Japan's monetary base grew 3.9 percent in January from a year earlier for the 48th consecutive monthly increase, the Bank of Japan said Wednesday.

The average daily balance of the monetary base -- cash in circulation plus current-account deposits held at the central bank by financial institutions and Japan Post -- totaled 112.513 trillion yen in the reporting month, the BOJ said.

The long-running expansion in the monetary base reflects the BOJ's quantitative monetary easing policy adopted in March 2001 to fight deflation.