Part 1: Bananas in Pyjamas

Fact: Bananas can kill you.

Bananas are great for your health – they’re packed with essential ions, full of fibre and they come with their own handy natural wrapping. They can now even be a way of getting vaccinations to the poorest areas of the world. But where pineapples and then apples were out to get you, now bananas have joined in the fight to put you to bed for good. That fruit bowl is starting to look awfully sinister.

Bananas are packed with potassium, an essential ion that’s in all our cells. Potassium (along with sodium) plays a vital role in conducting electrical signals through nerves and muscles, so it’s essential to keep us alive.

Having too little potassium or sodium can play havoc with your nervous system, which is why you get muscle cramps when playing sport in hot weather: you’ve lost so much sodium in your sweat that you can’t relax your muscles.

Nowhere is this balance between sodium and potassium more crucial than in your most important muscle – your heart. The rhythm of your heartbeat is driven by very precise concentrations of potassium and sodium flowing in and out of specialised cells in your heart. Simply put, when sodium flows in your heart contracts, and when potassium flows out your heart relaxes. If the concentration of potassium in your blood rises too high, it blocks sodium from flowing into these cells and triggering a heartbeat.

This means that if you chow down on a massive number of bananas you might raise your blood potassium so much that you stop your own heart. It’s a legitimate risk for people with dodgy kidneys, as your kidneys play a crucial role in keeping your potassium and sodium levels in a healthy balance. For the most part though, don’t worry: a healthy adult would have to eat around 400 bananas in a single day. If you’re eating that many bananas you probably have bigger issues to deal with.

‘Another one of Mr Shaunak’s Little Bites of Science’
Image under Creative Commons license

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