Answer:
D. Gastrointestinal issues or hair loss may occur in those who overdose on vitamin supplements.
Step-by-step explanation:
In this passage, the author develops an argument that supports the idea that vitamin supplements are not only useless, but can even be harmful to your health. Option D shows that these pills can cause some unwanted and harmful effects, such as gastrointestinal issues and hair loss. Option A shows that vitamins are not effective, but it does not show that they are harmful. Option B asks a question, but it does not provide evidence. Option C describes lung cancer, but this effect is caused by smoking, so it is not a direct consequence of vitamin supplements (they only increase the risk).