Millennials may not be as healthy as they think they are and may be worse off than Generation X was when they were their age, a new report found.

More than eight in 10 millennials said they considered themselves to be in good or excellent health, but the prevalence of the top 10 health conditions affecting their generation increased from 2014 to 2017, a report released Wednesday by the Blue Cross Blue Shield Association says.

The report analyzed the data of 55 million commercially insured millennials, defined as those ages 21 to 36 in 2017, and identified the top 10 conditions affecting their health.

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Although the data showed the millennials were living at 95% of their optimal health, the research found that nearly all of the top 10 health conditions increased over the three-year period. The data was based on an index that scored their potential lifespan in the absence of disability and premature death.

Among the conditions, major depression increased by 31%, disorders tied to hyperactivity by 29% and Type II diabetes by 22%.

When compared to members of Generation X – those born in the early 1960s to the early 1980s – at the same age in 2014, the report found older millennials, ages 34 to 36 in 2017, had a higher prevalence of nearly every condition.

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How quickly the prevalence of most of the conditions increased among millennials was also greater than Generation X, said Brian Harvey, executive director of Blue Cross' Health of America initiative.

For example, depression rates rose just 16% for Gen X and 14% for baby boomers, compared with the 31% increase for millennials.

Within the top 10 conditions affecting millennials, six were tied to behavioral health, a finding that Dr. Vincent Nelson said was particularly concerning.

While greater awareness around mental health issues may lead to millennials going to a health care provider to treat an issue such as depression, other factors like growing feelings of isolation in the digital age and better diagnoses of these conditions may be causing rising rates in millennials, said Nelson, the vice president of medical affairs at the Blue Cross Blue Shield Association.

"There needs to be increased access to care to treat these conditions and more providers in behavioral health," Nelson added.

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Dr. William B. Leasure, a psychiatrist at the Mayo Clinic and chair of its integrated behavioral health department, said affordable access to mental health treatment beyond traditional, face-to-face appointments is needed, too.

"There are not enough mental health providers to cover the entire population ... we can't do that all ourselves," he said. "We need to involve other resources and primary care providers."

Another concerning trend in the report: Almost a third of millennials didn't have a primary care physician.

A 2018 poll by the Kaiser Family Foundation similarly found 45% of people ages 18 to 29 had no primary care provider, whereas 28% of those 30 to 49, 18% of those 50 to 64 and 12% age 65 and older did.

Many millennials may go to a doctor only when they have a specific condition they think needs to be treated, rather than for routine physicals, Nelson said. Because the Blue Cross report looked only at insured millennials, cost was likely not as big of a factor, he said.

"A lot has to do with thinking that 'I am young and healthy and don't need to go,'" Nelson said.

"Primary care providers are key for early identification of mental health disorders and early treatment of them," Leasure said. By having a primary care physician screen for something like depression, treatment can begin even before a patient needs to make an appointment with a specialist, he said.

Many of these conditions intersect, too, furthering the need for primary care. For example, rates of depression are higher in individuals with Type II diabetes and going to a primary care doctor can make identifying and treating both easier, Leasure said.

While millennials do still use health care services other than primary care doctors, such as emergency room and urgent care visits, they're not getting the care of a consistent provider who can spot trends in their health, Harvey said.

"Because medical records may not synchronize, no one picks up on the fact that say you've come in four times this year with elevated blood pressure," Harvey said. "Then that doesn't get treated" in the same way a primary care doctor could.

Follow USA TODAY's Ryan Miller on Twitter @RyanW_Miller