We understand from the passage that ----.

Sarah blamed middle age for her forgetfulness and
for the way she kept losing her train of thought. She
mentioned this to her doctor, who promptly ordered
lab tests to check for a possible medical cause, and
then found one: Sarah was deficient in vitamin B12.
While people associate this problem with strict
vegetarianism (meat and dairy are the main sources
for the vitamin), Sarah had a different condition: she
had developed antibodies against a stomach
chemical that is needed to absorb B12. After being
given daily megadoses of B12 for three months,
Sarah is happy to report that her memory is back to
normal.