A four-year analysis of a lock of Ludwig van Beethoven's hair suggests lead poisoning could be the cause of certain ailments suffered by the famous composer.

Researchers at Chicago's Health Research Institute have found a concentration of lead 100 times the level normally found in people today in the hair, which was snipped after Beethoven died in 1827 at age 56.

Beethoven suffered from illnesses since his early 20s and eventually became deaf.

Though the researchers aren't sure whether lead poisoning caused his deafness, they do think it may have been responsible for his strange behaviour.

Beethoven was known for having dramatic mood swings, given to towering rages and walking the streets of Vienna humming off key while scribbling in a notebook.

The Health Research Institute scientists still aren't sure about the source of the lead, though one possibility is the mineral water he swam in and drank while staying at spas.

The researchers based their conclusions on chemical analysis by the McCrone Research Institute in Chicago and images taken at the Argonne National Laboratory in Illinois using an electron accelerator that creates the most-detailed X-rays available today.