Exposure to cigarette smoke can increase your chances of being diagnosed with dementia, says a new study from China.

Secondhand smoke contains more than 50 substances that can cause cancer, according to Medline Plus. Passive smoking can cause lung cancer, nasal sinus cancer, respiratory tract infections and heart disease. Although, passive smoking is considered a risk factor for dementia, studies backing up the idea were lacking.

Only 11 percent of the world's population is protected by smoke-free laws, according to a news release from King's College.

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

The data for the study came from 5,921 people aged over 60 in the rural and urban communities of Anhui, Guangdong, Heilongjiang, Shanghai and Shanxi. Researchers assessed peoples' exposure to smoke, their smoking habits and symptoms of dementia.

Dementia isn't a specific disease but is a term that describes loss of brain function that can occur due to many reasons. Dementia generally occurs after 60 years of age and is characterized by loss of memory, language, thinking and behavioral changes.

Study analysis showed that some 10 percent of the study group was suffering from severe dementia syndromes and this was associated with their exposure to smoke, either current, former or passive smoke.

"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," said author of the study Dr Ruoling Chen.

"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," Chen added.