A large new study suggests that higher levels of a common amino acid called tyrosine may be linked to a shorter lifespan in men.

The research, published recently in the journal Aging, examined whether blood levels of two amino acids, phenylalanine and tyrosine, were connected to how long people live.

Amino acids are building blocks of protein. They are found in protein-rich foods such as milk, eggs and meat, and are also sold as dietary supplements.