Here are some common medical myths that are easy to dispel:

We Only use 10% of our brain

This is a fairly innocuous start to the list. As with any truth claim, it’s good to come at this one through both plausibility and scientific angles.

It’s implausible that we would have evolved a brain that we don’t use - it would be a massive waste of evolutionary development to create, and a waste of energy to keep. Evolution is frugal, and traits that aren’t needed aren’t selected for, and tend not to become a part of our genome, so it’s unlikely that we’d evolve a brain that we don’t use properly. Also, if we imagine a brain where we once used 100% but don’t any more, we have another problem. Genetic features we have that aren’t used - such as the eyes of fish who live in caves - fall prey to genetic changes over time that render them useless. If a particular gene is not useful, there’s no selective pressure to ensure it doesn’t not suffer random deleterious mutations over generations and become unusable.

Of course, these days we can test this idea by measuring brain activity. What we see is that different areas of the brain are responsible for different functions - such as balance, language processing and reasoning. While we may not always be using all of these parts of the brain to their full potential, all parts of the brain have specific tasks and are all used regularly. There is no 90% of the brain that’s sitting there dormantly, waiting for meditation or hypnosis to unlock it.

More X happens on a full moon

There are ideas out there that people act differently when there is a full moon - more people with mental health issues have flare-ups, more accidents occur due to reckless behaviour and more babies are born. I have three children, and have asked each of the three midwives their thoughts on this. All told me that it’s true - more babies are born around the time of a full moon than any other time of the month, making the full moon their busy time.

However, this is an easy one to check because of medical admissions records. And thankfully the work’s already been done. The result? No spike in any of these statistics around full moons. This is simply one of those ideas that feels plausible, and for those who work in the relevant medical fields once they think it’s true, confirmation bias will tend to reinforce their belief - so when they’re busy and they notice it’s a full moon, it reinforces their belief, but when they’re busy at other times of the month it’s not important and tends to be forgotten. So people can end up spending their life believing something that’s not true, and seeing more "evidence" over time to back it up, ending up with a strong, but erroneous, belief.

Kids get a sugar rush

This idea was popularised by Dr. Ben Feingold in his book "Why Your Child Is Hyperactive", from back in 1975. It turns out that, in blinded tests where sugary treats and a sugar free alternative are used, kids are no more active or unruly with the sugary treats than with the sugar free ones - if anything, measurements of their activity has shown them to be more lethargic. However, when parents are brought into the mix, they tend to see their kids’ behaviour as worse if they are told the kids have been fed sugary treats - whether the kids had the sugar or the substitute.

Amber beads help babies with teething

The idea here is that succinic acid released by amber can help with teething pain, and therefore an amber bead necklace. Not only does succinic acid not actually help with teething pain, but amber bead necklaces also don’t excrete a meaningful amount of the acid - plus it’s not readily absorbed through the skin. When you combine this lack of use with the very real danger of a baby being choked either by strangulation or by swallowing beads from a broken necklace, it’s surprising that any parent is still using these.

https://bmccomplementmedtherapies.biomedcentral.com/articles/10.1186/s12906-019-2574-9

Chewing gum stays in your stomach

Don’t believe what you were told as a kid about gum - it doesn’t stay in your stomach if you swallow it. Like pretty much everything else your body ingests and does not need, it gets excreted out of the other end pretty quickly. There’s no ball of chewing gum stuck in your stomach or intestine - your digestive system is a well-oiled machine that takes what it needs and pushes out everything else. The same goes for unspecified "toxins" that you may be told have accumulated inside you from years of eating junk food. This is not the case, and you don’t need a detox diet or colonic irrigation to help clear your body out.

There are exceptions here, as some chemicals such as heavy metals (e.g. mercury, arsenic or lead) can bio-accumulate in the body. However, this is a rare issue and your body will normally let you know by being sick - at which time your GP will diagnose heavy metal poisoning and send you for a treatment called chelation that involves swallowing a chemical that will bond to the heavy metal and allow your body to flush it out.

We need to take vitamin tablets to stay healthy

Despite what health gurus and vitamin companies might want you to think, most people don’t need vitamin supplementation. A normal western balanced diet, even if it contains some junk food every day of the week, gives us all the vitamins and minerals we need. The people who should be taking vitamin supplements are those who have been prescribed one by their doctor. In fact, in some cases taking vitamin supplements when they haven’t been prescribed can be dangerous. If you’re unsure, talk to your GP and they’ll advise you.

Vitamin C helps with colds and flu

Sticking to the topic of vitamins, it’s one of those "well known" facts that vitamin C helps protect against, and treat, colds and flu. The evidence is more nuanced on this one, with a recent review of studies suggesting that there is some benefit, but not a lot. Vitamin C is certainly not going to stop you getting sick, but it may help shorten the length of your illness. And the advice given by experts is to keep your vitamin C at acceptable levels by eating a balanced diet - not with vitamin C tablets, and definitely not with megadosing of vitamin C - which can cause nausea and diarrhea. Running out to the chemist when you’re already sick to buy vitamin C tablets is too little, too late.

Feed a cold, starve a fever

While we’re on the topic, "feed a cold, starve a fever" is not useful advice either. From what I can tell this comes from the idea that food makes you warm, and that a "cold" means you need food to bring your temperature up while the high temperature of a fever requires you to bring your temperature down. It’s overly simplistic to think that you can help treat a complex medical condition by making a superficial change to one of its symptoms. The best advice is to eat when you can. When your body is fighting disease, it needs energy - which it gets from food. Eat when you can, and bear in mind that your body has some good ways of telling you when it’s not ready for food - nausea and vomiting being two of them.

Being cold makes you more likely to catch a cold/flu

This is a classic old wives’ tale - the idea that cold weather or temperature will make you more susceptible to catching a cold or other disease. The common cold was tested for this phenomenon as far back as 1968, and it was shown that people who were cold enough to be shivering were no more likely to catch a cold than those who were warm. Of course there may well be other factors at play here, such as people being more likely to be huddled up together in a warm enclosed space in cold weather, which could increase exposure to, and transmission of, viruses. There’s also evidence that viruses live longer outside the body in cold, dry air. However being cold in and of itself won’t make you more likely to be infected with the cold virus.

6-8 glasses of water a day

This idea is particularly popular in the US, and appears to come from the US Food and Nutrition Board, who in 1945 told the public that the human body needs over 2 litres of water a day. What’s been lost in translation is that we all get most of this from our food, given that most food has a high water content. You don’t need to drink 8 glasses of water a day!

The other thing to bear in mind is that our body has a simple mechanism of telling us when we need water - thirst. Although there are medical conditions that disrupt this, in most people a good general rule is to drink water when you’re thirsty.

Vaccines cause autism

This is at the dangerous end of medical myths, and is oddly persistent. It seems to be part of every modern day conspiracy theorist’s grab-bag of ideas, and is one of the many ways that those distrustful of government, and authority in general, think that we’re being lied to, and poisoned, by those in power.

There is a mountain of evidence that shows no causal link between the MMR vaccine, or any vaccine, and autism. Vaccines can occasionally have unwanted side effects, and can be dangerous for some people with certain bad allergies. But, overall, these medical marvels are doing much, much more good than bad. Efforts to convince people to opt out of giving vaccines to their children are dangerous, and doing us all a disfavour.

Also, despite anecdotal evidence that I’m sure most people have heard from colleagues, friends and family, the flu vaccine does not give you the flu.