A common amino acid linked to focus and brain function may have a surprising downside: higher tyrosine levels were associated with shorter lifespans in men. Credit: Shutterstock A common amino acid found in protein rich foods and many brain health supplements may have an unexpected connection to longevity, according to new research. Scientists reporting in the journal Aging-US examined whether two amino acids, phenylalanine and tyrosine, could influence how long people live (lifespan). Their