PT56.S3.Q20 - newspaper article about vitamin c

Peter

http://7sage.com/lsat_explanations/lsat-56-section-3-question-20/
The argument first states a general claim about people taking Vitamin C is, on average, healthier and then proceeds to show how he arrived at that conclusion by citing a study about heart disease. I picked (B) over the correct answer (D) without hesitation. The question stem asks "which one of the following, if true, would most weaken the argument in the newspaper article?"

I felt (D), the claim that Vitamin C supplements tend to reduce one's resistance to certain common infectious diseases weakens the conclusion but does not weaken the argument---one that derives the benefits of Vitamin C from the fact that studies have shown it lowers the risk of heart disease.

While (B) isn't an ideal answer, I felt it fit more because it weakens the argument rather than the premise or the conclusion by implying that Vitamin C may not be responsible for the reduction in the risk of heart disease. Furthermore, the question stem asks for "most weaken" rather than "which of the following would weaken" which I read as the answer does not necessarily have to fit perfectly but only needs to be slightly better than the best alternative.

Could someone explain why (D) would be superior to (B) given the question stem?

Thanks!

Alina Artunian

(B) doesn't do anything to the actual argument. It tells us that there are also other things that reduce the risk of heart disease, but that doesn't really affect the argument that people who take vitamin C are healthier than average. It's kind of like if someone says "drinking coffee makes you smarter", answer choice (B) says "exercise also makes you smarter". But that doesn't actually break the link between drinking coffee and making you smarter. Same thing here: (B) just introduces another thing that also reduces the risk of heart disease, but it doesn't attempt to break or weaken the causal link between consuming vitamin C and decreasing the risk of heart disease.
The conclusion here is that "people who take Vitamin C supplements tend to be healthier than average." What (D) does is say, essentially, that just this link between vitamin c and reducing heart disease isn't enough evidence for the conclusion, because these people who "regularly consume high doses of vitamin C", although maybe decreasing their risk of heart disease, are also reducing their resistance to common infectious diseases (which is a bad thing, you want to have high resistance to diseases!). So knowing that high doses of vitamin C can decrease the risk of heart disease, but it also reduces the strength of the immune system, we can no longer conclude that people who take vitamin c supplements tend to be healthier. What if their risk of heart disease is super super low, but they just keep getting the flu? Can we really say they're healthier than average? We just don't know! So that's why (D) weakens it.
I hope that helped!

Peter

I see my error now. Thanks!