More millennials in the U.S. are suffering from chronic health problems, potentially restraining the lifetime economic potential of a generation of young adults. A spike in conditions like depression, hypertension and high cholesterol among younger people could increase health-care costs and lower incomes in coming years, according to a report Wednesday from the Blue Cross Blue Shield Association, a federation of 36 independent companies that together provide coverage for 1 in 3 Americans. Between 2014 and 2017, rates of depression among millennials surged by 31%, while hyperactivity rose 29% and hypertension increased 16%, according to the report.