Millennial women who grew up reading JK Rowling’s wizard series are driving sales in other genres as they reach their 20s and 30s, according to recent research

The women switched on to books by Harry Potter are shaping the literary world, according to new research, boosting the market in thrillers, adult colouring books and clean eating.

Statistics from Nielsen Book show that fiction sales were up 5.2% last year, with crime and thriller novels accounting for 29% of the market, the second-largest genre behind general and literary fiction, which was worth 41%. The crime sector is estimated to have increased last year to a record volume of over 25m copies sold – including ebooks – with psychological thrillers such as The Girl on the Train, called “grip lit” by the book sales monitor, helping drive the growth.

Nielsen said that 67% of grip lit is bought by women, with 25 to 34-year-olds accounting for the largest age category within that. Women accounted for 60% of the sales for Paula Hawkins’ smash hit The Girl on the Train, with the same age range dominating sales. Just 17% of sales of the novel were to males aged 25 to 34.

According to Bookbrunch editor Neill Denny, these trends show the influence of a “Harry Potter cohort”, pointing out that a 12-year-old who read JK Rowling’s first novel in 1997 will become 31 in 2016. “A generation of women in their 20s and early 30s, who grew up reading Harry Potter, are now energising the book trade,” he wrote.

For Jo Henry at Nielsen Book, the female millennial’s book-buying power has shaped publishing over recent years, with strong sales for young adult books such as Divergence and the Hunger Games fuelled by young women over the age of 18 as well as by children.

“It is Generation Potter … Two years ago they were reading YA, now they’re coming on to grip lit – it’s the same cohort,” said Henry. “I think it’s a generation we have to keep an eye on – they’re obviously really heavy book readers, and we have to make sure we’re reaching them in the right way. They have huge spending power, and this will only increase.”

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“It’s wonderful to see that the Harry Potter generation – both male and female – have not fallen out of love with books,” said Waterstones buying director Kate Skipper. “Thriller sales are booming on the back of titles such as The Girl on the Train, Disclaimer and Black-Eyed Susans selling brilliantly and appealing across the genders.”

Samantha Eades, who is nearly 31 and an editor at new Orion imprint Trapeze, signed up to the label with enthusiasm.

“As a teen I crossed my fingers each night,” she said, “hoping for a letter for Hogwarts to be delivered and in my 20s I queued up for the final midnight signing with a lightning bolt on my forehead.” Eades may still imagine herself a Gryffindor, but her taste in fiction has definitely moved on. “I, like many women in their 20s and 30s, am completely addicted to grip lit,” she continued, citing titles including The Girl in the Red Coat, Disclaimer, In A Dark, Dark Wood and I Let You Go, as well as The Girl on the Train.

“Unreliable narrators like Rachel from The Girl on the Train, Amy from Gone Girl and Clare from In A Dark, Dark Wood are our new Ron, Harry and Hermione, with bad husbands, jealous best friends and dangerous next-door-neighbours our new He Who Must Not Be Named,” Eades said. “For me, what defines ‘grip lit’ is emotional storytelling with a compulsive pull – we as the reader just can’t turn the pages fast enough.”

In a new white paper on millennial females, Brands Risk Losing the Women of Tomorrow, Nielsen revealed that millennials are also more comfortable than other age-groups with self-published writing. With these books now accounting for more than one-in-five ebooks purchased, it said that “more than a third of millennials agree that self-published authors write books they like”, a level of agreement “significantly higher than for other age groups”.

The Potter generation of female readers are also driving growth in non-fiction, according to Nielsen’s data, with health and dieting sales up 61% in value last year thanks to strong sales of clean-eating titles such as Deliciously Ella. Females account for 68% of sales in the genre, with 25 to 34-year-olds the largest age category, said Nielsen, which drew its data from Nielsen BookScan, Nielsen PubTrack Digital and Nielsen Books and Consumers.

But the biggest area for growth in non-fiction was revealed to be adult colouring books, with the arts and craft sector up 160% in 2015 thanks to titles such as Millie Marotta’s Animal Kingdom, which has sold almost 470,000 copies to date, and the Harry Potter Colouring Book, which counted sales of 263,000 copies in just nine weeks.

“In the book market, the biggest driver of growth in 2015 came from mindfulness books,” said the new Nielsen white paper. “These books fill a need for pleasure and relaxation. Seven-in-10 adult colouring books sold were for females – and of these, the biggest users were millennials (31%).”

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According to Waterstones’ Kate Skipper, the colouring trend is set to continue this year.

“One of the reasons it has proved so resilient is that there is such a diverse range of titles, which appeal across a wonderfully broad customer base,” she said. “Bestsellers such as the Harry Potter Colouring Book, the Mindfulness Colouring Book and the Tattoo Colouring Book all appeal to distinct sections of the market, whereas titles from Joanna Basford and Millie Marotta have a much wider appeal and have driven enormous sales accordingly.”

In total, book volume sales for 2015 were up by 3.7% compared to 2014, and 6.6% by value, said Nielsen, which is due to discuss the book buying power of the female millennial at a conference on 23 March.