  We present the results of a joint investigation aimed at constraining the
primordial He content ($Y_P$) on the basis of both the Cosmic Microwave
Background (CMB) anisotropy and two stellar observables, namely the tip of the
Red Giant Branch (TRGB) and the luminosity of the Zero Age Horizontal Branch
(ZAHB). Current baryon density estimates based on CMB measurements cover a wide
range values $0.009\la \Omega_bh^2 \la 0.045$, that according to Big Bang
Nucleosynthesis (BBN) models would imply $0.24\la Y_P \la 0.26$. We constructed
several sets of evolutionary tracks and HB models by adopting $Y_P=0.26$ and
several metal contents. The comparison between theory and observations suggests
that ZAHB magnitudes based on He-enhanced models are 1.5$\sigma$ brighter than
the empirical ones. The same outcome applies for the TRGB bolometric
magnitudes. This finding somewhat supports a $Y_P$ abundance close to the
canonical 0.23-0.24 value. More quantitative constraints on this parameter are
hampered by the fact that the CMB pattern shows a sizable dependence on both
$Y_P$ and the baryon density only at small angular scales, i.e. at high l in
the power spectrum ($l\ga 100$). However, this region of the power spectrum
could be still affected by deceptive systematic uncertainties. Finally, we
suggest to use the {\em UV-upturn} to estimate the He content on Gpc scales. In
fact, we find that a strong increase in $Y_P$ causes in metal-poor, hot HB
structures a decrease in the UV emission.
