April 29 (Reuters) - Everest Group posted a surge in first-quarter profit on Monday as the insurer benefited from stronger underwriting and better returns on its investments.

Supported by employer-guaranteed policies mandated by the government, insurance has lived up to its status as a "recession-proof" industry by staying resilient despite economic downturns.

The company said its gross written premium increased 17.9%, to $4.41 billion in the quarter.

It posted a combined ratio of 88.8%, compared with 91.2% a year earlier. A ratio below 100% means the insurer earned more in premiums than it paid out in claims.

Insurers also use their cash to shore up their portfolios, mainly by buying safe-haven assets such as U.S. Treasuries and other high-grade corporate bonds. Multiple rate hikes by the Federal Reserve in the past year have helped insurers earn higher interest from such investments.

Everest's net investment income improved to $457 million, compared with $260 million a year earlier, driven by a larger asset base and strong core fixed income returns.

Gross written premiums in its reinsurance segment grew 20.4% on a constant dollar basis.

Operating income was $709 million, or $16.32 per share, for the three months ended March 31, compared with $443 million, or $11.31 per share, a year ago. (Reporting by Sri Hari N S in Bengaluru; Editing by Pooja Desai)