No O3 did not cause increase in damage markers. They are saying that in a couple of the O3 people they found an increase in a couple of the markers associated with decline, but there was no decline in function.
Memory function gets worse over time. The “markers” increase over time too. If the O3 helped, they do not know why. Correlation is not causation, but if you have no idea of the cause, correlation is all there is to look at.
Yes, I understand the correlation/causation difference. I just found it odd that they stated it only for the Omega-3 group. If it was natural progression and coincidence, then one would expect it to be uniform across all groups - the baseline as it were. So one can assume neither causation nor correlation without further study.