  We show that a mass-varying neutrino model driven by scalar field dark energy
relaxes the existing upper bound on the current neutrino mass to ${\sum m_\nu <
0.72}$ eV. We extend the standard $\Lambda$ cold dark matter model by
introducing two parameters: the rate of change of the scalar field with the
number of $e$-folds and the coupling between neutrinos and the field. We
investigate how they affect the matter power spectrum, the cosmic microwave
background anisotropies and its lensing potential. The model is tested against
Planck observations of temperature, polarization, and lensing, combined with
baryon acoustic oscillation measurements that constrain the background
evolution. The results indicate that small couplings favor a cosmological
constant, while larger couplings favor a dynamical dark energy, weakening the
upper bound on current neutrino masses.
