The survey was commissioned to support the launch of lifestyle advice website NHS MidLifeCheck. It showed almost half of those aged 45-67 years believe they should think more about a healthy lifestyle.
But 47% of those questioned say they are ‘all talk and no action', according to the survey.
Over 50,000 people have visited the site since its launch on 8 February - three times the predicted number, the DoH said.
The website has been launched to inspire healthier lifestyles among middle aged people, as well as to reduce health inequalities, outlined recently in the Marmot Review.
The survey showed a ‘stark contrast' between how affluent and disadvantaged groups view their own wellbeing.
People with low incomes were more than twice as likely to say they had poor health. They were also almost twice as likely to feel they are unfit and twice as likely to say they know little about their own health and fitness.
Low income groups were also more likely to be unhappy, the DoH research said.
CMO Sir Liam Donaldson said: 'Most people in their 40s generally enjoy good health, however for some people certain chronic health issues can start at this age - with cancer, heart disease and diabetes being some of the biggest causes of death.
‘We all need to be aware of how to help prevent potential health problems,' he added.
Website users answer a questionnaire that returns personalised results and advice to improve lifestyle choices, including topics such as smoking, diet and exercise, and emotional wellbeing.