An estimated 10.3 million American adults have gained health coverage since Obamacare enrollment began last October, with the biggest gains among young adults and Hispanics, according to a study published on Wednesday. The findings by researchers from the Harvard School of Public Health, Brigham and Women's Hospital in Boston and the federal government are based on data pointing to a 5.2 percentage point drop in the U.S. uninsured rate since last September for Americans aged 18-64. The study, which appeared in the New England Journal of Medicine, also found evidence that more Americans had a personal doctor and fewer difficulties paying for medical care within the first six months of gaining insurance. The law known as Obamacare, President Barack Obama's signature domestic policy achievement, provides federally subsidized private coverage through new online insurance marketplaces and an expansion of Medicaid in 26 states and Washington, D.C. The U.S. Department of Health and Human Services said in May that more than 8 million Americans signed up for private plans through new online insurance marketplaces during a six-month open enrollment period.