Facebook CEO Mark Zuckerberg said Wednesday that the changes the company made to its service last year reduced time spent on the site by 50 million hours per day, or 5 percent.

"Already last quarter, we made changes to show fewer viral videos to make sure people's time is well spent. In total, we made changes that reduced time spent on Facebook by roughly 50 million hours every day. By focusing on meaningful connections, our community and business will be stronger over the long term," Zuckerberg wrote.

On a conference call with analysts, Zuckerberg said that figure represented 5 percent of the total.

The company has also begun to make changes to its content-recommendation software amid criticism that Facebook has been used to spread misinformation, hate speech and other violent content.

Last April, a Facebook user recorded and uploaded a video of himself killing an elderly man.

On the company's previous earnings call in November, Zuckerberg had said: "I want to be clear about what our priority is. Protecting our community is more important than maximizing our profits."

The decrease in time spent could likely cause the company to insert more ads into the NewsFeed to keep ad prices consistent, said Omnicom's Hearts & Science executive director of digital activation Ben Hovaness.

Facebook's advertising sold through an auction forces, which means price is related to demand. As user time decreases, ad inventory in the NewsFeed will also decrease. Immediately, it will cause ad prices to go up so Facebook will have to balance the issue out by adding more ads.

"Facebook will have to increase ad load to keep costs stable," Hovaness said.

Zuckerberg made the comments as part of the company's fourth-quarter earnings announcement.

Facebook reported sales that topped analysts' expectations. Its profit was less than expected due to a huge increase in its tax bill caused by recent tax-law changes.

CNBC reporter Michelle Castillo contributed to this report.