Breath is the power source for the voice. Not having enough breath or not having control of breath for singing or speaking can cause all kinds of vocal problems, including:
For breathing problems it's best to get to the cause(s) to find the breathing technique(s) that cure your issues. If you have organic lung damage, allergies or other medical condition, by all means see a doctor. But check this list out and you may be surprised at how much better your breath can get, pretty much immediately:
Is it too curved, collapsing your ribcage? Sit or stand taller which should straighten the curve out... but don't stiffen, stay flexible in your spine.
Have they become 'rib anchors'? Try using your hands to communicate... they will help keep your ribcage open, which is the prime fix for breath issues.
Is it balanced over your tailbone? Try moving it back until it is balanced over tailbone or heel instead of the balls of your feet.
Are they locked? Unlock them so you can have use of your legs for power.
Is it tight? Let go there... the belly should be able to naturally move open and then tighten low is such a way the the bottom of the ribcage stays wide.
Everything that goes into energy will affect your breathing (sleep, nutrition, physical exersize, etc.)
Especially when it comes to balancing breath support and breath control, vocal training can really improve your breathing for speaking and singing. Hit me up for a lesson in office, by phone or Skype, or buy my Power, Path and Performance vocal training course and conquer your breath problems once and for all.