. Researchers at Reading University compared the number of heart attacks in Oxford with other cities throughout the world. The results show a clear pattern of worsening rates of heart attack occurring with the arrival of both spring and autumn.
The common factor coinciding with the seasonal increase is a sudden temperature change. This places the body under extra physiological stress, which causes heart attacks in some people with pre-existing heart disease.
The Meteorological Office in the UK has set up a dedicated unit to give doctors notice of a likely rise in bronchitis, heart attacks and strokes. The initiative follows last year's viral illness outbreak, which caused a surge in demand for hospital beds. Dr William Bird has been recruited to the UK Met Office in Bracknell in Berkshire to help develop the technique. He is hoping to predict, almost to the day, when large numbers of patients will seek treatment.
We already know that a mild winter spell followed by a sharp drop in temperature is a reliable predictor of illness. About two days after the onset of cold weather, there is an increase of up to one third in the number of heart attacks. Five days later, we see a rise in stroke victims. Twelve days after the cold snap, the number of patients with respiratory illness goes up.
UK figures also show a link between temperature and mortality. For every one degree fall in temperature, there is a 1.4 per cent rise in the death rate. This finding suggests that if people dressed more warmly, exercised more and had better heating in their homes, the trend could be neutralised.
At a physiological level, cold exposure causes the immune system to function less effectively. The extra stress on the heart and the circulation leads to a rise in heart attacks. The blood also thickens in response to cold, which is the mechanism behind the increased risk of stroke.
The onset of autumn and winter sees a rise in a specific form of depression called seasonal affective disorder (SAD). This has been linked to lower levels of production of the brain chemical, melatonin, which depends on sunlight. It has even been suggested that patients with schizophrenia see an increase in their symptoms at times of large temperature swings.
Summer weather bring with it dehydration, which can often trigger the symptoms of kidney stones. Skin cancer has an obvious link with the hazy, lazy days also.
Patients with arthritis almost universally complain of increased pain and joint stiffness during damp and cold weather, although I am not aware of any scientifically proven link.
I do recall an interesting experiment I conducted with a good friend of mine while we were doing our postgraduate medical training. We decided to compare the incidence of asthma in urban and rural areas. In fact, our hypothesis was to try to relate asthma incidence to smog, but as sometimes happens in medicine and science, we actually came up with an unexpected finding.
Regardless of urban or rural location, the asthma patients we studied all disimproved with the onset of thundery weather. We found quite a striking link when we compared their asthma status with Met Office records.
Dr Bird and his colleagues will be looking at possible links between asthma and barometric pressure as part of the Met Office research. It will certainly be interesting to monitor the accuracy of their predictions as autumn and winter progresses.
Contact Dr Houston at mhouston@irish- times.ie or leave messages on tel 01- 6707711, ext 8511.