In the local universe, galaxy properties are highly correlated with the environment. For example, the biggest overdensities known to as galaxy clusters host significantly older, more massive and spheroidal shaped galaxies compared to the field. In order to understand how these massive structures formed from the primordial density fluctuations of the dark matter distribution, we need to study their progenitors in the distant universe. These candidate (proto)clusters are usually identified as overdense regions of galaxies in multi-wavelength surveys. However, at higher redshifts it becomes increasingly difficult to find them because of their more loosely distributed members and the large spectroscopic redshift incompleteness. In this seminar, I will present an analysis of the dense structures identified in the CDFS and UDS fields in the redshift range between 2 and 4, when we expect to have the earliest fingerprint of the environment on galaxy evolution. These two fields, already well studied in the literature, take the advantage of the VANDELS survey, which has recently observed and characterized spectroscopically more than 1 thousand galaxies at this cosmic epoch, hence improving the accuracy of the galaxy density maps and of the identified overdensity structures. Thanks to the available VIMOS spectra and complementary MOSFIRE data, I will present the stellar and gas-phase mass-metallicity relations in overdense regions and in the field, and compare the observational findings to the predictions of semi-analytic models and hydrodynamical simulations. These results set the ground for more systematic investigations of overdensities at z > 2 that will be performed in wider fields with forthcoming facilities in the next decade.