By MARTIN JOHNSTON



Synthetic duvets - long recommended to help asthma sufferers - can make the condition worse, says research published today.



Quilts with man-made fillings, by far the most common type used in New Zealand, contain 15 times more of a kind of bed dust that causes allergic reactions than feather duvets, the study found.



It has prompted an asthma advisory body to stop advocating the use of synthetic pillows and duvets instead of feather bedding.

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New Zealand has one of the highest rates of asthma in the world.



One in six people has the disease and it is the most common cause of hospital admissions for children.



Asthma sufferers are entering hospital at more than double the rate of 30 years ago.



The Wellington School of Medicine study, the first to look specifically at duvets, builds on work by the same research group implicating synthetic bedding in the development of asthma.



Overseas studies linking asthma severity to bedding have used composite samples of bedding dust.



Synthetic duvets are much cheaper and far more popular than feather/down ones.



The Warehouse said 78 per cent of the duvets it sold were synthetic, 15 per cent were feather/down and 7 per cent were wool.



At $69.90, the retail chain's cheapest single feather duvet inner is more than four times dearer than its lowest-priced synthetic equivalent ($14.99).



In the latest study, the researchers analysed bed-dust samples vacuumed up at 34 Wellington homes.



They found that synthetic pillows contained about seven times more of an allergen from house dust mites, called "der p 1", than feather pillows.



Der p 1 is linked to the development of allergic asthma in infants, and in aggravating asthma in people who already suffer from it.



Levels of the allergen were significantly higher in duvets and pillows when under-bedding was used, and on mattresses more than 10 years old.



The study, published in today's New Zealand Medical Journal, says the higher levels in synthetic bedding are probably due to a looser weave in their covering fabrics than in those used for feather duvets and pillows.



This allows the mites to get in and their faeces to spread more easily.



The researchers recommend the use of special, tightly woven covers, which are available from local asthma societies.



The study concludes: "It is at least plausible that the increased use of synthetic bedding materials in New Zealand over the last two decades has added significantly to the allergen burden and thus to the severity of allergic asthma."



One of the study's authors, research scientist Robert Siebers, said yesterday that the present advice - which urged people who were sensitised to the allergen to choose synthetic bedding - might be inappropriate.



In light of the findings, the Asthma and Respiratory Foundation, which saw the research before publication, stopped advocating the use of synthetic pillows and duvets in preference to feather ones.



"Our website was adjusted in December to take account of some of this data," said the foundation's medical director, Professor Ian Town.



The foundation said in February that asthma costs New Zealand $825 million a year - double the previous estimate - in treatment, lost working time, disability and premature death.



The condition causes airways to become inflamed and makes sufferers wheeze and gasp for breath.