I have been advised to have a brake line flush the next time I have my oil changed. Is this necessary?
brake fluid gets old, just like any other fluid in a car or truck. In addition, there is some break down due to heat in cylinders on overused brakes. Check your owners manual to see how often the mfg. recommends the brake fluid change, and follow the service instructions. Do not mix different brake fluids. Be sure to have this done by a professional who knows what he or she is doing, unless you can do it yourself, which your question suggests you cannot.
Another thing that brake fluid does is attract moisture (it is hydrophylic). Water in brake fluid is bad. So yes - brake fluid changes are recommended, though as ignoramus said your service schedule should include info about intervals.
Good responses. Yup, it may be time.
I just had mine done a few weeks ago along with my brakes. Ummmm…I should in full disclosure point out that the labor and bays are free to me and the materials are 20% off…and I’m disabled. As cigroller sugested, you should probably have yours done. Brakes are so critical that it’s better to have someone knowledgable do them.
Don’t you mean brake fluid is hygroscopic?
Tester
I think that brakes could be considered hydrophobic (fear of water).
Shop around for brake flushing service. Prices can vary.
Vehicles with ABS system can bring added complications. The repair facility had best know if there are any, in any particular vehicle.
I advise getting brake fluid changed every 3 years.
Well, I suppose if you want to be literal about it then yes. Hydrophylia would be the “love” of water or having an “affinity” for water. So, given that brake fluid is incapable of such emotional things - then yes, hygroscopic - or readily absorbing moisture - would maybe be more appropriate since it doesn’t imply thought or emotion on the part of the brake fluid 
Hey OP - your brake fluid will absorb moisture, though I don’t know if you want to think that it “loves” it.