Hi, I have bad acid reflux and have had it for years. I recently tried apple cider vinegar diluted in water for health purposes. Well, I don't know if it helped my immune system, but one thing is for sure, it made my acid reflux and heartburn flare up WORSE THAN EVER right after drinking it, and the pain lasted for an hour. This was on multiple occasions. I think there are different kinds of gastritis, not all acid reflux disease has the same root cause.