There had to be one...DD took five, including maths, physics, chemistry and biology.
I don't think having more than three helped her much in getting a place. It might have done if she had sat BMAT which seems to test a wider science knowledge, or had applied to Barts/Royal London which scores 4 A levels. But generally as long as her academics were at the level required, it was UKCAT, PS, shadowing/volunteering, and interview performance that mattered.
It also meant a horrid log jam in March with three interviews and three sets of coursework deadlines.
Keeping up a broad range does mean that she has more scope to intercalate in an area that interests her (medical engineering) and it meant she had a bit more leeway when it came to the exams themselves as her offer was only based on three A levels. (Just as well as she picked up a bug before her physics A level and was very unwell when she sat it. She did OK but would have been petrified if she felt her med school place were dependent on her performance that day.) Oddly she started A levels liking chemistry and biology, but by the end would probably have claimed to prefer maths and physics.
Managing the workload, along with sport, volunteering and school leadership positions means she ought to be well placed to cope with the step up to med school, though I understand the pace is still likely to be tough.
I wonder if chemistry as a requirement is more about showing you have the ability to understand concepts, rather than the knowledge learnt at school.