People with learning disabilities are dying on average 16 years earlier than they should, because the NHS does not properly investigate and treat their physical complaints, an inquiry has found.

A confidential inquiry into deaths in the south-west, carried out by Bristol University academics and funded by the Department of Health, has revealed stark inequalities and recommends the creation of a review body to investigate and monitor learning disability deaths across the UK.

The charity Mencap estimates from the review findings that more than 1,200 children and adults die every year because they are not getting proper NHS care. More than a third (37%) are not getting the healthcare they should.

"A scandal of avoidable deaths on the scale of Mid Staffs takes place every year for people with a learning disability in the NHS. These deaths, caused by poor care and delays in diagnosis and treatment, highlight the scale of discrimination faced by disabled patients in the NHS," said Jan Tregelles, the acting chief executive of Mencap.

The confidential inquiry into the premature deaths of people with learning disabilities (CIPOLD) examined the sequence of events leading up to death of all known adults and children with learning disabilities in five primary care trusts of the south-west over a two-year period – 233 adults and 14 children.

They also examined the illnesses and deaths of 58 other adults without learning disabilities but of similar background and state of health for comparison. They found that 22% of people with learning disabilities die before the age of 50, compared with just 9% of the rest of the population.

Other adults were more likely to die prematurely because of smoking, alcohol and a poor diet – all factors connected with lifestyle.

People with learning disabilities, however, were more likely to die early because there were delays or problems with investigating, diagnosing and treating their illnesses. They were also more likely to have problems in having their needs identified and getting the appropriate care. Their families or carers had more problems in getting their views heard and listened to. The review team says premature deaths could be avoided by better health and social care.

Dr Pauline Heslop, the study's lead author at the University of Bristol Norah Fry Research Centre, said: "This report highlights the unacceptable situation in which people with learning disabilities are dying, on average, more than 16 years sooner than anyone else. The cause of their premature death is not, like many in the general population, due to lifestyle-related illnesses.

"The cause of their premature deaths appears to be because the NHS is not being provided equitably to everyone based on need. People with learning disabilities are struggling to have their illnesses investigated, diagnosed and treated to the same extent as other people. These are shocking findings and must serve as a wakeup call to all of us that action is urgently required.