One of this year’s most popular Christmas presents looks like being a device that purports to help reverse the effects of festive overindulgence – the fitness tracker.

Sales of the distinctive wristbands – which monitor the number of steps taken, calories burnt, heart rate and quality of sleep among other things – have soared and the signs from retailers are that they will jostle for attention with, or perhaps displace, the traditional boxes of chocolates and bottles of whisky under the tree.

John Lewis has already sold four times as many Fitbits, one of many brands in the tracking market, compared with last year; and on Black Friday last week the increase over 2014’s sales extravaganza was 1,200%. Harry Boughton, the store’s buyer for tablets, computing and wearable technology, put the surge down to “increasingly health-conscious” consumers and said it is expected to last into the new year.

With obesity rising, fitness trackers represent an attempt to harness modern technology – often seen as a contributor to sedentary lifestyles – to get people taking better care of themselves (and obviously make money for the manufacturer).

Fitbit says its mission is to “design products and experiences that fit seamlessly into your life so you can achieve your health and fitness goals, whatever they may be”. One of its many competitors, Jawbone, says: “There’s a better version of you out there. Get UP [its patented technology] and find it.”

The messages appear to be hitting home. The number of people using health and fitness wearables is predicted to rise to 100 million in 2018, compared with 15 million in 2013, while global revenues from fitness trackers are expected to increase from over $2bn (£1.3bn) last year to $5.4bn by 2019.

Iltifat Husain, editor of iMedicalApps.com and assistant professor of emergency medicine at Wake Forest School of Medicine in North Carolina, went some way to explaining the popularity of fitness trackers and similar apps in the BMJ in April. He argued that people “tend to carry their smartphones with them everywhere they go, and it’s much easier to track weight loss and calories in one place on your phone than on pieces of paper”.

Referring specifically to Fitbit and Jawbone, he said: “There is no current evidence that these fitness devices improve outcomes or exercise compliance; likewise, there is no evidence that they cause harm.”

Responding to the trend, NHS England has raised the possibility of fitness apps being prescribed by creating its own apps library of health issues. “We hope, by giving them our official backing, we will give clinicians, citizens and carers the confidence to use them,” said NHS England’s national director of patients and information, Tim Kelsey.

But some healthcare professionals have concerns about the trend for self-monitoring. Dr Aseem Malhotra, a London-based cardiologist and anti-obesity campaigner, said a healthy friend contacted him when he became concerned after a fitness tracker he was using showed his heart rate was high during exercise, even though this is perfectly normal.

“I think it is how they are used,” said Malhotra. “There’s an issue about these apps creating anxiety so that people get referred to doctors or cardiologists like me. There’s misinformation about health through technology that we need to be aware about. Overdiagnosis and overtreatment is one of the biggest threats to modern healthcare, not just financially but to health. We don’t have time to look after the worried well.”

His last point alludes to the fact that while fitness trackers may seem to be a useful tool in the fight against obesity, they typically cost between £40 to £150, which may place them out of reach of some who might benefit, particularly as obesity tends to be higher in deprived areas.

Despite concerns about how they are used, in the US fitness trackers have been adopted by employers to try to improve employees’ health – corporate sales are one of the fastest growing parts of Fitbit’s business – and at least one insurance company has offered a discount to people who allow it to monitor their trackers. It is yet to happen in the UK, but Malcolm Tarling, a spokesman at the Association of British Insurers, said this could change “when the health benefits become better established”.

Employers and insurers having access to data and the fact that some devices automatically post information to social media, such as the route a user has just run – ostensibly a way of sharing goals and achievements – bring with them other issues.

Big Brother Watch chief executive Renate Samson described a fitness tracker as “a bit of surveillance on your wrist” that contains “your entire life”. She said: “There are obviously benefits to these things, but the most important thing for all of us is we look at the terms and conditions, opt in or out of things. Don’t just go with what the factory settings are, make the changes.”

Beyond the health and privacy issues, there are more prosaic concerns. Last year, consulting firm Endeavour Partners suggested that about a third of owners of “smart wearables” ditch their devices within six months of purchasing them, suggesting they may ultimately go the way of many a present eagerly unwrapped on Christmas Day, only to be ultimately abandoned.