Research conducted for the Financial Times by Evidon, a web analytic and privacy group, has found that the top 20 most popular health and wellness apps forward user data to “a web of nearly 70 companies”.

The third party firms, which are in mainly analytics and advertising, use the data to build user profiles or develop personalised marketing campaigns.

Data privacy is viewed as an increasingly important concern for mobile health and wellness apps.

Among the apps surveyed were WebMD, MapMyFitness and iPeriod.

However, several developers, including WedMD, argued that data about their users is anonymised and is not sold.

The app firms also said that the data is generally used for advertising and analysis on their own apps, among other uses.

WebMD said it stopped third parties from linking consumer data about its users with other profile information, or using it outside the company’s site.

Scott Mayer (pictured), CEO of Evidon said: “If there is a lot of content that is being provided to you for free, data is driving the economy of that content.”