Its unlikely that such accounts can be used as collateral unless the investments are liquidated and the cash there is used. If its an retirement account (401k, ira), anything pulled or taken from such accounts would be taxable to them unless its a roth ira then any contributions wouldnt be taxable. If they have an non-retirement investment account with a brokerage and have stocks and whatnot, they could just borrow against margin. If its all just plain cash in the accounts, they could just use it instead of asking for a loan.