Like ... food? This is an amino acid, the building block of protein. Many amino acids have pronounced effect in the body or when lacking.

Our bodies are fine-tuned to be somewhat fault-tolerant, but evolution is extraordinarily slow. If our diets diverge over a few hundred years, there haven't been nearly enough evolutionary cycles to compensate for whatever effect that has; particularly if it's minor annoyances like getting jittery with coffee, which was consumed far less as far back as a few hundred years ago.