The colder it's kept, the longer the shelf life, theoretically.

Are you talking about powders or liquids?

Liquids will benefit greatly from being kept cold. Powders it won't make much of a difference. Liquids in a fridge will be roughly 20C below room temperature and should theoretically last 2^2= 4 times as long as their listed shelf life, if they have one. And this is probably a gross underestimate of it, since they live longer than shelf life to begin with.

Vacuum sealed powders will probably last forever.