The world's 94 790 nuns "pay a terrible price for their chastity" because of the increased risk of breast, ovarian and uterine cancers among women who do not get pregnant, have children and breastfeed, they said.
Roger Short, a reproductive biologist at Melbourne University, said it was incumbent on the pope not just to permit nuns to take the pill but be out there lobbying for them to do so.
"He should say something to see that something gets done," the professor said. "It would be expensive for any nunnery to get the pills, and the Catholic Church should be paying for that."
Short and cancer researcher Kara Britt from Monash University in Melbourne recently published a paper in the medical journal The Lancet detailing the extra cancer risk that nuns have borne through the ages.
The first reference to their higher mortality came in 1713 from Italian physician Bernadino Ramazzini.
Because nuns do not get pregnant, bear children or breastfeed, they have far more periods over their lifetimes and forego a certain level of protection from breast, ovarian and uterine cancer compared with other women.
Short accepted that the church does not ban the use of the pill for non-contraceptive purposes, but argued that it does not give the encouragement it could.
"I've never met a Catholic priest who has thought that there are health benefits to taking the pill," Short said.
In response, Father Brian Lucas, general secretary of the Australian Catholic Bishops Conference, said there was no real need to go from permitting the pill's use to encouraging it.
"That's a false distinction," Lucas said. It was more important to distinguish "between whether it's being used for contraceptive purposes or it's for medical purposes", he said.
Lucas also noted that there were downside health risks from contraceptive pill, such as blood clots. "These are medical issues, not moral issues," he said.