FDA Commissioner Margaret Hamburg has announced her resignation as head of the government agency after nearly six years at the position. In a letter sent to FDA staff, Hamburg said she intends to step down from the position at the end of March.

“As you can imagine, this decision was not easy,” Hamburg wrote. “My tenure leading this agency has been the most rewarding of my career, and that is due in no small part to all of you—the dedicated and hard-working people that make up the heart of this agency. While there is still work ahead (and there always will be), I know that I am leaving the agency well positioned to fulfill its responsibilities to the American public with great success.”

During her time with FDA, Hamburg helped modernize the country’s food safety system and took steps to help consumers make more informed, healthful food decisions. “We can honestly say that our collective efforts have improved the health, safety and quality of life of the American people,” she said.

Hamburg oversaw the development of science-based standards to create a food safety system focused on preventing foodborne illness before it occurs, rather than responding after the fact.

The Grocery Manufacturers Association commended Hamburg on her service. “Under her leadership, the agency successfully ushered in the most sweeping set of reforms to our nation’s food safety system in a generation through the implementation of the Food Safety Modernization Act [FSMA],” says Pamela Bailey, president and CEO of the association. “She was an activist commissioner in the best sense of the term: personally engaged in the important issues and always seeking the views of all stakeholders.”

Other changes to the food industry during Hamburg’s tenure include her work to reduce trans fats in processed foods; more clearly defining when baked goods, pastas and other foods can be labeled “gluten free;” updating the Nutrition Facts label; and finalizing the rules to make calorie information available on chain restaurant menus and vending machines.

“Every day, FDA employees around the world recommit themselves to the agency’s work, to quality science, to facilitating innovation and to the protection of public health,” Hamburg wrote. “And because of your dedication and your service, we have been able to achieve so many significant milestones over the past years.”

Only the second woman ever to hold the position, Hamburg became the agency’s 21st commissioner in May of 2009. She graduated from Harvard Medical School and later focused her research onthe topics of neuroscience, neuropharmacology and AIDS.

From 1991 to 1997, she served as commissioner of the New York City department of health and mental hygiene, and in 1997, she accepted the position of assistant secretary for policy and evaluation in the U.S. Department of Health and Human Services. Hamburg later served as senior scientist at the Nuclear Threat Initiative. She was also elected to membership in the Institute of Medicine in 1994, one of the youngest persons to be so honored.

 Hamburg announced Stephen Ostroff has agreed to serve as acting commissioner when she steps down. Ostroff joined FDA in 2013 and currently serves as chief scientist.