There have been a lot of theories about the Mona Lisa over the years: about who she is, why she doesn't have eyebrows, and, most pressingly, why she's smiling.

A researcher in Palermo, Italy, has a new idea: that Leonardo's "La Gioconda" owes her facial expression to her health conditions. Vito Franco of the University of Palermo believes that the portrait's enigmatic subject suffered from xanthelasma, a subcutaneous accumulation of cholesterol, in the hollow of her left eye. The condition suggests a very high level of cholesterol.

Franco has a history of spotting medical conditions in Renaissance paintings. He's previously diagnosed the genetic bone-tissue disorder Marfan syndrome in the subjects for Botticelli's Portrait of a Youth and Parmigianino's Madonna with Long Neck. Michelangelo's appearance in Raphael's The School of Athens suggests "an excess of uric acid, typical of those afflicted by renal calculosis," that Franco speculates could be a result of living off of bread and wine while working on the Sistine Chapel.

Read more at the Telegraph.