Fitness trackers and mental health apps could be doing more harm than good because they are not based on sound science, researchers have warned.
Without trials or scientific grounding, it was impossible to say whether such apps were having the intended effect, said Dr Greg Hager, a computer science professor at Johns Hopkins University in Maryland, in the United States.
"I am sure that these apps are causing problems," he told participants at an annual meeting of the American Association for the Advancement of Science in Boston.
Dr Hager cited the one-size-fits- all targets provided by some fitness trackers, such as the Fitbit, which sets users a goal of taking 10,000 steps a day.
He claimed the 10,000 steps target dated back to a 1960s Japanese study that showed there were health benefits for men who burnt at least 2,000 calories per week through exercise - roughly equivalent to 10,000 steps each day.
An early pedometer was known as the manpo-kei, which means 10,000-step meter in Japanese.
Dr Hager said: "But is that the right number for any of you? Who knows. It's just a number that's now built into the apps.
"We have an incredible number of apps being downloaded by people who may or may not understand what they are telling them or what the context for that is."
However, others suggested that the fears had been overblown.
Professor John Jakicic of the Uni- versity of Pittsburgh, whose team last year found that fitness trackers did not help people lose weight, said: "We need to be careful about relying solely on these devices."
Of far greater concern, said Mr Simon Leigh, a health economist at the University of Liverpool, were health apps that made recommendations about medication, such as adjusting insulin dosage.
"These have a huge opportunity for error," he said. "Exercise apps, on the whole, may result in a small number of incidents but, in general, they are promoting healthy behaviours. So the opportunity for damage, although increased for some, such as diabetics who suddenly up their exercise, is likely to be minimal."
Fitbit ambassador Greg Whyte, a former Olympian modern pent- athlete, said: "As 10,000 steps equates to around 8km to 9km, which will take about two hours, it is a daily target and not necessarily a single exercise-session target."
He added that over-reliance on wearable tech could be a problem.
The Fitbit website states that the 10,000-step target was designed to match the US Centres for Disease Control and Prevention's recommendation that adults should exercise for at least 150 minutes each week and notes that this target might not be suitable for those new to exercise.
The number of healthcare apps has soared in recent years, with more than 165,000 health-related apps available on the Apple store, including ones that offer to monitor blood pressure, calculate insulin doses for diabetics and encourage mindfulness exercises.
Dr Hager said: "Very few are science-based in the tradition of how we would think of doing science-based medicine."
Dr Steve Flatt, director of the Psychological Therapies Unit in Liverpool, said that while some mental health apps were well- researched and could offer benefits, the field was "in the equivalent stage of the 1860s Wild West".
He added: "People see a gravy train and are not hesitating to jump on board even if there is little or no evidence of utility, on the basis that there is a vast amount of money to be made.
"This field is in its infancy and can be likened to the snake oil salesmen of the 1860s."