The role of って in 「コーヒーって若いうち**は**あまり飲まないほうがいいんですか。」

Question

Consider

コーヒーって若いうちはあまり飲まないほうがいいんですか。

Is it best to not drink a lot of coffee while you're young?

Here, is って just short for と言う, and it acting as a topic marker (は)? If so, would the sentence change in meaning (or connotation) if って was just replaced with an additional は (making there be two は's in the sentence)?

Answer 1

って has various usages, and this って is short for no particular word. This one is a topic marker that is more emphatic than は.

Generally speaking, it's okay to have more than one は in one clause when a contrastive-wa is involved. According to this answer, "There can be only one thematic は in a sentence. If you see a second one, the second is certainly contrastive, and the first might be".

• 彼は背が高い。
  He is tall.
• 彼は背は高い。
  He is tall (at least, although he lacks something).

However, your sentence does not have two は strictly, and the following sentences sound almost the same to me.

• 彼女って両親が政治家なんだよ。
  彼女って両親は政治家なんだよ。
  As for her, her parents are politicians.
  ^{(No contrastive-wa is involved)}

So grammatically speaking, I think って is not necessarily a precise replacement of は. Sometimes って is just an expression to give a broader topic, and it doesn't necessarily stop the existence of a proper thematic は.

Answer 2

The って is a topic marker, but not a replacement for は. It is rather a choice between は and って, the latter of which is better due to the lack of repetition when it is possible to use って at all.

1. コーヒーって若いうちはあまり飲まないほうがいいんですか。
2. コーヒーは若いうちはあまり飲まないほうがいいんですか。

are both ok, but 1 is more commonly used. Double は is possible, but my impression is that it tends to be avoided if possible.

On the other hand

3. コーヒーって若いうちはあまり飲まないほうがいい

is odd if not completely unacceptable. In this case, コーヒーは若いうちは... is definitely better. Some sort of ending would be required to make it natural.

4. コーヒーって若いうちはあまり飲まないほうがいい{らしいよ, ですよね}

Both versions of 4 would be better to me than コーヒーは-equivalent.