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。」


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)?




って has [various
usages](https://dictionary.goo.ne.jp/word/%E3%81%A3%E3%81%A6/#jn-147762), 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](https://japanese.stackexchange.com/a/51/5010), "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.

