Almost half of women aged between 35 and 44 (48 per cent) have bought trainers in the past year, compared to 30 per cent who have bought new heels.
The research by consumer analysts Mintel confirmed that 2016 is the first time more women have bought new trainers than high heels.
And experts say mature celebrities such as former Spice Girl Victoria, 42, are thought to be influencing sneaker sales.
Previously, trainers and high heels sales matched, with 35 per cent of women buying new heels and trainers in 2015.
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Overall, flat shoes are still the most popular type of shoes purchased, at 51 per cent.
The research showed 30 per cent bought flat boots, while 25 per cent bought flat sandals came.
And sales of heels look set to fall flat, as 59 per cent of women said they preferred to buy flat shoes, compared to just 12 per cent who would rather don heels.
And that could be down to a desire for comfort over style, as three-quarters (74 per cent) who bought shoes last year said feeling comfortable was more important than fashion.
And 39 per cent said they opted for sporty or casual styles of shoes, compared to just one in five (21 per cent) who preferred formal styles of shoes.
Tamara Sender, senior fashion analyst at Mintel, said: "For the first time ever sales of trainers have overtaken high heels.
"The UK sportswear market has seen strong growth in the last year, and there has been a trend for consumers to integrate sports clothing into their daily wardrobes, meaning trainers have also become more popular among women, overtaking heels to become the second favourite item of footwear after flat shoes.
"Athletic footwear is increasingly being used for everyday non-sporting activities, showing that trainers are now more likely to be used for non-sports use.
"Women aged 35 to 44 have become the main trainer buyers, proving the trend is no longer limited to younger consumers."