Courtiers insisted that the Queen's diary was as busy as ever and played down any suggestion that her health had played a part in the decision.
Despite her hospital stay earlier this year, when she was treated for gastroenteritis, she remains in good health and went riding at Windsor on Friday.
Buckingham Palace dismissed any suggestion that the Queen's absence had anything to do with controversy over the summit because of human rights abuses in Sri Lanka.
Stephen Harper, the Canadian Prime Minister, has said he will boycott the meeting and has demanded an inquiry into claims that 40,000 people were killed by Sri Lankan troops in 2009.
A spokesman said the decision not to attend was part of a review of the amount of long-haul travel undertaken by the monarch and the Duke of Edinburgh, who will be 92 next month.
Apart from highlighting the Queen's age, the decision has also been seen as a symbolic moment in Prince Charles' preparation for kingship.
- staff reporter, agencies