  We re-evaluate the zero point Casimir energy for the case of a massive scalar
field in $\mathbf{R}^{1}\times\mathbf{S}^{3}$ space, allowing also for
deviations from the standard conformal value $\xi =1/6$, by means of zero
temperature zeta function techniques. We show that for the problem at hand this
approach is equivalent to the high temperature regularization of the vacuum
energy, as conjectured in a previous publication. Two different, albeit equally
valid, ways of doing the analytic continuation are described.
