Employee wellness programs have been one of the largest stakeholder groups to see the potential of wearable activity trackers -- ever since they hit the scene a few years ago. But hard data on how those trackers affect employee wellness hasn't been too common.

The Vitality Group, a US subsidiary of South Africa's Discovery Health, has released data from a three-year study of data collected directly from the 740,000 users of its incentive-based digital wellness program. The company found that involvement in an incentive-based program reduced health risk factors like high BMI, high blood pressure, poor fasting glucose levels, tobacco use, low physical activity, poor nutrition, and stress.

For users who logged fitness activities and participated in the program, their participation reduced the size of the high-risk group, based on these factors, from 27 percent of the population to 21 percent, a 22 percent reduction in the size of the group. For participants in the program who didn't log activities, the high risk group went from 38 percent to 33 percent -- a 13 percent reduction.

The Vitality Group said the findings of this study were consistent with a published study based on 300,000 adults, 192,000 of whom were in the program, which found that active users of fitness programs had hospital costs 16 percent lower than those of inactive people.

Other findings of the Vitality report were that smartphone and pedometer usage increased tremendously over the three year study period, while utilization of the gym and heart rate monitors stayed largely flat. They found that heart rate monitors were slightly more popular with men than with women (52 percent of users were men), but activity trackers were more popular with women than with men (56 percent of users were women).

Overweight or obese people were more likely to use the activity tracker, heart rate monitor, and smartphone. That population made up 67 percent of activity tracker users, 62 percent of heart rate monitor users, and 63 percent of smartphone users, although the study didn't specify what percentage of users of the program overall were overweight or obese.

For all three devices, the largest age group for use was 35- to 44-year-olds. The second largest group varied by technology, though -- 25- to 34-year-olds were the second most likely to use smartphones, while 45- to 54-year-olds were the second most likely to use pedometers or activity trackers, which also attracted more of the 55 and up crowd than the smartphone or heart rate monitor did.

Finally, the study found that step-based incentive programs did seem to have an effect on how much exercise members got, as the distribution of step counts spiked at 5,000 and 10,000 where Vitality Rewards were offered.