  We calculate the isoscalar axial-vector coupling constants of the Lambda
hyperon using the method of QCD sum rules. A determination of these coupling
constants reveals the individual contributions of the u, d and the s quarks to
the spin content of Lambda. Our results for the light-quark contributions are
in agreement with those from experiment assuming flavor SU(3). We also find
that the flavor-SU(3)-breaking effects are small and the contributions from the
u and the d quarks to the Lambda polarization are negatively polarized as in
the flavor-SU(3) limit.
