I think the average bust size has gone up due to obesity. But according to old medical journals, doctors would come across women around the world with extremely large breasts. One woman in the 1800's they found with breasts around 15 kilograms each, they offered her surgery, but she said she was proud as her role as the village wet nurse.
You still see these cases today if you check modern medical journals. Typically women want them removed because of unwanted attention and quality of life issues.
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