Health systems around the world must fundamentally restructure or collapse under the “tidal wave” of demand from people living with multiple serious health conditions, experts have warned.

In the NHS alone as many as 20 million people are living with two or more conditions and ineffective treatment is leading to escalating costs and early deaths.

The first report produced on the global burden of multimorbidity (multiple diseases) says it is an “enormous threat” affecting a quarter of the adult population and a billion people worldwide.

High income countries like the UK are seeing an “almost exponential increase” in health care costs where multimorbidity has risen, the report notes.

“We are facing a tidal wave of patients living with multiple long-term health conditions, and our report demonstrates how little we know about how to manage this,” said Professor Stephen MacMahon, chair of the Academy of Medical Science’s multimorbidity working group.

Rates of multimorbidity in the UK have rocketed in the past decade. One study included in the report shows that between 2002 and 2013 number of people over 50 with two or more diseases rose by half – from 31.7 per cent to 43.1 per cent.

Rises in obesity and cancers from preventable lifestyle factors are a major driver, as is the increase in life expectancy around the world.

But this is not the full picture as multimorbidity is increasingly common in younger people and developing nations, where survival improvements from diseases such as HIV may result in more respiratory diseases.

Caring holistically for these complex patients, instead of treating each part of their condition separately, relies on a move away from the ultra-specialised medical model and a change in how we structure drug trials.

But the ACM’s report, released today, says there is a lack of information on the causes and extent of multimorbidity, and the best ways to address it.

“I estimate tens of millions of Britons suffer from multimorbidity, and globally the number could be a billion,” Professor MacMahon added.

“While we know multimorbidity is increasing, we don’t know how quickly or which groups are experiencing the biggest increases. This report should be the tipping point of recognising that multimorbidity is an enormous threat to global health.”

In some cases having one condition, such as heart disease, logically increases your risk of others, like circulatory diseases which can lead to a stroke.

In other cases the clustering of multiple conditions is less immediately obvious: people with type 2 diabetes are also more at risk of respiratory diseases like COPD, for example.

The report says there are particularly complex relationships between mental health and physical diseases, and most profoundly in the growing population of people with dementia.

But the NHS reliance on 10-minute GP appointments, at which most patients are managed, means patient care is only focused on the most pressing problem, the authors warn.

Medical specialisation has also meant patients see multiple single-disease specialists but receive worse care for each one of them, and this means their health and quality of life suffers.

“It can be a full time job, being a patient,” said Dr Lynne Corner, director of engagement at the Newcastle University Institute for Ageing and Faculty of Medical Sciences.

“It’s not unusual for someone to have five different appointments in five days with five different teams in five different clinics.”

In parts of the UK, such as the Clinics for Research and Service in Themed Assessments in Newcastle, patients can visit multiple specialists in one trip, and Dr Corner added it was important this was rolled out more widely.

Professor Melanie Davies, a member of the working group and a professor of diabetes medicine at Leicester University, said the growth in people under 40 coming to her with Type 2 diabetes was a “real concern”.

While adolescent Type 2 was almost unheard of 20 years ago there are now more than 500 children with the condition in the UK, she added.

As these patients are on lifelong medication, more trials are needed to look at medications which work across several conditions.

“As smarter medicines come along we are looking for them to have other benefits beyond a single disease,” Professor Davies told The Independent.

“They are developing diabetes drugs which are associated with weight loss, a much lower risk of hypoglycaemia (low blood sugar), and that lower blood pressure as well – and we’re looking at their impact on cardiovascular disease.”

Management is particularly hard where a patient has a condition like dementia, which can be made worse by medications for other diseases and makes keeping on top of complex care regimes much harder.

Dr Alison Evans, Alzheimer’s Research UK’s head of policy and impact, said the report was a good foundation, but more work was needed in this growing group.

“Many of the health conditions that accompany dementia, like diabetes, urinary infections and depression, go untreated costing the UK £995m a year, according to a recent study,” she added.