Investors are gobbling up residential real estate with cash, pushing national home prices lower, according to the latest Campbell/Inside Mortgage Finance HousingPulse Tracking Survey.

The overall proportion of cash buyers in the housing market soared to a record 33.2%, compared to 29.6% a year earlier.

Meanwhile, the investor class relied heavily on cash to buy homes, with 74% of investors using cash to buy homes in December.

Investors represented 22.8% of home purchases in December alone, up slightly from 22.2% a month earlier.

The study says investor bids are bringing prices lower by waiting for other buyers to lose bids through the extensive mortgage approval process. The study says investors are nabbing properties at lower prices when other buyers lose bids during the extensive mortgage approval process or appraisals.

Real estate agents that responded to the survey said investors usually offer 10% to 20% below the listing price up to a price of $250,000.

Write to Kerri Panchuk.