Final answer:
Grapefruit is a concern for a negative drug-nutrient interaction in Mrs. Z's diet because it can interact with Lipitor, potentially leading to serious side effects such as increased risk of stroke, heart attack, and blood clots.
Step-by-step explanation:
Considering Mrs. Z is taking Allegra and Lipitor, the element of her diet that is a concern for a negative drug-nutrient interaction is d. grapefruit. Grapefruit and grapefruit juice can interact with Lipitor (atorvastatin), potentially increasing the levels of the medication in the blood, which can lead to an increased risk of serious side effects. These side effects may include an increased risk of stroke or heart attack, blood clots, and other conditions such as gall bladder disease or depression. It is crucial for patients on Lipitor to consult with their healthcare providers for personalized dietary advice to avoid such interactions.