726.1 When is a disability insurance benefit reduced for age payable?
A disability insurance benefit reduced for age may be payable if you are already entitled to either retirement insurance benefits or reduced widow(er)'s insurance benefits. This is true whether or not your benefit is based on disability.
726.2 What if a disability insurance benefit becomes payable to a beneficiary entitled to a reduced retirement insurance benefit?
If a disability insurance benefit becomes payable to you after becoming entitled to retirement insurance benefit, your disability benefit is reduced by the amount your retirement benefit is reduced for the months prior to the month of entitlement to the disability benefit in which you received retirement benefits.