PEOPLE with Alzheimer’s disease are less likely to develop cancer – and those with cancer may be protected against Alzheimer’s, new research suggests.

The reason for the link, reported online in the journal Neurology, remains a mystery.

Researchers watched the progress of more than 3,000 people aged 65 and older for several years to see if they developed Alzheimer’s or cancer.

At the start of the study, 164 participants – 5.4% of the total – already had Alzheimer’s disease and 522 (17.3%) were already diagnosed with cancer.

During the investigation, 478 people developed dementia and 376 showed signs of invasive cancer.

However, those who had Alzheimer’s at the start of the study were 69% less likely to become hospitalised with cancer than those who did not.

For Caucasian participants who had cancer when the study started, their risk of developing Alzheimer’s was 43% less than that of those who were cancer-free.

Study leader Dr Catherine Roe, from Washington University School of Medicine in St Louis, US, said: “Discovering the links between these two conditions may help us better understand both diseases and open up avenues for possible treatments.”

Professor Clive Ballard, director of research at the Alzheimer’s Society, said: “This study has provided the potentially interesting observation that Alzheimer’s disease could protect against cancer and cancer against Alzheimer’s disease.

“However, the existence of one of these diseases could mask the symptoms of the other and affect diagnosis. More research is needed to establish categorically if this link exists.”