Researchers analysed blood samples from 513 middle-aged men attending a medical centre for a routine examination between 1996 and 1998. The samples were then matched to those from 513 men seen in 1981-2 and 513 seen in 1975-6.
All samples were tested for sensitivity to Phadiatop - a standard preparation of 11 common allergens such as grass pollen, pet dander (skin flakes) and house dust mite.
Positive samples were re-tested for levels of specific IgE (an immune system response) to three inhaled allergens grass and tree pollen, and cat dander. The samples were also tested for antibodies to hepatitis A and to H. Pylori infections.
The team found highly significant increases over time in the proportion of men testing positive to Phadiatop and with specific IgE to the three inhaled allergens. The average rate of increase was equivalent to an additional 4.5% of men becoming Phadiatop positive each decade.
There was no tendency for atopy to decline as men grew older. There was also no link between past infections and adult atopy.
These data show that atopy in middle aged men has increased during the last quarter of the 20th century, and that the prevalence of atopy does not decline with increasing age, as previous studies have suggested, say the authors.
The reason for the increase in atopy is unknown, but it is unlikely to be due to either an increased exposure to specific allergens or to declining childhood infections, they conclude.