According to academics at the University of Toronto, an in-depth analysis of Christie's novels suggests that she was suffering from Alzheimer's disease, The Daily Express reported.
To reach the probable conclusion, researchers studied a selection of Christie's novels written between the ages of 28 and 82, counting the numbers of different words, indefinite nouns and phrases used in each.
They found a 15 to 30 per cent decline in her vocabulary in her last novels, and a marked increase in repetitions.
These could be signs that the Poirot author, who died aged 85 in 1976, had Alzheimer's, said researchers.
"This adds to a trend in textual analysis of prolific public figures who may have had dementia," added Rebecca Wood, of the Alzheimer's Research Trust.
"Even those who lead intellectually stimulating lives can get dementia," Wood added.