The abundance of most molecules and microbes did not shift in a gradual, chronological fashion. When the scientists looked for clusters of molecules with the largest shifts, they found these transformations tended to occur when people were in their mid-40s and early 60s. The mid-40s aging spike was unexpected and initially assumed to be a result of perimenopausal changes in women skewing results for the whole group. But the data revealed similar shifts were happening in men in their mid-40s, too. “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,” said Dr Xiaotao Shen, a former postdoctoral scholar at Stanford medical school and first author of the study who is now based at Nanyang Technological University Singapore.
The first wave of changes included molecules linked to cardiovascular disease and the ability to metabolize caffeine, alcohol and lipids. The second wave of changes included molecules involved in immune regulation, carbohydrate metabolism and kidney function. Molecules linked to skin and muscle ageing changed at both time points. Previous research suggested that a later spike in aging may occur around the age of 78, but the latest study could not confirm this because the oldest participants were 75. The pattern fits with previous evidence that the risk of many age-related diseases does not increase incrementally, with Alzheimer’s and cardiovascular disease risk showing a steep uptick after 60. It is also possible that some of the changes could be linked to lifestyle or behavioral factors. For instance, the change in alcohol metabolism could result from an uptick in consumption in people’s mid-40s, which can be a stressful period of life. The findings have been published in the journal Nature Aging.
