Five years is actually not a long time for science to understand a process as complex as the pathways of the oil after a large spill. Some of the impacts of the Deepwater Horizon spill on the marine life and ecosystems of the Gulf of Mexico will only become visible in future years. We use oil products daily.
First the researchers examined the effects of lowering cortisol to below a normal (or baseline) level. Then they compared the effects of low, medium, high, and very high cortisol levels in patients undergoing cardiac surgery, a procedure that causes a lot of inflammation.
Cortisol is a powerful anti-inflammatory hormone, so you might think that high levels of it would protect us from inflammatory diseases like arthritis and heart disease. Unfortunately, it doesn't. Cortisol and cortisol-like medicines suppress inflammation by suppressing parts of the immune system. That makes us more susceptible to new infections, and sooner or later we will get them. The new infections will raise our inflammation and cortisol levels, making us susceptible to still more infections. And so on.