Data collected through the quality management and analysis system for 2005/6 has shown that while the average prevalence of hypothyroidism is 2.8 per cent, it was diagnosed in 5.4 per cent of people in some areas of Scotland, compared with just 1.6 per cent in some areas of south-east England.
Dr Douglas Fleming, director of the RCGP’s Birmingham Research Unit, said: ‘There is a good scientific basis for the variability of hypothyroidism relating to the iodine content of the water supply in childhood and this could have repercussions in elderly people in whom most thyroid disease is diagnosed.’
Dr Wing May Kong, an expert in endocrinology from Imperial College London, said: ‘In most areas of the UK iodine isn’t a problem.’
This is because the UK is island-based, so most places are close enough to the sea — a main source of iodine. But highland areas are further from the sea, which ‘could explain some of the high prevalence in Scotland,’ said Dr Kong.
Under-diagnosis could also be a factor, she said.
‘Because a lot of mild cases won’t get diagnosed, it will vary according to GP tendency to do thyroid function tests.’
In Glasgow and Tayside, a thyroid register has been set up, improving diagnosis of the condition, said Dr Kong.
This could explain why surrounding areas have such high prevalence rates.
‘Because GPs are involved in that, they may be doing more thyroid tests in the population,’ Dr Kong added.
Age is another important factor in hypothyroid disease. Among over-60s, prevalence can reach 10 per cent in women and up to 6 per cent in men.
In comparison, 0.5–1 per cent of people in their twenties and thirties have hypothyroidism.
The young population of London could partly explain the low prevalence in that area.
However, as hypothyroidism develops slowly, cases may not be diagnosed because of a lack of continuous contact between patient and GP in London.
‘In London people change GPs all the time, so GPs might not pick it up,’ suggested Dr Kong.