What's the medical reason behind Mona Lisa’s smile?

Yellow skin, receding hairline and a neck swelling point in one direction

She not only has the world’s most enigmatic smile, but the woman who posed for the Mona Lisa may also have suffered from thyroid problems, US researchers have surmised.

The thinning hair, yellow skin and a possible goitre on her neck point to a diagnosis more likely to be clinical hypothyroidism than a previous hypothesis of a lipid disorder and heart disease, they write in the September issue of Mayo Clinic Proceedings.

“We believe the enigma of the Mona Lisa can be resolved by a simple medical diagnosis of a hypothyroidism-related illness that could have been the result of a peripartum thyroiditis accentuated by the living conditions of the Renaissance,” say authors Dr Mandeep Mehra, from Brigham and Women's Hospital in Boston, and Hilary Campbell, of the University of California Santa Barbara.

“A complete lack of eyebrows or other hair