By Maggie Fox, Health and Science Editor

WASHINGTON, Aug 30 (Reuters) - Nearly 2 million older people alive today in China are likely to die from emphysema and other chronic lung diseases caused by second-hand smoke, researchers predicted on Thursday.

Their estimates are part of a series of studies showing that chronic obstructive pulmonary disease, or COPD, is far more common than had been recognized around the world and will present a serious problem for health officials.

COPD includes emphysema, chronic bronchitis and some types of serious chronic asthma. Smoking is by far the leading cause.

Dr. Peymane Adab and K.K. Cheng of Britain's University of Birmingham, with colleagues in Hong Kong and Guangzhou, used data from a study of 20,430 men and women over the age of 50.

Most had never smoked.

"More than half of never smokers reported exposure to passive smoking in their workplace and at home, with 28 percent reporting high levels of total adult exposure," Adab and Cheng wrote in their report, published in the Lancet medical journal.

Anyone who spent more than 40 hours a week in and around cigarette smoke for more than five years was considered to have high exposure.

These people were on average 48 percent more likely to develop COPD, the researchers found.

"Of all deaths in China, around 11.6 percent among never smokers are attributable to COPD," the researchers wrote.

"If our risk estimates are correct, and assuming that current mortality and passive smoking exposure patterns continue, of the 240 million people aged over 50 years alive today in China, high exposure to passive smoking would result in about 1.9 million excess deaths from COPD among never smokers."

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China has high rates of smoking, with an estimated 40 percent of the population being current or former smokers.

The World Health Organization estimates that 2.5 million people die of COPD every year, about as many as die from AIDS.

But these numbers could be low, said Dr. Sonia Buist and colleagues at Oregon Health & Science University.

Their study of 9,425 people aged 40 and over from 12 countries found that more than 10 percent of them had moderate to severe COPD. That is far higher than the most recent estimate of 4.3 percent.

"These results suggest that future anti-smoking policies should, in addition to targeting active smoking, also consider addressing passive smoking," Dr. Ana Menezes and Dr. Pedro Hallal of the Universidade Federal de Pelotas in Brazil wrote in a commentary.

In Buist's survey, Cape Town, South Africa had the most cases of COPD, with 22 percent of men and more than 16 percent of women affected.

Hannover, Germany had the lowest rates, with 8.6 percent of men and 3.7 percent of women affected.

An estimated 10 million Americans have been diagnosed with COPD, but U.S. health survey data suggest that as many as 24 million Americans have the ailment, the Lancet reported.

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