Middle aged people whose mothers smoked heavily may be at significantly increased risk for breathing problems according to a new study from Australia.

Based on 50 years of follow-up, researchers found that adults exposed as children to their mother's smoking were nearly three times more likely than those not exposed to have chronic obstructive pulmonary disease (COPD).

"Our findings suggest that mothers smoking might be linked to reduced lung function in middle age offspring by influencing lung growth during childhood," said lead author Jennifer Perret of the Allergy and Lung Health Unit, Centre for Epidemiology and Biostatistics, The University of Melbourne.

"A reduction in lung function potential may predispose to lesser lung function in adulthood," Perret told Reuters Health by email.

Current public health messages recommend that no one smokes, especially pregnant women and young mothers, she said.

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The researchers used a long-term health study from Tasmania that began in 1968 with more than 8,000 seven-year-old subjects. The children had lung function tests, along with other health assessments, and their parents answered survey questions including about their own smoking habits.

In 1968, almost 40 percent of mothers and almost 60 percent of fathers were current smokers. One-third of smoking fathers and 17 percent of smoking mothers were heavy users, smoking more than 20 cigarettes per day. Twelve percent of kids were exposed to smoke from at least 40 cigarettes per day including maternal and paternal smoking.

In 2004, more than 5,500 of the original subjects responded to a follow-up postal survey and more than 1,000 underwent additional lung function testing between 2006 and 2008.

About 9 percent of the middle-aged participants who returned for testing had airflow obstruction, according to lung tests.

There was no link between mothers who smoked less than 20 cigarettes daily in 1968 and lung function in their middle aged children, nor was there a link to fathers who smoked any amount. But those with mothers who had smoked more than 20 cigarettes a day had 2.7 times the risk of airflow obstruction in middle age compared to those not exposed, according to the results published in Respirology.

Men seemed more vulnerable than women, and those with heavy-smoking mothers had 3.9 times the risk of COPD as those without the maternal smoking exposure. For women the maternal heavy smoking was linked to a doubled risk.

An individual's personal smoking history was not linked to additional COPD risk from maternal smoking. But another measure of lung function, the efficiency of oxygen transfer to the blood, was significantly more impaired in smokers with maternal heavy smoking exposure compared to smokers without the maternal exposure.

"We know that smoking during pregnancy results in smaller lungs in the babies and we know that maximally achieved lung function (typically at age 25) is lower if parents smoked," said Dr. Jorgen Vestbo, a professor of respiratory medicine at Manchester University in the U.K.

"However, this study has followed subjects for a very long time and can therefore show that in addition to affecting growth, the parental smoking also leads to actual lung disease later in life," said Vestbo, who was not involved in the study.

In general, all passive smoking, whether during pregnancy or early childhood, is bad for children, Vestbo told Reuters Health by email.

Lungs continue to grow for a few years after birth, the number of alveoli, or terminal lung sacs, increases and smoking exposure limits this growth, he said.

"In addition, secondhand smoke exposure leads to irritation and inflammation in the airways and if this becomes chronic there will be scarring (deposition of connective tissue) in the walls of the airways making them smaller and stiffer," he said. In COPD, airflow is limited due to airway inflammation or emphysema.

"(COPD) is the fourth most common cause of death in the world, causing 2.3 million deaths globally," Vestbo said. "Most patients do not die of COPD but of heart disease and cancer like most others," but the lung condition is disabling and impacts many areas of life, he said.