According to research undertaken by Stanford Medicine in the US, ageing is non-linear and there are periods of significant change around the ages of 44 and 60.

The longitudinal study, Nonlinear dynamics of multi-omics profiles during human aging, published in the journal Nature Aging, followed 108 participants aged between 25 and 75 years. Biological samples – blood, stool, skin swab, oral swab and nasal swabs – were taken every three to six months for an average of 1.7 years and a maximum of 6.8 years.

The evidence pointed overwhelmingly to ageing being a non-linear process, with the risk of developing age-related diseases spiking at certain ages – especially after 60.

Only 6.6 per cent of molecules displayed linear changes throughout human ageing, a finding which is consistent with previous research.

“We’re not just changing gradually over time; there are some really dramatic changes,” says Michael Snyder, PhD, professor of genetics and the study’s senior author. “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 in the body.”

At 44 and 60 there are distinct shifts in ageing, including the ability to metabolise caffeine, alcohol and lipids. The ageing of skin and muscle is also markedly accelerated at both of these crests, as is cardiovascular health.

The second wave of changes includes molecules involved in immune regulation, carbohydrate metabolism and kidney function. After 60 there’s a rapid decline in the immune system, as well as oxygen carrier activity and a higher risk of developing both kidney and cardiovascular disease and Type 2 diabetes.

While the ageing spike at 60 was not surprising to the scientists, as this has long been known to be a critical time when ageing accelerates, the changes in the mid-40s were less expected and were initially assigned to the perimenopause, until they found the changes occur in men as well.

“This suggests that while menopause or perimenopause may contribute to the changes observed in women in their mid-40s, there are likely other, more significant factors influencing these changes in both men and women. Identifying these factors should be a priority for future research,” says first author of the study, Xiaotao Shen.

Limitations of the study was the narrow geographical area: participants needed to be close to Stanford University because of the expense of a longitudinal study and the collection of samples. Also it was a modest-sized group and there was no behavioural data, which could explain some of the factors, for example the dysfunction in alcohol metabolism could be the result of increased alcohol consumption during a stressful period in the 40s.

While the team plans to explore these drivers of change further, they emphasise the importance of paying increased attention to health during the 40s and 60s, for example increasing exercise to protect the heart and increase muscle mass and decreasing alcohol consumption.

Snyder says: “I’m a big believer that we should try to adjust our lifestyles while we’re still healthy.”