SEATTLE (AP) – The Bill & Melinda Gates Foundation says its CEO is stepping down after more than five years in the role.

The Seattle Times reports that Dr. Susan  Desmond-Hellman, 62, was the third CEO in the organization’s 20-year history.

With a background as a research scientist and physician, she was the first to come from outside Microsoft.

She cited family and health as reasons for leaving the world’s richest philanthropy, calling it “the toughest decision” of her career.

The foundation said Thursday that president of global policy and advocacy and chief strategy officer, Mark Suzman, will become CEO in February.