  We propose a correction to the coefficient of nuclear-spin diffusion by a
factor $1/\sqrt{1-\overline{p}^{2}}$, where $\overline{p}$ is the average
nuclear-spin polarization. The correction, derived by extending the Lowe-Gade
theory to low-temperature cases, implies that transportation of nuclear
magnetization through nuclear-spin diffusion accelerates when the system is
hyperpolarized, whereas for low-polarization the correction factor approaches
unity and the diffusion coefficient coincides with the conventional diffusion
coefficient valid in the high-temperature limit. The proposed scaling of the
nuclear-spin diffusion coefficient can lead to observable effects in the
buildup of nuclear polarization by dynamic nuclear polarization.
