  Mesonic and nucleon fluctuation effects are investigated in medium. We couple
the nucleon field to the $2+1$ flavor meson model and investigate the finite
temperature and density behavior of the system, in particular, the axial
anomaly function. Somewhat contrary to earlier expectations we find that it
tends to strengthen at finite density. At lower temperatures nucleon density
fluctuations can cause a relative difference in the $U_A(1)$ axial anomaly of
about $20\%$. This has important consequences on the mesonic spectra,
especially on the $\eta-\eta'$ system, as we observe no drop in the $\eta'$
mass as a function of the baryochemical potential, irrespective of the
temperature. Based on the details of chiral symmetry restoration, it is argued
that there has to be a competition between underlying QCD effects of the
anomaly and fluctuations of the low energy hadronic degrees of freedom, and the
fate of the $U_A(1)$ coefficient should be decided by taking into account both
effects simultaneously.
