Hong Kong’s hazy days may have more deadly effect on those with mental illnesses, researchers find
People with conditions such as dementia, bipolar disorder and depression were 16.4 per cent more likely to die on the first day of hazy weather compared to a normal day with a clear sky, university study finds
Hazy days are more likely to trigger fatal incidents among those with mental health issues such as dementia, bipolar disorder and depression, according to the first study in Hong Kong trying to establish a link.
For those with chronic diseases, it is well known that air pollution worsens their condition, but according to the study by Hong Kong Polytechnic University, which is looking at the relationship between hazy days and the mortality details of the deceased, those with mental problems were 16.4 to 26.5 per cent more likely to die on a day with severe air pollution.
Hong Kong is frequently covered in a thick blanket of smog owing to the air pollution, which contributes to reduced visibility.
Other than a psychological impact, a cold hazy day also posed physical harm to patients with heart and respiratory diseases, increasing their risk of death by up to 17 per cent, the study found.
“People usually feel very depressed and stressed on a gloomy day when compared with a bright, sunny day,” said one researcher, assistant professor Yang Lin of PolyU’s School of Nursing.
“Bad weather is likely to put more psychological stress on the population and trigger an acute situation.”
A total of 111 hazy days were recorded by the Hong Kong Observatory in the city between 2007 and 2014. It defines a hazy day as one when the visibility is reduced to below 5,000 metres by suspended particulates in an atmosphere with a relative humidity of 80 per cent or below.
On the hazy days, a total of 11,365 people died, according to the study. Researchers then obtained the causes of death and developed a model to calculate the implicated health risk.
It was found that people with mental health conditions, such as dementia, bipolar disorder and depression, were 16.4 per cent more likely to die on the first day of the hazy weather, increasing to 26.5 per cent on the second day, compared to a normal day with a clear sky.
Those with heart or respiratory problems were 11.8 per cent more likely to die on day one and 16.7 per cent more likely on day two.
Other reasons of death related to the nervous system and skin problems were found to be less relevant to air pollution.
“The additional effects contributed by the urban environment on the mortality associated with mental and behavioural disorders can be more extreme during specific hazy events,” the study said.
Psychiatrist John Wong Yee-him, who was not involved in the study, pointed out that while Hong Kong had no precedent study on how hazy weather affected people with mental health conditions, researchers in Britain called this seasonal affective disorder.
It is also called “winter depression” as the effect on mood and energy levels are more apparent and tend to be more severe during the British winter due to the shorter days.
Yang said that while it would require further research on how air pollution damages the brain physically, the study indicated that the urban environment can further undermine mental health.
It could also result in an excessive increase in mental-related mortality in specific neighbourhoods.
More community support should be given to mental health patients in areas with lower environmental quality – where there was less vegetation, higher anthropogenic heat and higher concentration of harmful particulates PM2.5.
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Cold hazy days should also be targeted, with more care on cardiorespiratory issues for the population in all areas.
“Based on our study, better guidelines for disaster risk management and health warning system development should be implemented,” said co-author Derrick Ho Hung-chak, a research fellow in the university’s land surveying and geo-informatics department.
“Public health surveillance should be developed in advance to reduce the natural hazard risk to the urban population.”
The paper was published in science journal Environment Internationalin December.