Deficits of schemes monitored by the Pension Protection Fund (PPF) worsened last month, increasing from £8.3bn in June to £67.3bn at the end of July.
The funding ratio for the 6,533 schemes in the PPF 7800 Index fell from 99.2% to 93.7%, with total assets at £1001.4bn and liabilities at £1068.7bn.
Out of these, 4,684 schemes were in deficit and 1,849 schemes in surplus.
The lifeboat fund said equities were the biggest drivers behind the changes in scheme assets but falling gilt yields also hit performance.
The PPF said: "The FTSE All-Share Index fell by 2.3% over July and 15-year gilt yields were down 42 basis points.
"During the month of July there was a 0.26% decrease in assets mainly due to declining UK and global equities, with some offset from higher bond prices.
"Liabilities also rose, by 5.6%, due primarily to the significant fall in gilt yields."
The 7800 Index also showed the aggregate deficit of all schemes in deficit at the end of July increased to £116.7bn from £77.6bn a year earlier.
The total surpluses of schemes in surplus decreased to £49.4bn from £69.3bn at the end of June.
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