Nearly 870,000 Californians have signed up for an insurance policy through the state's health care exchange, as the state intensifies efforts to boost participation ahead of the March 31 enrollment deadline. Those are the latest numbers from the U.S. Department of Health and Human Services. 

California leads the nation in enrollment, accounting for roughly 20 percent of all sign-ups across the country. Nationally, about 4.2 million people have enrolled in individual insurance plans under President Barack Obama's health care reforms. The law also allowed states to expand Medicaid, which provides health insurance to lower-income people. In California, an additional 850,000 people have been determined to be eligible.