Mental ill-health is costing the UK more than £94bn every year, counting treatment, social support costs and the losses to the economy from people who cannot work, according to the OECD.

The Organisation for Economic Co-operation and Development’s report shows the whole of Europe is struggling with the burden of mental ill-health, which affects an estimated 84 million people – one in six. The cost to the UK economy is in line with the average for Europe at 4% of GDP. Nearly half the UK costs (£42bn) are indirect costs related to lower employment and productivity.

“It is a challenge in virtually all countries,” said Gaetan Lafortune, one of the report’s authors. “We are not signalling that any country would be the model to follow. The general message is the need for a greater priority on the promotion of mental health and improving services.”

The report looks at ways to help people of all ages with mental health problems. Schools “are an ideal setting for interventions”, says the report, citing a survey that showed 11% of children aged 11, 13 and 15 had been bullied at least once by some form of internet message or posting.

The mental health of unemployed and older people was also of great concern. The report highlighted efforts in England to combat loneliness with lunch clubs and befriending services.

Health at a Glance is a major annual review by the OECD of the extent of ill-health, prevention and care across the European Union. It shows a slowdown across Europe in rising life expectancy as the drop in cardiovascular deaths – including heart attacks and strokes – slows down, possibly linked to lifestyle issues including obesity and alcohol.

More than 1.2 million people die prematurely in Europe every year. Of those deaths 790,000 are linked to tobacco smoking, alcohol consumption, unhealthy diets and lack of physical activity.

This year the report says that improving people’s mental health should be a Europe-wide priority. In 2015, it says the deaths of 84,000 people were attributed to mental illness or suicide. Anxiety disorder affects 25 million, more than 5% of the population. Depressive disorders affect 21 million or 4.5%, while 11 million have alcohol and drug disorders and 5 million have severe illnesses such as bipolar disorders.

Finland, the Netherlands, France and Ireland have the highest rates of mental health disorders with more than 18% of people affected, while in the UK it is 17.7%. The rates may be higher in some countries partly because there is more willingness to seek medical help and less stigma.

The report looks at waste in health services, which are all struggling with costs. It estimates that up to one-fifth of health spending could be eliminated by measures including ending unnecessary investigations and using generic medicines. It cites the incentive payments to NHS hospitals to carry out procedures as day surgery rather than keeping people in overnight. The UK does less well in moving patients out of hospital to avoid “bed blocking”.

Staffing is an issue. Data collected by the OECD but not included in the report shows that the number of registered nurses working in the UK who trained in Europe dropped from 8,000 in 2016 to just 800 in 2017.

“This huge drop in the number of nurses coming to work in Britain from EU countries is extremely worrying, especially when the NHS has at least 42,000 vacant nursing posts,” said Donna Kinnair, the Royal College of Nursing acting chief executive and general secretary.

“The government left it far too late to send out the message that healthcare professionals working here are desperately needed, and that they will be given priority in the Brexit negotiations. It is therefore no surprise that large numbers of nursing staff from EU countries have been put off coming to work here.”

Jo Bibby, director of health at the Health Foundation, said the report highlighted the importance of good health to the UK’s prosperity.

“With life expectancy stalling and health inequalities widening, it is time that our nation’s health is treated as an asset to be maintained and improved over the lifetime,” she said.

“While older people are more likely to experience mental health problems, such problems are also a growing issue among younger people. It is important that strategies to improve health, including mental health, take a life course approach starting from the early years, the transition into adulthood and right through to older ages. There are also stark inequalities with the poorest fifth in the UK almost three times as likely to report a mental health problem as the richest fifth and the underlying causes of health including poverty must be addressed to tackle this.”

• In the UK, Samaritans can be contacted on 116 123 or email jo@samaritans.org. In the US, the National Suicide Prevention Lifeline is 1-800-273-8255. In Australia, the crisis support service Lifeline is 13 11 14. Other international suicide helplines can be found at www.befrienders.org.