She told delegates their jobs were being made 'all the harder when the reality that you are creating is so different from the myths we keep hearing'.
Ms Hewitt began by thanking delegates. She said: 'Thank you to each and every one of you for what you have done in the last 12 months, a very difficult and often bruising 12 months and you have restored the NHS to financial health and done that alongside so much else.'
She added: 'The reality is that you and your colleagues over the last 12 months have cared for more patients, you have brought the waiting lists down, patient satisfaction has gone up, the clinical outcomes are better and, of course, you have done that all at the same time as restoring financial control.'
Ms Hewitt said it was a 'myth' that the public had lost so much confidence in NHS services that they were resorting to private treatment.
'The reality is that except for cosmetic surgery, the amount people spend on private healthcare and private health insurance has been going down, not up,' she said.
She went on: 'That's the reality. Of course, you don't read about it in the press, but we are not going to make policy on the basis of the headlines. So I thank you for persisting with very difficult changes in very difficult times.'
Ms Hewitt urged managers to 'take control of [your] own destiny, not looking upward to the Department of Health for instructions or permission but looking outwards'.
Reforms such as practice-based commissioning gave managers more scope to improve service locally, she said.
Managers should 'seize and use these freedoms that increasingly you have got'.
Ms Hewitt added that the government was transforming the NHS 'from a top-down centralised command and control organisation' into a 'truly patient-led public service'.
Asked in the question and answer.session after her speech.about the Conservative Party's white paper policy document on the NHS, Ms Hewitt said she agreed with elements such as more choice and foundation trusts, areas she said the government is already pursuing.
But she added: 'There are other things I strongly disagree with, particularly the idea of hospitals going back to competing on price rather than quality and GP practices negotiating a price with all the hospitals that patients might go to.'
Responding to concerns about further reorganisations of trusts, she said: 'We do have the right structures and we should leave them there.'
On the party's calls for NHS independence, she said: 'Handing [the NHS] over to one independent board is frankly a distraction from the real business of making sure you on the front line in your different organisations have the freedom, have the autonomy and independence within a proper framework of accountability and more choice and control for patients to get on with delivering the best possible care.'