The research, from Barnett Waddingham, showed that more than 220 companies in the index sponsor a defined benefit scheme.
The sharp rise in the deficit at the end of May, just 12 months after it hit £40bn, comes after a period of immense volatility in global markets driven by the European sovereign debt crisis.
Some groups in the FTSE 350, particularly the industrial sector, have been more exposed to falls in the levels of pension scheme funding over the last year, said actuary Barnett Waddingham.
At the same time pension funds have been hit by the Bank of England’s £325bn programme of quantitative easing (QE).
“Government gilt yields have fallen in large part because of quantitative easing. Companies are having to reassess the amount that is being paid in,” said Nick Griggs, head of corporate consulting at Barnett Waddingham.
“You have to take a view whether a fall in bond yields is a temporary issue or whether it is permanent.”