The language of the diabetes pages of the NHS Direct Online site can only be understood by people whose reading ability is well beyond that of the average UK citizen, the survey says. It warns of potential 'serious consequences' of patients misunderstanding the information.
Dr Maged Boulos, of the University of Bath's School for Health, looked at pages about diabetes on 15 internet health sites run mainly by charities and official bodies.
He found that people would need the reading ability of an educated person aged between 11 and 16.8 years old to understand the sites. However the average reading age of UK citizens is only that of the average educated nine year old.
The hardest of the 15 sites to understand was the NHS Direct Online site, needing a reading age of an educated person aged 16.8 years old, but other difficult sites were NetDoctor.co.uk (15.2 years old), the Juvenile Diabetes Research Foundation, UK (15.8) and the British Diabetic Association (14.9).
Sites with a readability score that was close to the reading ability of the average Briton were NHS Prodigy, University College London Hospitals NHS Trust and BestTreatments.
"Sizeable proportions of Western populations have limited language and math skills making it difficult for them to fully and safely understand and act upon online health information," says Dr Boulos in the study.
He said the study showed that the "readability levels, even for the most readable pages in our study, are well above the estimated reading age of the UK population in general (nine years).
"Public and patient health information that is difficult to understand or liable to misunderstanding by the lay consumer could result in serious consequences.
"Much of the currently available online consumer information on diabetes mellitus (of British provenance) needs considerable re-writing to match the general reading level of the UK population."
He recommends that health providers consider other means of getting health information to the public, such as face-to-face education and videos.
The study used the generally accepted Flesch Reading Ease and Flesch-Kincaid Grade Level formulae to test the readability of documents.
Diabetes mellitus is an important public health condition in the UK and elsewhere, accounting for five per cent of the English NHS costs.
Dr Boulos was the author of a recent study which showed that the NHS needed to hire 5,200 more dentists to bring its dental services up to the standard of other Western countries.
Dr Boulos' paper on the 15 websites will be presented on September 16 to the 2nd HDL 2004: Workshop on Digital Libraries in Healthcare, held at the University of Bath. His full paper can be seen online at:
http://staff.bath.ac.uk/mpsmnkb/MNKBoulos_HDL04.PDF