We consider the cosmological effects of sterile neutrinos with the masses of 150 - 450 MeV .
The decay of sterile neutrinos changes the thermal history of the Universe and affects the energy density of radiation at the recombination and the big bang nucleosynthesis ( BBN ) results .
We derive severe constraints on the parameters of sterile neutrinos from the primordial abundances of helium-4 and deuterium .
We also find that in a particular model the constraints can be considerably relaxed by assuming a large lepton asymmetry in the active neutrinos .
In this case , the consistent parameters result in N _ { \mathrm { eff } } \simeq 3.2 - 3.4 and can alleviate the Hubble tension .