Summer evenings see drop in stroke rates

By REBECCA WALSH

A study has found Aucklanders are less likely to have a stroke in summer and autumn than in winter or spring.

The study, published in the New Zealand Medical Journal today, says those who suffer a stroke are also nearly three times more likely to experience it in the late morning than in the evening.

The researchers say the results, some of which mirror overseas findings, have implications for provision of acute stroke services in the city.

A total of 1711 patients were registered for the study over a 12-month period. The date and time of onset of the stroke was obtained through an interview with the patient or a relative.

The researchers found the rate of occurrence of stroke was highest in the late morning (between 6am and noon) compared with other times of the day, regardless of gender or age. The risk of stroke in the afternoon (between noon and 6pm) was about two times higher than in the evening.

People's risk of stroke was lowest in the summer when there was a 25 per cent reduction compared to spring. In autumn the risk was reduced 20 per cent compared to spring.

The study found a trend toward an 8 per cent increased risk of stroke in winter compared with spring but it was not statistically significant.

One of the authors, Valery Feigin, associate professor of the Clinical Trials Research Unit at Auckland University, said the finding that most strokes happened in the late morning replicated other studies.

One possible explanation was that a person's blood pressure dropped at night and their heart rate slowed, which could affect blood flow to the brain in those who had medical conditions such as narrowing of the arteries.

It was likely most strokes occurred during the night but patients became aware of them only when they woke, he said.

Associate Professor Feigin said in cold weather blood pressure tended to increase, which could also cause a stroke. Cold seasons were associated with the flu and infection had been suggested as a mechanism triggering stroke.

Improved home heating was one way of reducing the risk of stroke as was the prevention and treatment of infections. It was also vital that hospital stroke specialists were immediately available to assess stroke patients.

NZ Stroke Foundation chief executive Brian O'Grady said stroke patients had a three-hour "window of opportunity" for treatment to reduce damage and improve outcomes but at the moment few people were treated within that time frame.

A general lack of understanding of stroke, the fact 30 per cent of stroke sufferers did not seek hospital services and emergency services did not treat stroke as a medical emergency contributed to the problem.

The foundation, which released guidelines for the management of stroke at the end of last year, wanted all district health boards to provide organised stroke services and for people admitted to hospital to be managed by staff with expertise in stroke and rehabilitation.