It is probably the most important of all classroom tools, so we shouldn't be surprised that teaching carries a high risk of voice disorders. Vocal dysfunction interferes with job satisfaction, performance and attendance; according to the US study, 18.3 per cent of teachers miss at least one day of work each year because of it. The annual cost of absenteeism and treatment related to voice disorders is estimated at about $2.5 billion.
The study, carried out by the otolaryngology department at the University of Utah, Salt Lake City, also suggests that teachers of certain subjects may be more susceptible than others because of the different voice patterns they use. For instance, teachers of special and vocational education, who told researchers they rarely had to shout and usually talked quietly, had the lowest risk. In general, such teachers have smaller classes and more one-to-one interaction with pupils - they spend much of their time supervising rather than instructing.
At the other end of the spectrum, teachers who engage in vocally intense activities - such as loud talking and singing - were at greater risk.
Chronic problems were most common among teachers of vocal music, which suggests that regular singing, more than other vocal activity, disproportionately increases tissue injury.
But the study also found that physical education teachers and coaches were not at greater risk. This could be because they engage in brief, intense periods of shouting or yelling which are not enough to cause serious injury.
Risk factors other than pattern and type of voice use, may also be important. For example, the finding that some science teachers are "high risk" might be explained by their exposure to high-risk materials.
Sixty-nine per cent of chemistry teachers who told the researchers they worked closely with chemicals - many of them corrosive, carcinogenic andor highly toxic - also reported suffering from voice disorders.
Previous research has also found a link between voice disorders and the dimensions of a classroom; the number of disorders grows as the size of a classroom increases. And many classrooms have poor acoustics, so putting stress on teachers' voices. Background noise from heating, ventilation and air conditioning, from outside the building, from other classrooms and from the children in the classroom is also a factor. One way to combat this problem is to invest in amplification systems. A handful of far-sighted British schools are already reaping the benefits of this technology, which means teachers don't have to raise their voices to overcome background noise, thus protecting those vital throat muscles.
Professor Raj Persaud is a consultant psychiatrist at the Maudsley hospital and senior lecturer at the Institute of Psychiatry in London. He is a fellow of University College London, and author of From the Edge of the Couch published by Bantam Press, pound;12.99. Email: firstname.lastname@example.org