Historically low real interest rates

Negative real bond yield effectively mean than, by investing in an US Treasury, bond investors are currently losing money at constant purchasing power. The current US real interest rates are the lowest in 40 years. Real interest rates have been more negative only for 10 months in the last 70 years, namely 1974, 1975 and 1980. To us, this looks unsustainable and a good moment to own some gold or gold miners in our portfolios.