No, if that were the case natural selection would not take place and Darwin would not be famous! In normal circumstances only the fittest survive and breed.
what he said....
Some people sadly have genetic "abnormalities" that means that they're predisposed to certain diseases.
An extreme example would be Huntington's (chorea) which is 100% genetic. Either you have a mutation on a gene on chromosome 4 or you don't : there's no environmental influence at all. If you have it you're guaranteed to show symptoms (and die). If you don't you're fine.