1. Modal verb for possibility: "can have a really negative impact" uses 'can' to talk about possible effects, which is a common and natural way to discuss consequences.
2. Present simple tense: The answer uses present simple tense throughout ("leads to", "weakens", "catch"), which is appropriate for talking about general truths and facts.
3. Conditional clause: "If someone is under stress for a long period, it can even increase the risk..." uses a first conditional structure to talk about possible future outcomes, showing good control of complex sentences.
4. Passive voice: "when they're stressed out" uses the passive form to describe a state, which adds variety to sentence structure.