Medical experts have also pointed to her yellowed skin and what could be a goiter – which would appear as an enlargement in the neck – as symptoms of various conditions.
According to Mandeep R. Mehra, MD, medical director of the Heart & Vascular Center at Brigham and Women's Hospital, hypothyroidism could explain these traits.
Hypothyroidism, in which the thyroid gland does not produce high enough amounts of key hormones, can cause thinning hair, yellow skin, and goiters.
"The enigma of the Mona Lisa can be resolved by a simple medical diagnosis of a hypothryroidism-related illness," write Mehra and Hilary Campbell of the University of California Santa Barbara in a WHERE Letter to the Editor, published in the Mayo Clinic Proceedings journal.
"In many ways, it is the allure of the imperfections of disease that give this masterpiece its mysterious reality and charm."
While previous analyses have suggested other conditions may have been at play, Mehra says a heart disease and lipid disorder would be unlikely, considering she lived to the age of 63.
With these disorders, she likely would have died much younger given the medical limitations of the 16th century.
A recent pregnancy before the portrait was painted could have given rise to peripartum thyroiditis, Mehra says – or the inflammation of the thyroid after pregnancy.
Gherardini is known to have given birth not long before the painting was commissioned.
Diet in Italy during this time is also known to have lacked iodine, which could explain the goiter, or swollen thyroid.
"It is possible that she suffered from a subclinical presentation of peripartum thyroiditis, with an early manifestation of hyperthyroidism eventually setting into a chronic phase of hypothyroidism," the researchers write.
"This, coupled with the living conditions and iodine-deficient diet of this period in the Florentine region, would have characteristically led to the secondary manifestations of underlying hypothyroidism."
