Can you trust an old wives' tale?

Does eating an apple a day really keep the doctor away? Photo / 123RF

You'll find them first mentioned in the Bible. "Refuse profane and old wives' fables, and exercise thyself rather unto godliness," St Paul warns in his first letter to Timothy. But most of us are still suckers for an old wives' tale, presuming that homely wisdom passed down through the ages must contain at least a grain of truth.

This week, that view was bolstered by no less an authority than Yale University, which suggested that it is indeed easier to catch a cold when you get cold.

In fact, this issue has been one of the most fiercely debated questions in medical science.

Conventional wisdom suggests that colds are caused by viruses - specifically rhinoviruses - not by low temperatures. But the link in the popular imagination persists. One simple idea is that colds spread better in cold weather simply because people are more likely to be indoors, and infections spread far more easily inside than outside. In the Yale study, meanwhile, scientists found that the immune system is weaker in a cold nose than a warm one - meaning our frontline defence against the rhinovirus is compromised.

So which other old wives' tales turn out to be true? And which can we safely dismiss? Here's our (lucky) seven selection.

1. An apple a day keeps the doctor away

Of course this statement cannot literally be true, but there is no doubt that eating raw fruit on a regular basis is a very healthy thing to do. The flesh of an apple contains a protein called pectin, which lowers blood pressure and blood sugar levels. Apples, like most fruits, are also packed with vitamins and essential minerals, including vitamin C and boron, which are essential for maintaining healthy bones. There is good evidence that eating fresh raw fruit on a regular basis lowers blood pressure, reduces the risk of heart disease and cancer, and promotes general wellness, including a boosted immune system. This is perhaps unsurprising, as fruits are the only living objects that have evolved specifically to be eaten.

Are apples the best fruit? The original saying probably came about simply because in the United States and Europe apples are the cheapest and most abundant fruit that most people are likely to have access to. We now know that bananas, oranges, cranberries, blackberries and strawberries all have health-giving properties.

Verdict: Not literally true (apples will not make you immortal), but it is certainly the case that a diet packed with fresh fruit is the one to aim for.

2. Pregnant women should avoid eating unpasteurised cheeses, shellfish and other "edgy" foods

The whole subject of what pregnant women should eat, do and drink has become an ethical, moral and political minefield. The idea that when pregnant you should avoid runny, smelly cheese, prawns or other "grown-up" foods probably comes under the category of a "new wives' tale", as it is certainly not something our grandmothers would have worried about. But it turns out that the science behind this advice is as dubious as the claim that masturbating makes you blind.

Raw (ie, unpasteurised) milk certainly contains a number of potentially nasty pathogens that might cause diseases, such as listeriosis, which can - in theory - cause miscarriages. So surely it is wise for pregnant women to avoid such foods, just to be on the safe side? The problem here is defining "the safe side". While there is a theoretical risk that eating unpasteurised Brie could cause such a problem, there is no actual evidence that it will. In France, where pregnant women consume unpasteurised cheese, shellfish and so on with apparent impunity, rates of listeriosis are actually far lower than in the parts of the United States, Australia and New Zealand where unpasteurised milk and cheese is illegal.

Verdict: False. Be very suspicious of any health claim that appears to restrict the dietary choices of pregnant women.

3. There is a link between the moon and mad, bad behaviour

In many countries police rotas are adjusted to take into account the lunar cycle - assuming the age-old link between a full moon and aberrant, "lunatic" behaviour is in some ways true. But there is very limited evidence for this, for the banal reason that during a full moon there is more light at night, so incidences of certain crimes, such as burglary, are less likely to occur. A major study carried out in 1985 by the American scientists James Rotton and Ivan Kelly found no link between the full moon and psychiatric admissions, car accidents, murders, suicides or other violent crimes. But the myth persists. One likely explanation is that spikes in crime that coincide with full Moons are noticed when that full moon coincides with a public holiday, when crime rates go up anyway. We simply do not notice the other full moons that happen on "ordinary" days.

Verdict: False.

4. Drop a penny from the top of a skyscraper and you could kill someone

This is a surprisingly persistent myth. The idea is that small metal objects have little air resistance and a fall of 1,000ft or more (the height of a typical skyscraper) allows them to reach bullet-like velocities. Unsurprisingly, people have conducted experiments, dropping small coins from great heights and measuring their terminal velocities. It turns out that if you drop a penny (or 1 cent) coin from the top of a skyscraper, it will hit the ground at about 40mph. Enough to leave a nasty bruise perhaps, but not enough to kill you.

Verdict: False. But don't use this as an excuse to throw things off skyscrapers.

5. Red sky at night, shepherds' delight

And red sky in morning, sailors' warning. Many old meteorological rules of thumb (unlike those surrounding infections and diet) turn out to be true. Reading the weather was a matter of life and death for the ancients, and while unpredictable, that weather does show some consistent patterns. In Britain, the prevailing winds are from the west and our prevailing weather systems are low-pressure depressions that come in from the Atlantic, associated with series of warm and cold fronts. Red sky at night (ie, towards the direction of the setting sun) implies a thickening of the cloud layer and perhaps that a front is about to come through. By morning, the front will have passed, giving the typical bright and breezy conditions that hold no peril for someone out on the hills all day with their animals. But a red sky in the morning suggests that a front is on its way, and high winds are about to strike, the last thing a sailor wants to hear.

Verdict: True, in north-west Europe at least.

6. Eating carrots allows you to see in the dark

The story that consuming large quantities of carrots could enable improved night vision arose from the rumour mills of the Second World War. The story - actually propaganda - that British pilots were acquiring night vision capabilities thanks to their diet never really went away. In fact, the carrot became the first ever "superfood". The vegetables do contain carotene, a natural compound that is needed to construct the light-receiving apparatus in the retina, but they won't help your superpowers.

Verdict: False.

7. The soul leaves the body on death, which becomes an ounce lighter

This modern myth was popularised in the film 21 Grams (2003). Surprisingly, it has been checked. Unsurprisingly, there is absolutely no evidence that a soul or anything else departs the body when you die. The idea that there is a tangible metaphysical "you" is very hard to shake off, however. Fascinatingly, although we may not possess souls in the way we used to think, there is a modern technological equivalent of the idea. Computer data in the form of electronic patterns in microprocessor circuits does alter very slightly the weight of those circuits, although the amount is minute.

Verdict: False.