With the future of US healthcare likely to rest on the next presidency, a new study from Psychology, Health & Medicine highlights just how complex the medical needs of many Americans now are.

As the authors of the study, Elizabeth Lee Reisinger Walker and Benjamin G. Druss, observe: "The health of individuals in the U.S.A. is increasingly being defined by complexity and multimorbidity, the co-occurrence of two or more chronic medical conditions."

Given the medical and socio-economic difficulties often faced by people with mental illness, and the lack of research into the other medical conditions they might suffer from, the authors set out to discover, using publicly available data, what proportion of US adults experience each combination of mental illness, substance abuse/dependence and chronic mental conditions. They also investigated how those combinations of conditions were related to poverty.

They found that overall, 18.4% of adults had a mental illness in the past year, and 8.6% reported substance abuse/dependence during the same time. Nearly 40% had one or more chronic medical conditions in their lifetimes, and 14.7% were living in poverty.

Compared to individuals without any condition, adults with one condition (any mental illness [AMI], substance abuse/dependence or chronic conditions) reported higher percentages of living in poverty, receiving government assistance, having less than a high-school education, being unemployed, and having no health insurance.

When looked at together, 6.4% of individuals reported AMI and chronic conditions, 2.2% reported AMI and substance abuse/dependence, 1.5% reported substance abuse/dependence and chronic medical conditions, and 1.2% -- equivalent to 2.2 million people -- reported all three conditions.

The association between mental illness and substance abuse is also laid bare by the study: people with AMI were over three times more likely to report substance abuse/dependence, almost 1.5 times more likely to have a chronic medical condition, and 1.2 times more likely to live in poverty.

As Elizabeth Lee Reisinger Walker commented on the research last week: "Just over half of adults in the US have one or more chronic condition, mental disorder, or dependence on substances. These conditions commonly overlap with each other and with poverty, which contributes to poor health."

The pair conclude that improving the health of people with multimorbidities will involve increased access to and coordination between a variety of services. As they observe: "Collaborative care models are effective in treating mental illnesses in primary care and providing primary care in specialty mental health settings."

Walker concludes: "In order to promote overall health, it is important to consider all of a person's health conditions along with poverty and other social factors."

But what the future holds for the 50% of Americans suffering from multiple health challenges remains to be seen.