The email, which was sent on Wednesday, was a response to President Barack Obama's plan to cut Social Security benefits. Warren said she was "shocked to hear" of Obama's plan before describing how her brother David lives on the $13,200 per year he receives in Social Security benefits.
A reporter from Boston's FOX 25 questioned Warren on the email, asking the senator why she didn't help her brother.
"I do help him. This is a question about how much," Warren said. "He was worked for 40 years and paid into this system and that's all the money he has to live on. And there are literally millions of people around the country for whom that is the case."
Warren also emphasized that the email was not just about her brother, but about all Americans who rely on Social Security benefits to get by.
"Let's be clear about this. Not everyone has a sister who can help," Warren said. "This is about people who work all their lives and all they've got at the end is their social security."
Warren's not the only one to criticize Obama's plan, which involves a measure of inflation known as the chained Consumer Price Index, or chained CPI. Sen. Bernie Sanders (I-Vt.) said Obama "owns" chained CPI, and Grover Norquist, leader of Americans for Tax Reform, called it "a Taxpayer Protection Pledge violation."