The chief investment officer of Calpers, the largest U.S. public pension fund, recently said shifting assets out of U.S. stocks into international investments could boost returns from its $250 billion portfolio.

One scenario under consideration calls for the California Public Employees' Retirement System to reduce its U.S. stock position to 24 percent of total assets from 40 percent, the fund's CIO Russell Read said at a public board meeting Nov 19.

Such a move would represent the lowest level of U.S. stock holdings in more than two decades.