More than 40 million smartphone owners in the U.S. actively use at least one wellness or fitness tracking app, according to a survey by international market research firm Parks Associates, which interviewed 10,000 consumers who live in a household with a broadband internet connection in Q4 2014.

Weight loss, tracking daily activity and nutrition are the most common uses for consumers, says Harry Wang, director of health and mobile product research at Parks Associates. Within those categories running apps, Yoga instruction, bike tracking, stress reduction, sleep monitoring and medication reminder apps are the most popular, Wang says.

In the past, consumers could look at labels to determine the number of calories they consumed or see how many they burned on a machine at the gym, but all the information was not stored in one location, like it can be in an app, Wang says.

“It was piece-by-piece data and (it was hard to) connect the dots for how to improve,” he says.

Most smartphones are now equipped with accelerometers, which detects acceleration, and altimeters, which can detect, for example, if someone is going upstairs, Wang says. Beyond helping consumers track their fitness these features also help stores and brand better target shoppers. For example, the feature could enable a department store, for instance, to send promotions to a shopper based on what floor she’s on. “The sensors in smartphones are pretty robust,” he says.

Another common type of apps are food diaries that lets a consumer record the food she ate and assign a caloric value to it. Many such apps take into account if the item was cooked at home or in a restaurant when assigning a value to it.

“These tools combined together provide a good energy map for people throughout the day and help them to understand the best way to achieving a weight loss goal or healthy living goals,” Wang says.

The helpful information in such apps is attracting significant downloads. For example, the MyFitnessPal health app has 80 million users, Wang says.

Wearable devices, such as Fitbit or Jawbone, also factor into the number of consumers using wellness apps, as many wearables track daily activity and can be further monitored in an app. Fitbit has between 5 and 10 million downloads on Google Play and Jawbone says it has millions of users, but declines to provide an exact number.

As the market for wearables grows, so will health and fitness apps, says Joe Laszlo, senior director, mobile marketing, at the Interactive Advertising Bureau.

In a separate survey section in the Parks study of about 4,000 smartphone owners who live in a home with broadband internet, 52% say they don’t have a fitness tracking device nor do they use a fitness app. 16.9% own a web-connected fitness tracking device and use a fitness app. 16.1% own a connected fitness device but do not use a fitness tracking app. And 15% do not own a fitness tracking device but use a fitness tracking app.

While smartphones have become more sophisticated in their technology, wearables are more accurate for tracking physical activity, Wang says. If a smartphone is in a pocket, the sensors on the phone don’t monitor activity as well as a wearable device on the person’s wrist, leg or other part of her body.

“A wearable is a better device for a more serious user,” Wang says.