Runners and others aspiring to healthy lifestyles who use fitness-monitoring devices to track steps per day, calories burned and similar data should be aware their information can be sold to third parties, Sen. Charles Schumer said Sunday.

Fitbit, which Schumer called "one of the most well-known" devices, and similar others can violate users' privacy, he said at a news conference in Central Park as joggers and walkers streamed behind him.

"Personal Fitbit bracelets and the data they collect on your health, your sleep, your location should be just that -- personal -- not sold to a wide variety of other users," said Schumer (D-N.Y.).

The devices track and store data on location, sleep patterns and sometimes even weight and blood pressure, he said. That data can be shared with insurance companies, mortgage lenders, employers and others, he said.

Schumer called on the Federal Trade Commission to alert fitness device users that their data can be sold and allow them to immediately opt out.

Fitbit in a statement Sunday said it does not sell data.

"Our privacy policy prevents us from doing this," the San Francisco-based company said. "We are committed to our users' privacy and welcome the opportunity to work with Senator Schumer on this important issue."

Fitbit said it does not share personal data unless a user specifically directs it to do so.

An FTC spokesman declined to comment on Schumer’s concerns.

Mobile medical applications -- meant to diagnose, treat and cure diseases -- are regulated through the Health Insurance Portability and Accountability Act, or HIPAA, Schumer said. Wearable fitness devices are not as regulated, he said.

"The kind of privacy laws that should protect us have not caught up to the new technology that helps keep us healthy," he said.