After five years in the role, Dr. Susan Desmond-Hellmann announced she is stepping down from her position as CEO of the Bill & Melinda Gates Foundation, the multi-billion dollar nonprofit created by the Microsoft founder’s wife.

“One of my mantras is ‘take your own pulse first,” Desmond said. “Over the last few months, I’ve done just that and concluded that I need to slow down.”

Desmond-Hellmann, 62, was the first CEO to come from outside of Microsoft, and before becoming a part of the world’s wealthiest philanthropic effort she was a physician and research scientist. In a tweet announcing her departure Thursday, Desmond-Hellmann said it was “the toughest decision” of her storied career.

She is leaving to focus on her health and family, and she noted one of her own philosophies for the decision in the tweet.

“One of my mantras is ‘take your own pulse first,” Desmond said. “Over the last few months, I’ve done just that and concluded that I need to slow down.”

Desmond-Hellmann’s accomplishments while running the Gates Foundation are numerous. She helped establish the Gates Median Research Institute, worked to implement the foundation’s first substantial investment in ending poverty in the U.S. and she helped donate a record-breaking grant for health research to the University of Washington.

Melinda Gates, founder of the foundation that has been around for 20 years, praised Desmond-Hellmann’s accomplishments in a statement.

“Sue brought an incredible set of attributes to the foundation: scientific expertise, tested leadership skills, a passion for building a strong internal culture, and, above all, a dedication to the mission of making the world a healthier, more equal place,” Gates wrote in the statement, according to the Seattle Times.

Mark Suzman, the foundation’s chief strategy officer and president of global policy, will take over as CEO after Desmond-Hellmann’s departure. Suzman’s tenure with the foundation goes back to 2007, and before that he held multiple positions at the United Nations.