Humans age significantly at two points in their lives.
Ageing happens at two points in a person's life
A new study questions the long-held belief that getting older is a gradual process after analysis revealed that two major changes occurred at the ages of 44 and 60 respectively.
The study tracked thousands of molecules in people aged between 25 and 75 and could explain why specific health issues - such as musculoskeletal problems and cardiovascular disease - happen at certain ages.
The ageing spike in the mid-40s was initially suspected to be related to perimenopausal changes in the female body but the boffins were shocked to spot the same patterns happening in men.
Professor Michael Snyder, senior author of the study at Stanford University, said: "We're not just changing gradually over time. There are some really dramatic changes.
"It turns out the mid-40s is a time of dramatic change, as is the early 60s - and that's true no matter what class of molecules you look at."