How do you accommodate a person who is fervently pessimistic when you are an eternal optimist?

A very close friend has had several disappointments in her life time that have led her to project a very negative and pessimistic attitude. She is rather unpleasant to be around as even the simplest of topics (say weather); turns into a diatribe on global warming or pollution. Every topic, no matter how serious or mundane, leads to a deeply negative and warning filled lecture.

Several other friends and even her own family members have commented to her about her prevalent negativity, and her response is usually very defensive and flippant. It seems not that her bar is set too high, but instead it’s just been removed. She is convinced she will always be let down. This approach is affecting her health and her life in general. She is frequently ill as she won’t take any meds to alleviate symptoms, so a simple cold will lead to bronchitis or a sinus infection. You see “medications never work for her like they’re supposed to, they usually have the exact opposite affect”.

Her sister recently suggested that perhaps she might be suffering from depression. The conflict that ensued was very hurtful to both of them. This is a life-long family friend, but honestly, I can barely stand to be around her anymore. I am most always optimistic although I am also a realist. I understand her psychological reasoning, but the constant negativity is draining. I’m at my wits end.