Drinking tap water could put 40 per cent of UK population at greater risk of dementia

It is the first study of its kind

Scientists believe around 40 per cent of the UK population could be at risk of developing dementia as their drinking water may contain low levels of calcium and magnesium.

Those residents who live in a 'softer water' area could be more likely to develop the degenerative disease as these minerals may have a protective effect on the brain.

This is due to the low levels that might cause pipes to corrode faster, therefore allowing toxic elements such as lead into the body.

Soft water is between zero and 60mg of calcium carbonate per litre of water while hard water is defined as between 120 and 300mg/L.

The data found that residents exposed to softer water had a 34 per cent higher risk of vascular dementia compared with those who had a hard water supply.

Low concentrations of calcium were also associated with a 63 per cent higher risk of dementia and a 53 per cent greater risk of MS. Low levels of magnesium were associated with a 25 per cent higher risk of Alzheimer's.

Scotland, Yorkshire, Cornwall and parts of Wales are soft water areas.

The study found residents with soft water had structural changes to their brain in twenty different areas.

The groundbreaking study was carried out by a team of scientists from Imperial College London and China and was based on data from nearly 400,000 people in the UK.

It was one of the first studies to look at the potential impact of tap water's calcium on nuerodegenerative disease.

While some scientists praised the study others have criticised it.

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Dr Emma Anderson, Associate Professor of Epidemiology at King's College London, said: "Overall I think this is a poorly conducted study and not one we should be using to assess whether water hardness should be taken more seriously."

Dr Tom Russ, director of the Alzheimer Scotland Dementia Research Centre, said: "There is more work to be done on any environmental factor that might be linked to dementia, and this shows that water may potentially be a part of that. It's important to recognise that the study doesn't prove that water type contributes to the development of dementia.

"There's still a much bigger risk of dementia from other risk factors such as smoking, high cholesterol and high blood pressure and most people shouldn't be too worried about the effect that tap water might have. If it has any effect, it'll be very small."