Thanks for your comment, Berneddi. Yes I've also noticed that 'as' is used more than for. I only wanted to know if it's ok to use 'for' to refer to a cause of something, because I usually  like to use both of them to create variety.

"For" can be used "to refer to a cause of something", but my feeling is that it is getting a bit archaic.

I believe that you might find "as" used more often than "for" for that purpose.

It would be good to see some examples of what you're thinking of, then it'll be clearer for everyone to see. Any good examples you care to put forward?