What is the story?
Eating large amounts of cured meats such as bacon and ham can cause lung damage, according to media reports.
US scientists have found that people who ate cured meats at least 14 times a month were twice as likely to have COPD as those who consumed none.
High levels of nitrites in the meat may be to blame, say the papers. Nitrites are used in cured meats as preservatives and to preserve colour.
But it seems that nitrites may cause structural changes to the lungs resembling emphysema.
COPD is typically associated with smoking. It is the UK's fifth biggest killer, claiming around 30,000 lives a year.
What is the research?
The findings come from a study of 7,352 adults aged 45 or older participating in the Third National Health and Nutrition Examination Survey.
The research has been published in the latest issue of the American Journal of Respiratory Critical Care Medicine, but was first presented last September at the annual congress of the European Respiratory Society in Munich.
For the analysis, food frequency questionnaires were studied and participants were separated into five groups depending on their monthly consumption of cured meats. Participants were also assessed using spirometry.
This showed people who ate 14 or more portions of cured meat had forced expiratory volume in one second (FEV1) 110ml smaller than those who ate no cured meat.
Forced vital capacity (FVC) was unaffected by how much cured meat a person consumed.
COPD was defined as FEV1/FVC of 0.7 or less and an FEV1 less that 80 per cent of that predicted.
The odds ratio for developing COPD was 1.93 in those who ate cured meat 14 or more times a month compared with those who ate none.
People who ate cured meats were also more likely to smoke, be from a low socio-economic background and eat less fish, fruit and vegetables. Adjustment for all confounding factors reduced the odds ratio to 1.78.
What do researchers say?
Lead researcher Dr Rui Jiang, from Columbia University Medical Centre in New York, blamed high levels of nitrites in cured meats for the increased risk of COPD.
'Cured meats such as bacon, sausage and cured hams are high in nitrites, which are added to meat products as a preservative, an anti-microbial agent and a colour fixative,' he said.
'Nitrites generate reactive nitrogen species that may cause damage to the lungs, producing structural changes resembling emphysema.'
As the increased risk of COPD with cured meat intake remained when confounding factors were considered, Dr Jiang said ‘the association between cured meats and lung function was unlikely to be explained by potential dietary confounding factors reported in previous studies'.
What do the experts say?
David Price, professor of respiratory medicine at Aberdeen University and member of General Practice Airways Group, said: 'This is an interesting association but I would like to see it replicated in another dataset.'
A spokesman for the Food Standards Agency said last July that the European Food Standards Association put restrictions on how much nitrite could be included in cured meats.
But this was not done over fears of a link between nitrites and COPD.
Professor Peter Calverly, of the British Thoracic Society, said: 'This study illustrates that factors other than smoking may contribute to COPD.
'Although smoking remains the single most significant cause of COPD this research seems to suggest other factors may result in increased risk of the disease.'
Dr Keith Prowse, chairman of the British Lung Foundation, said: ‘This is a large study providing some interesting results.
'We will be looking very carefully at it to see if it provides any pointers to the cause of COPD. We urgently need more research into this hugely disabling disease.'
Am J Resp Crit Care Med 2007; 175: 798-804