TOM MURPHYUnitedHealth Group's third-quarter net income jumped 23 percent, and the nation's largest health insurer raised its 2012 earnings forecast for the third time this year. But company leaders also cautioned against thinking too positively about 2013. They said Tuesday that a stubbornly slow economy and the health care overhaul will combine to pressure the insurer's business again in the new year. The Minnetonka, Minn., company now expects 2012 earnings of $5.20 to $5.25 per share, up from its previous forecast for $4.90 to $5 per share. Analysts expected $5.13 per share. CEO Stephen J. Hemsley told analyst during a Tuesday conference call, the insurer expects growth in 2013 as well. But he said UnitedHealth must deal with tight government budgets that will squeeze its Medicare and Medicaid businesses and high unemployment rates that could hamper its private insurance enrollment. The massive health care overhaul, which aims to cover millions of uninsured people, also will affect results next year. The law calls for a tax on premiums to start in 2014, but Hemsley said that will start to affect UnitedHealth's performance next year because the insurer will have to account for it in the rates it charges. Insurers set their prices based on the claims or expenses they expect to have in future. "We expect to grow revenues and earnings per share in 2013, but we view the current consensus level as a considerable challenge from this distance given these market conditions," he said. Analysts expect, on average, earnings of $5.63 per share next year. Hemsley also outlined concerns about the economy and employment levels last fall, as the insurer headed into 2012. UnitedHealth then went on to beat analyst expectations in every quarter so far this year. The CEO said Tuesday his company has successfully handled the broader market challenges it faces, but those obstacles still remain.