statement about least significant bits in the next field of a linked list in c

statement about least significant bits in the next field of a linked list
in c

I found the following statement about the least significant bits in the
next field of a linked list in c.
"In C, the next field is a pointer. For performance reason related to
memory subsystem on a processor, memory is allocated on word boundaries,
and (at least) two least significant bits in the next pointers are 0."
Is this true? I can't understand why so if so. Please help.