Lithium has long been used in the treatment of people living with bipolar disorder and animal studies have found potential neurological benefits. For the first time, scientists from the University of Copenhagen studied naturally occurring lithium’s impact on human health.

In the study, the researchers cross-referenced levels of lithium in the water supply of 151 different waterworks in Denmark against the number of people living with dementia in the healthy population. The results showed that those drinking the tap water with the highest levels, above 15 micrograms per litre, were 17% less likely to have dementia.

However, people whose tap water lay within the mid-range, 5.1 to 10 micrograms, were found to have an elevated risk – being found to be 22% more likely to have dementia. Both the mid- and high-levels were measured against a base level of two to five micrograms in the water.

The study has drawn wide-interest from those involved in dementia research, as lithium is easy to source and would make for a cheap, quick to produce medicine.

Dr James Pickett, Head of Research at Alzheimer’s Society said:  "Lithium triggers a number of useful responses in brain cells that means, theoretically, it might work as a treatment for Alzheimer’s disease. However, despite some success in animals, there hasn’t been enough positive research of lithium in people with dementia to yet convince us that it works.

"This large, well conducted study explores the potential of lithium in drinking water to prevent, rather than treat, dementia by looking at how cases of dementia vary with natural changes in lithium exposure across Denmark. Although people exposed to the highest levels of lithium appear to be slightly protected, those exposed to intermediate levels had higher rates of dementia than those with the lowest levels of lithium in their water."

The ‘sweet spot’ of having levels neither too low nor too high could well be the biggest issue with using lithium for treatment, both in trials and potentially in larger population groups. Many reports based on the study suggested upping levels of lithium in the water supply but individuals react to levels of the naturally occurring mineral very differently. This could also go some way to explain why mid-levels of lithium were found not to be protective.

The main result of the study may be to generate further interest into studying the impact of lithium on those with neurodegenerative disorders.