  The discrepancies in different measurements of the lifetime of isolated
neutrons could be resolved by considering an extra neutron decay channel into
dark matter, with a branching ratio of the order of $O(1$\%). Although the
decay channel into a dark fermion $\chi$ plus visible matter has been already
experimentally excluded, a dark decay with either a scalar or dark photon
remains still a possibility. In particular, a model with a fermion mass
$m_\chi\approx 1$ GeV and a scalar $m_\phi \approx O(\rm{MeV})$ could provide
not only the required branching ratio to explain the anomaly but also a good
dark matter (DM) candidate with the right thermal abundance today. Although the
interaction DM-neutron will affect the formation of neutron stars, the combined
effect of the dark matter self-interactions mediated by the light scalar and an
effective repulsive interaction with the neutrons induced by the scalar-Higgs
coupling would allow heavy enough neutron stars. The combined constraints from
neutron lifetime, dark matter abundance, neutron star and Higgs physics, and
Big Bang Nucleosynthesis, restrict the light scalar mass to the range $2 m_e <
m_\phi < 2 m_e + 0.0375$ MeV.
