Sections of DNA that control when women go through the menopause have been identified by scientists.
Their report, in the journal Nature Genetics, identified genes involved in how the body repairs itself.
Ultimately the findings could contribute to a fertility or menopause test, or lead to new drugs.
The Royal College of Obstetricians and Gynaecologists said the results were important for those at risk of an early menopause.
Most women go through the menopause between the ages of 40 and 60. However, what controls that timescale is not completely clear.
Comparing the DNA of nearly 70,000 women allowed the researchers to identify the differences between those starting the menopause early and late.
The team at Exeter and Cambridge universities showed that at least two repair mechanisms were involved.
The first is used when the eggs are being formed and the woman's DNA is being broken, rearranged and repaired.
The second corrects damage, caused by factors such as smoking or alcohol, throughout a woman's life.
Both would influence the number of viable eggs a woman has.
Women become infertile about 10 years before the menopause starts.
So could this knowledge lead to a test that predicts the age of menopause?
Dr Anna Murray, one of the researchers from the University of Exeter, told the BBC News website: "We would love to be able to do that, but the answer is no.
"[But] possibly by adding other risk factors such as smoking, hormone levels we might be able to get towards something more useful."
The age of menopause is thought to be controlled by a 50-50 split between genetics and lifestyle choices.
However, even after discovering 56 genetic variants linked to the age of menopause, that comprises only 6% of the total variation.
Dr Murray said the findings could help develop new drugs: "We really don't understand the process of egg loss, the timing of it, so better understanding of the basic biology of losing eggs will help us with that."
The researchers also found genes that controlled menopause timing were involved in both the age of puberty and the development of breast cancer.
Dr Edward Morris, a spokesman for the Royal College of Obstetricians and Gynaecologists, said: "We have known for some time about the fact that an early menopause protects against breast cancer whilst a late menopause increases the risk.
"It is reassuring that such a large study taking a genetic approach has clearly demonstrated this link.
"In addition this study has shown that there may well be future possibilities not only to have a clearer understanding of the length of a woman's reproductive life, but possibly to find treatments in the future.
"This type of knowledge would be of particular importance in women with a high risk of early menopause."