Asthma rates in adults have soared in the last 20 years, according to research carried out in Scotland.

And it is not simply better methods of diagnosing asthma that are responsible for the rising numbers, although more public awareness of the symptom may have contributed, they conclude.

According to records taken between 1972 and 1976, approximately 3.0% of adults had asthma, and 5.8% had hayfever.

In 1995, asthma had increased to 8.2%, and hayfever to almost 20%.

Measurements of asthma in children have already shown a similar increase over the last few decades.

Smokers hit as well

Although many people "grow out" of asthma, a corresponding rise in adults was expected.

But scientists still do not know why asthma rates are rising at such a sharp rate.

This is the first UK study to look at 20-year increases in asthma prevalence - most studies of 1970s data focus on bronchitis and other lung disorders.

All the volunteers for the adult study live in Renfrew and Paisley in west Scotland, and were aged between 45 and 54.

Asthma rates among smokers also increased along the same lines.

In 1972-6, 1.6% of smokers had asthma, while in 1995, this had increased to 5.3%.

Dr Martyn Partridge, chief medical adviser to the National Asthma Campaign, said: "This study confirms that, for some people with asthma, diagnosis is more accurate now than 20 years ago.

"But overall, the study also confirms the significant increase in the number of people suffering from asthma over the last two to three decades."

The research was published in the British Medical Journal.