Columbus-based insurer Aflac said Tuesday its third quarter profit rose 38 percent to $1.02 billion, boosted by investment gains and a lower tax rate.

Aflac said total revenue in Japan, its largest market, increased 8.9 percent, while U.S. division revenue rose 5.2 percent, compared to the third quarter of 2011.

Aflac’s per share earnings were $2.16 compared to $1.57 in third quarter last year, buoyed by net after-tax investment gains of $186 million. On an operating basis, not including investment income, Aflac earned $832 million or $1.77 per share, vs. $770 million or $1.65 per share a year ago.