Healthcare Q&A site Sharecare is buying RealAge from Hearst for an undisclosed sum, the companies said.

The deal gives two-year-old Sharecare a big bump to its user numbers, a base on the West Coast and a new front door that’s drawn throngs into RealAge over the years. The combined company will have around 16-17 million active users, said Sharecare, and around 8 million by Comscore’s estimation, vaulting it to the Number 8 position among healthcare portals by the online metrics firm’s reckoning.

RealAge’s Test, which has been taken by 29 million people since it launched in 1999, will be incorporated into Sharecare’s site registration. The test teases out information on registrants’ lifestyle habits and medical history to determine their “RealAge.” The firm brings a substantial user base to Sharecare – RealAge boasts 4 million monthly unique users, and the site has current emails for around 15 million who have visited within the past year — along with consumer behavioral expertise gleaned from all those tests, drawing on a database containing 4 billion health facts.

“We always thought RealAge would make a great product inside Sharecare,” said Sharecare founder Jeff Arnold, “we would turn that universal metric of one’s body age into how you would register for our site. And then what’s exciting about it is, because Sharecare’s already a recommendation engine, we’re going to be able to match people who’ve taken the test to doctors, or programs like Transformation Nation, or hospitals, or weight loss programs and other things – marry their data with our recommendation engine and not just deliver tips but introduce consumers to the appropriate providers and programs.”

Sharecare bought The Little Blue Book, a doctor directory, in January, and will use it to match users to local physicians.

“The way RealAge works today you take the test and then you start to get tips to reverse your body age, and we’re going to use that as a social platform instead of an email marketing platform,” said Arnold. “We’ll continue to send it to your inbox but we’ll also send it onto your profile page, which is all socially enabled. And when you get that health tip, it’s going to have other recommendations, like doctors in your area, trainers in your area that are on Sharecare.”

Sharecare will maintain RealAge’s San Diego headquarters as its West Coast office and no layoffs are planned. RealAge has 60-some employees, and the two firms combined will boast a headcount of around 170.

Hearst retains an equity interest in the company and Hearst Entertainment & Syndication president Scott Sassa will join Sharecare’s Board of Directors.

Sharecare, the brainchild of Arnold and Dr. Mehmet Oz, launched in 2010 with backing from Oprah Winfrey and the Discovery Channel, and more recently has attracted investments from Google’s Eric Schmidt and Galen Partners, a big healthcare private equity firm. The firm hasn’t yet turned a profit, and could soon but won’t, despite adding its “slightly bigger” revenues to RealAge’s, pending some major investments, said Arnold, including an “interactive medicine cabinet,” a sort of medical iTunes for health apps.