What's the meaning of "recognize" in this context?

Question

This is quoted from article Moderate exercise not only treats, but prevents depression:

Physical activity is being increasingly recognized as an effective tool to treat depression. PhD candidate George Mammen’s review published in the October issue of the American Journal of Preventive Medicine has taken the connection one step further, finding that moderate exercise can actually prevent episodes of depression in the long term.

What does recognize said above mean? I've looked up OALD and there are several definitions that could fit this context, but I'm unsure which is the most appropriate, they are:

1. to admit or to be aware that something exists or is true

   SYNONYM acknowledge -They recognized the need to take the problem seriously. -Drugs were not recognized as a problem then. -Nobody recognized how urgent the situation was. -We recognized that the task was not straightforward. -It was recognized that this solution could only be temporary. -Drugs were not recognized to be a problem then.

2. to accept and approve of somebody/something officially

   -recognized qualifications -The UK has refused to recognize the new regime. -He is recognized to be their natural leader.

3. to be thought of as very good or important by people in general

   -The book is now recognized as a classic. -She's a recognized authority on the subject.

Answer 1

I would go with #2, even though all three seems to be good explanations.

Answer 2

The definitions from OALD are all accurate; but you should not take them to be distinct meanings. Think of them rather as shades of meaning that the word can convey in different contexts.

Your context here is a press release from the University of Toronto. It does not usually lie within a university's competence to extend official 'recognition' to scientific facts or hypotheses, so we can pretty confidently exclude definition 2.

Definitions 1 and 3 are actually so similar that I am hesitant to distinguish them, at least in the terms OALD employs. Certainly definition 3 is drawn more narrowly than I would like, for it is just as possible to recognize something as “very bad or trivial” as it is to recognize something as ”very good or important”. I would instead draw distinctions between three uses:

1. recognize NP = acknowledge the existence of NP
   They recognized the need to take the problem seriously = they acknowledged that there was a need to take the problem seriously.

2. recognize NP as COMPLEMENT = acknowledge that NP is COMPLEMENT
   They recognized the problem as worthy of serious concern = They acknowledged that the problem was worthy of serious concern.

3. recognize [that] CLAUSE = acknowledge that CLAUSE is true
   They recognized that the problem needed to be taken seriously = They acknowledged the truth of the proposition that the problem needed to be taken seriously.

As you see, the three uses amount to pretty much the same thing; only the syntactical relationships change. In your example, the syntax is that of my Use 2. What I think the University means is something like:

It is generally acknowledged in the medical profession that exercise may be an effective treatment for depression. PhD candidate George Mammen’s review [...] has taken the connection [between exercise and depression] one step further, finding that moderate exercise can actually prevent episodes of depression in the long term.