12 Medical "Facts" That You Actually Need To Stop Believing

No, shaving doesn't make hair grow back faster.

1. Too much sugar makes children hyperactive.

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According to a big review of all the scientific literature on the topic, it's a total myth. In experiments, kids were given either sugary drinks or ones with artificial sweetener, and there was no noticeable change in their behaviour.

2. When women live together, their periods synchronise.

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A couple of studies in the 1970s seemed to show that this happened, but it has been comprehensively debunked since. The original findings appear to have come about thhrough a combination of total fluke and statistical mistakes.

3. Creative people use the right side of their brain more.

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Lots of people believe it, but the research doesn't back it up. The two halves of the brain are not identical – a lot of your language processing probably goes on in your left hemisphere, for instance – but everyone uses both halves of their brain. There's no evidence that "creative" people use the right hemisphere more, or that "logical" people use the left.

4. Stretching before exercise makes you ache less after it.

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Nope, probably not. A Cochrane Review, a comprehensive roundup of the scientific evidence, looked at 12 studies, and found that warm-ups had only the tiniest effect on delayed onset muscle soreness after exercise.

Several other literature reviews found either no evidence or inconclusive evidence for whether warm-ups reduce the chance of injury, as well, although that may be because not enough good research has been done.

5. You should drink eight glasses of water a day.

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A review of the literature said "no scientific studies were found" which supported it.

The study traced this myth back to a 1940s recommendation by the US Food and Nutrition Board that "a suitable allowance of water for adults is 2.5 liters [roughly eight half-pint glasses] daily". But two sentences later it says "Most of this quantity is contained in prepared foods."

It may have been popularised by a pseudoscientific book by Fereydoon Batmanghelidj, Your Body's Many Cries for Water, which made the "eight glasses" claim and said that asthma, diabetes, Alzheimer's and other diseases were caused by not drinking enough water.

6. Reading in bad light makes you shortsighted.

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There's no evidence for this, and eye doctors say that it doesn't happen. The BMJ included it in a list of "medical myths".

7. Sitting too close to the telly makes you shortsighted.

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No evidence for this either, according to the Royal National Institute for the Blind.

8. We only use 10% of our brains.

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All the bits of your brain have a function, which is why you can't damage any bit of it without noticing the effects. We all use pretty much all of our brains over the course of the day, although not all of it is in use at any given moment.

9. Shaving makes your hair grow back faster or thicker.

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This was debunked way back in 1928 and has been confirmed several times since.

10. Your hair and fingernails continue to grow after your death.

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According to forensic biologists, this doesn't happen, although "shrinkage of the skin can make it seem as though they do".

11. You lose most of your body heat through your head.

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Apparently you only lose about 10%, which is roughly how much you'd expect, given the surface area of your head.

12. Mobile phones cause cancer.

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Two major studies looking at hundreds of thousands of people both found no link.