Life insurance company John Hancock made a splash last week with the news that soon all of its policies would come bundled with the option to let the company track your fitness — via either a website and app, or through the use of a fitness tracker such as Apple Watch or Fitbit.

The move underscores how fitness tracker data is an as-yet untapped gold mine for businesses — particularly the insurance industry, whose financial bottom line directly depends on the health of their customers. John Hancock isn’t particularly shy about this: “The longer people live, the more money we make,” as the company’s CEO Brooks Tingle told the New York Times.

The published research on Fitbits and similar devices, however, has yet to uncover a clear link between fitness tracking and fitness, to say nothing of longevity and mortality, or of insurance companies’ profits. But there is some evidence that if the use of the devices is paired with incentives — rewards, challenges and leaderboards (“gamified,” in social science parlance) — people can see real health benefits.

The big question: Will potential insurance customers buy it?

Since fitness trackers are attached to your body, they’re capable of providing a real-time fire hose of data on the most intimate aspects of your existence — where you go, when you sleep, how much you weigh, how fast your heart is beating, and so on. Athletes and people interested in maintaining or increasing their fitness are naturally interested in this data, and the numbers are fun to track over time for anyone with even a passing interest in what makes their bodies tick.

Devices such as the Fitbit are predicated on the idea that tracking these numbers is the first step toward improving them: “Know yourself to improve yourself,” as the company’s homepage puts it. But researchers who’ve studied how these devices are actually used in the real world have found that it’s not quite that simple.

One randomized controlled trial based in Singapore, one of the largest such studies on fitness trackers done to date, found in 2016 “no evidence of improvements in health outcomes” relative to a control group, among people who were randomly assigned to use a Fitbit. A similar study published in the Journal of the American Medical Association in 2016 found that among 470 overweight young adults, people randomly assigned a fitness tracker actually lost slightly less weight over a two-year period than the group that did not receive a tracker.

These studies come with some caveats, including the fact that the actual trials involved were carried out from 2010 to 2014, using early-generation fitness trackers that lacked many of the bells and whistles of today’s models. Newer models have a whole suite of incentives designed to get people using their devices more, and hence increasing their activity levels.

Fitbit, for instance, offers badges for achievements, like walking 20,000 steps in one day or climbing the equivalent of 100 floors. They have leaderboards, where users can compete against friends, family and strangers to see who can crank the most steps or miles out of a day or month. The devices can be set up to nudge users with reminders when they’re a few hundred steps behind a given goal for a day.

A study published earlier this year in the Journal of the American Heart Association found that among sedentary office workers, Fitbits used in conjunction with office-wide leaderboards and challenges were more effective at getting workers out of their seats than Fitbits alone. A separate study published in JAMA Internal Medicine this year found that people who used a service that gamified their Fitbits, offering them points for goals hit and a level progression with increased fitness, hit their daily step targets significantly more often than users who didn’t have such elements.

John Hancock’s new insurance program, which it calls Vitality, incorporates many of these gamelike elements. The big one is this: The more active people are, the more their insurance premiums go down, up to a savings of 15 percent on annual premium costs, or $300 a year for a typical term life insurance policyholder. Other rewards for hitting fitness targets include Amazon gift cards and retailer discounts, as well as massive discounts on Apple Watches.

There are, of course, privacy concerns whenever you give a third party access to your data, especially medical data. And there’s concern that in the long run, people who are disinclined to share fitness data may face difficulties like increased rates or even being cut off from insurance coverage completely. Those latter concerns are in part what prompted the state of West Virginia to scrap a plan that would have required state employees to wear fitness trackers or face a penalty of higher premiums and deductibles.

Part of these concerns may simply be a function of semantics — the John Hancock plan is framed as a benefit for people who opt in to tracking, while the West Virginia plan penalized people who opted out. When it comes to companies’ bottom lines and consumers’ pocketbooks, there may not be much difference between the two approaches. And on the privacy front, insurers already have mountains of data on you: your name, address, Social Security number, payment information, and in many cases medical records.

In the long run, there may be real benefits for consumers willing to share their fitness data with insurers, particularly if the practice spreads to health insurance providers, as seems inevitable at this point. People who track their fitness may end up in better health and receive cheaper insurance relative to those who do not. Insurance companies may make more money off healthier clientele.

It’s a win-win for everyone, except for the people who decide not to share their fitness data with their insurers.