Rachel Tompa, writing for Stanford Medicine News Center:

If it’s ever felt like everything in your body is breaking down at once, that might not be your imagination. A new Stanford Medicine study shows that many of our molecules and microorganisms dramatically rise or fall in number during our 40s and 60s.

Researchers assessed many thousands of different molecules in people from age 25 to 75, as well as their microbiomes — the bacteria, viruses and fungi that live inside us and on our skin — and found that the abundance of most molecules and microbes do not shift in a gradual, chronological fashion. Rather, we undergo two periods of rapid change during our life span, averaging around age 44 and age 60.…

“We’re not just changing gradually over time; there are some really dramatic changes,” said 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.

It brings to mind Hemingway’s quote about bankruptcy happening “gradually, then suddenly.” As several friends in their mid- to late-40s have noted, “This explains why everything hurts for me!”