What is Dr. Kureha's secret?


In the Drum Island arc, Dr. Kureha always asks this:

!["You want to know the secret of my
youthfulness?"](https://i.stack.imgur.com/65HPb.jpg)

So, what is the secret of her youthfulness? Is it because of her medicine? Her
lifestyle? Maybe she found a fountain of youth?




She being a doctor, must have found some medicine which she drinks from her
beer bottle. Also she was the first one to mention the will of D and she knows
the actual name of Gol D Roger, shows that she actually must be around 140
years of age.

