Surely as a Voiceover Artist, all you have to do is stand there (or sit) and read out loud. Why do you need to take care of your health when the job is so easy?
If you are ill or not well or not on top form you will sound like it. Legendary DJ Tony Blackburn was much criticised during the height of his fame for his cheesy happy sound. He sounded happy because he was actually smiling!
Practise, Practise, Practise
If you have a cough or a cold you sound different- your nose is blocked and you find it hard to breathe and may wheeze too. So therefore you cannot work.
Once very highly respected Voiceover Artist who we met at Vox 2015 says he doesn't drink alcohol. At all. Because it affects how he sounds when voicing at 6am. Other voice talent won't voice before 10am as they don't sound awake enough.
Getting regular exercise is also a good idea - if you are unfit your breaths will be much heavier. So, get fit and learn how to breathe from your abdomen.
Make sure you can hear properly - and can tell when a take is bad and why.
Before glasses were needed
Make sure your eyes are good - and get them checked regularly. When I was reading the news on BBC Radio 2 I slowly found it increasingly hard to focus on the scripts - which initially I put down to tiredness due endlessly-changing shifts. But no, I was just the wrong side of 40.
I now wear glasses to read all my voiceover scripts. And I insist on 14 point font for the scripts.