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A new study suggests that inhaling secondhand smoke may raise the chances of severe dementia in people. Passive smoking, also known as environmental tobacco smoke (ETS), is already known to cause serious cardiovascular and respiratory diseases, along with coronary heart disease and lung cancer.

But then, due to lack of research, it was not known until now if it also increases the risk of dementia, even though certain studies previously have associated ETS and cognitive impairment.

The study was conducted together by scientists at King's College London and Anhui Medical University, China, along with colleagues in the UK and USA.

The WHO reports that about 80 percent of smokers worldwide live in low- and middle-income countries. Apparently in such countries, the rates of illness and death due to tobacco are the highest.

According to the report, China is the biggest consumer of tobacco in the world, with 350 million smokers.

From the year 2006, various efforts have been taken by the Chinese government to promote smoke-free environments in hospitals, schools, on public transport and in other public places.

However, in spite of such efforts, the recent data still shows a high prevalence of passive smoking in the country, with more than 50 percent people being exposed to secondhand smoke every day.

Also, China has the highest number of patients suffering from dementia in the world, with an increasing number of new cases.

For their study, Dr. Ruoling Chen, senior lecturer in public health from King's College London, and his team quizzed 5,921 subjects aged 60 and above to characterize their levels of ETS exposure, smoking habits and assess levels of dementia syndromes, Medical Xpress reported.

The findings of the study revealed that while 10 percent of the participants had severe dementia syndromes, this had a strong and significant link to the duration of exposure to secondhand smoke.

The associations with severe syndromes were found in people who had never smoked and in former and current smokers, the report said.

"Passive smoking should be considered an important risk factor for severe dementia syndromes, as this study in China shows. Avoiding exposure to ETS may reduce the risk of severe dementia syndromes. China, along with many other countries, now has a significantly ageing population, so dementia has a significant impact not only on the patients but on their families and carers. It's a huge burden on society," Dr. Chen, also a visiting professor at Anhui Medical University, said.

The findings of this study, along with the new recent study by the same scientists, urge for stronger public health measures to protect people from exposure to passive smoking.

"At present, we know that about 90 percent of the world's population live in countries without smoke-free public areas. More campaigns against tobacco exposure in the general population will help decrease the risk of severe dementia syndromes and reduce the dementia epidemic worldwide."

"The increased risk of severe dementia syndromes in those exposed to passive smoking is similar to increased risk of coronary heart disease - suggesting that urgent preventive measures should be taken, not just in China but many other countries," he added.

The study was published in Occupational and Environmental Medicine.