Britons will live longer but will be afflicted by more illnesses within the next two decades, a new study warned.
The number of older people diagnosed with four or more diseases will double between 2015 and 2035.
And a third of these will be diagnosed with dementia, depression or a cognitive impairment, it has emerged.
Within the next 20 years, British men and women over 65 are expected to live 3.6 years and 2.9 years longer than older Britons now.
However, there will also be a massive expansion in the number of people suffering from multiple diseases, known as multi-morbidity.
Men will live on average of 18.6 years and women 21.2 years past their 65th birthday.
But five-and-a-half years of the extra years in men and five years in women will be spent with multi-morbidity and two-thirds or more of the gain in life expectancy will be spent with four or more diseases.
And Britons under 65 who are overweight or obese and do little exercise are a ticking time bomb, with the increased illnesses posing a challenge to the NHS and social care, Newcastle University’s Institute for Ageing warned.
Carol Jagger, Professor of Epidemiology of Ageing, said: “Healthcare delivery was built...on the treatment of single diseases. Over the last decade, the growing number of older people aged 65 years and over has become a considerable challenge to health and social care service provision and funding, as over 50 per cent have at least two chronic conditions – multi-morbidity.
“Moreover, numbers of the very old, aged 85 years and over, are set to double over the next 20 years, with multi-morbidity the norm in this age group.
“Multi-morbidity increases the likelihood of hospital admission, length of stay and readmission, raises healthcare costs, reduces quality of life, and increases dependency, polypharmacy and mortality.
“In addition to multi-morbidity, many of the very old have sensory impairment and incontinence, making a single disease-focused model of healthcare unsuitable.
“Poor health behaviours such as obesity and physical inactivity are risk factors common to a number of diseases, but have received little attention as risk factors for multi-morbidity. Younger cohorts have a higher prevalence of obesity, which may contribute to the increased prevalence of multi-morbidity in those under 65 years of age.”
Prof Jagger added: “Much of the increase in four or more diseases – complex multi-morbidity – is a result of the growth in the population aged 85 years and over.”