[GNC] How to account for insurance policy profit participation?

[rsbrux]

We have an insurance policy with a guaranteed return at maturity as well 
as profit participation (Überschussbeteiligung) which is calculated 
annually.  Presumably both are some kind of investment income, but it is 
unclear to me how to account for them.  I suspect that the guaranteed 
return should be classified as interest, but should I record it in 
GnuCash annually or only at maturity?

The profit participation is a complete mystery to me.  This is a share 
of the insurer's profits which accrues to the policies in years when the 
insurer achieves haigher returns on its (capital) investments than a 
predetermined threshold.  Is this a capital gain?  How should I record it?