A third of middle-aged adults in Britain have multiple chronic health issues, research suggests.
Scientists from University College London (UCL) analysed nearly 8,000 adults born in 1970, dubbed Generation X.
Among those aged 46 to 48, 33% had two or more health complaints – including recurrent back pain, high blood pressure, mental health disorders, diabetes and high-risk drinking.
Results, published in the journal BMC Public Health, further show those who were born into the most deprived families were more at risk of multiple health complaints in midlife.
Amid calls for policy changes to protect the most vulnerable, one expert has warned "the health of British adults in midlife is on the decline".
"This study provides concerning new evidence about the state of the nation's health in midlife," said lead author Dr Dawid Gondek.
"It shows a substantial proportion of the population are already suffering from multiple long-term physical and mental health problems in their late forties.
"Compared to previous generations, it appears the health of British adults in midlife is on the decline".
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The UCL scientists analysed more than 7,900 people who were born in the same week in 1970, who have taken part in the British Cohort Study ever since.
When they reached their mid-to-late forties, the participants' blood pressure and diabetes status were measured. Questionnaires also revealed whether they were enduring a range of chronic physical or mental health complaints.
The results reveal 33% of the participants had multiple chronic health issues.
High-risk drinking affected just over a quarter (26%) of the participants, while around one in five (21%) endured recurrent back issues or mental health problems (19%).
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Just under one in six (16%) had high blood pressure, while 12% reported either asthma or bronchitis. Arthritis and diabetes affected 8% and 5% of the participants, respectively.
The most common combinations were mental health issues with either high blood pressure, asthma or arthritis.
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In a second part of the experiment, the scientists found the participants born into the poorest families – defined as having a father from an "unskilled social occupational class" – were 43% more likely to endure multiple long-term health issues in midlife.
This is compared to those from the most privileged backgrounds, with a father from a professional class.
The participants with the most deprived childhoods were almost 3.5 times more likely to later endure mental health issues and arthritis specifically, while their risk of both impaired emotional wellbeing and high blood pressure tripled.
A low birthweight was also flagged as a risk factor, with every additional 1kg (2.2lb) in newborns linked to a 10% reduced chance of enduring multiple morbidities in middle-age.
Being overweight or obese at 10 years old was found to raise the risk, with every one point decrease in body mass index associated with a 3% reduced risk decades later.
Poor cognitive abilities at 10 years old or "emotional and conduct issues" at 16 were also linked to multiple morbidities in middle-age.
Although it is unclear why this occurs, experiencing challenges during "critical" phases of early life may affect a person's hormone levels or "internal stress", influencing their health down the line.
"Early cognitive and social disruptions may increase the risk of harmful behaviours such as smoking or alcohol consumption adopted as coping mechanisms and leading to further damage", wrote the scientists.
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"With earlier studies finding links between poor health in adulthood and lower life satisfaction, lower earnings and early retirement, public health guidance should focus on helping the population improve their health in midlife so they can age better, stay economically active and continue to lead fulfilling lives," said Dr Gondek.
Co-author Professor George Ploubidis agreed, adding: "If these links reflect causal effects, policy and practice targeting these core areas in childhood and adolescence may improve the health of future generations and alleviate potential pressures on the NHS."
The scientists have stressed their study was observational, and therefore does not prove cause and effect. Nevertheless, detailed data enabled the team to account for a range of factors that may influence the link between a person's early life and midlife health.