Shares of supplemental insurer Aflac (NYSE:AFL) just hit their highs for the year after the company released first-quarter earnings. Aflac is still struggling in its core Japanese market, but trends could be turning, and business here at home has a lot of potential.              

Our recent Fool by Numbers will waddle you through the first-quarter details, but here's a brief rundown. Total revenue grew 5%, made up of growth in the following key insurance metrics: premiums earned (up 5%) and net investment income (up 8%). Earnings posted a double-digit advance, continuing an enviable track record of operating income growth as defined by the company.

Aflac Japan accounted for close to 75% of operating earnings for the quarter and has been seeing double-digit decreases in new sales. Total profitability has held up, though, and although management expects another sales decrease for the coming quarter, it sees an increase during the second half of the year as comps become easier and a new sales director begins to put his stamp on the region.

United States trends continued to be positive on most levels, including double-digit improvements in new sales and premium income. A number of analysts believe Aflac will again grow in Japan, but the most potential exists here at home, and the company's wacky duck mascot has done wonders in building brand awareness.

No matter which market the company expands into going forward, its business has appeal and is somewhat unique. To enhance traditional insurance, Aflac offers individuals additional coverage against the threat of illness and injury. This could become increasingly important as baby boomers reach their golden years. Peers such as Conseco (NYSE:CNO), AIG (NYSE:AIG), UnumProvident (NYSE:UNM), and Assurant (NYSE:AIZ) offer similar products, but Aflac is the best pure play on supplemental insurance.

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Fool contributor Ryan Fuhrmann is long shares of Aflac but has no financial interest in any other company mentioned. Feel free to email him with feedback or to discuss any companies mentioned further. The Fool has an ironclad disclosure policy.