Almost one-third of US smartphone owners, which is about 46 million unique people, used apps from the fitness and health category in January 2014, according to a report from Nielsen's Mobile NetView 3.0 software, which is on-device software installed onto iOS and Android smartphones with permission from survey participants. Approximately 5,000 panelists aged 18 and over participated in this report.

The 46 million users accessed the apps, on average, 16 times per month and used for close to an hour.

The number of smartphone users that accessed fitness apps in January 2014 jumped 18 percent year over year. Nielsen said popular apps that connect to wearable devices include Fitbit's app, which has 3.3 million users, and Nike+Running, which has 0.8 million users. Nielsen also included Samsung’s S Health app, which has 3 million users, in this category although when the survey was conducted in January, before Gear Fit launched, there were no wearable devices that connected with the S Health app in the US.

The most popular standalone wellness apps used in January 2014, which Nielsen said varied based on the consumer's wellness goals, were Calorie Counter & Diet Tracker by MyFitnessPal, which had 8.7 million users, Nexercise, which had 3 million users and Runkeeper, which had 2.1 million users that month, according to the research firm.. While Nielsen pointed out in its last survey that half of wearable owners were in the 18 to 34 age range, the majority of consumers using MyFitnessPal are over the age of 35.

Additionally, more women than men are using wellness apps. Forty four percent of people aged 30 to 39 use health apps and 60 percent of that group consists of women. The last survey also showed that men and women were equally likely to own wearable devices, but this report found women used Fitbit’s app 29 times per month, while men used the app 16 times per month. As this survey noted that more women use apps than men and more men use dedicated devices, that might explain the larger percent of women using Fitbit's app. The month this data was recorded, January 2014, Fitbit released a passive tracking feature on its app so that the app could be used independently of the device.

Last week, another survey, this one of 471 people, from Nielsen found that only 15 percent of consumers use a nutrition-tracking website or mobile app to stay healthy. Additionally, 13 percent of consumers use a fitness game on a mobile devices or game console to stay in shape. Social interaction is a big motivator for consumers who want to get healthy — 49 percent of respondents said their family and friends were the most helpful for staying motivated. This could explain why the social aspect of health programs such as Weight Watchers are more popular than other features.