The end of the electron energy distribution dN \over dE in \beta decays of nuclei depends on neutrino masses and mixing angles. Various approximate parametrization of the dN \over dE, proposed in literature, and the definition of effective neutrino masses m_\beta are investigated. Bounds or future measured values of m_\beta together with the oscillation parameters are a source of information about the mass of the lightest neutrino.

PACS numbers: 14.60.Pq, 26.65.+t, 95.85.Ry