Regina Benjamin, the nation’s 18th surgeon general, announced she was stepping down today in a letter to officers and friends of the U.S. Public Heath Commissioned Corps.

Upon assuming office four years ago, Benjamin said her goal was to create a movement “to change our health care system from one focused on sickness and disease to a system focused on wellness and prevention. With your help,” she wrote, “that movement has begun.”

Benjamin chaired the National Prevention Council, created under the Affordable Care Act, and led the release of the National Prevention Strategy, the first-ever blueprint to guide U.S. efforts to the most effective and achievable means for improving health and well-being.

“The [prevention strategy] illuminates and puts into action what we in public health have been saying for more than a hundred years,” she wrote. “Prevention is the foundation of public health and prevention is the foundation of an effective health care system.”

“She has been a remarkable advocate in promoting the value of prevention as a national health priority,” said APHA Executive Director Georges Benjamin. “We are extraordinarily grateful for her strong public health leadership.”

During her tenure, the Office of the Surgeon General released a number of reports and calls to action on a range of topics, including breastfeeding, preventing tobacco use among youth and how tobacco smoke causes disease.

“She continued the long tradition of surgeons general serving as a major advocate for reducing tobacco use,” said APHA’s Benjamin.

She was particularly visible leading surgeon general walks through her “Every Body Walk” campaign, which asked Americans to walk for 30 minutes a day, five days a week to promote health and prevent disease.

“Regina Benjamin taught America how to walk again,” said Benjamin of APHA. “She elevated walking as a simple yet important form of physical activity available to most Americans. Through her walks, she brought communities together and worked to make being healthy fun again.”

Benjamin will leave the position effective July 16. Boris Lushniak, her deputy, will serve as acting surgeon general while a replacement search is underway.