Miyako Suda, who opposed the Bank of Japan's ultraloose monetary policy as a member of its Policy Board, has a warning for the nation's life insurers as bond yields sink ever lower.

This prolonged period of ultralow rates will pressure profits as sovereign debt matures and has to be replaced with lower-yielding bonds, said Suda, who is now an external board member at Meiji Yasuda Life Insurance Co.

"As the duration of their JGB holdings shortens, insurers' profitability will worsen if yields stay below zero," the 71-year-old said in an interview in Tokyo. "If they don't change direction now, they will become poorer and poorer. The negative impact will become evident."