1 Watch the BMI baby : It is easy to get hung up on numbers if you are concerned about your health and your weight.

There’s calories to consider as well as dress and waist size and – of course – your Body Mass Index (BMI) .

This is the ratio of your weight to height and it is universally accepted that once it stays under 25 everything is hunky dory but when it creeps up to 25-29 you are overweight and if it tops 30 you are obese.

Simple, right? Wrong. Most doctors accept, however, that the BMI breakdown is too simplistic and sometimes plain wrong. Brian O’Driscoll is one of Ireland’s most successful professional athletes and, as a result, is quite fit but his BMI suggests he is obese. At 5’ 10” he is short – relatively speaking – and weighs around 15 stone so has a BMI of 30.

Even if you accept BMI as a good guide, weight is not always a good measure of health.

A leading medical institute in Dallas tracked more than 25,000 men over a quarter of a century and assiduously logged who got sick, who died and who didn’t.

Overweight or obese men who took regular exercise died at half the rate of those with a normal weight who rarely or never exercised.

2 Gene janey: While some people do have a genetic predisposition to certain illnesses, environmental factors are far more important than genes. A researcher in Sweden looked at the frequency of various cancers in 45,000 sets of twins and concluded that "genetic factors make a minor contribution to susceptibility" while diet, physical activity and cigarettes and alcohol are much more significant.

3 Hurt heart: To make heart attacks more exciting, film makers frequently show victims grabbing their chests or arms frantically as their faces crease with agony. Yes, heart attacks can certainly hurt, but not always. In fact, you might consider yourself lucky (relatively speaking) if you get chest pains as the most dangerous – and lethal – heart attacks are the ones that either don't hurt or hurt where you don't expect it. Tooth pain is as common as chest pain while a catastrophic sense of doom is a more common telltale sign. The truth is many heart attacks have no symptoms apart from the obvious one – death.

Incidentally, a frequently reproduced “fact” which has spread via email and social media in recent years suggest that you can cough your way out of a heart attack.

While “Cough CPR”could potentially save a person’s life in some circumstances, it should only be tried with the aid of a doctor when a person is losing consciousness and entering cardiac arrest. Doing it wrong can, you know, kill you.

4 Sugar bounce: "Oh don't give him sugar before bed, he'll be bouncing off the walls all night," is a sentiment frequently expressed by parents who are absolutely convinced that sweets bring on instant hyperactivity. They are absolutely wrong. There is no medial evidence linking sugar with hyperactivity. An analysis of the results of multiple studies of the effects of sugar on children's behaviour was published in the Journal of the American Medical Association in 1995 and concluded that sugar in the diet made no difference. The consensus among boffins is that the notion is in parents' minds. They think sugar will cause hyperactivity so that is how they perceive subsequent events. That is not to say you should feed kids sugar with impunity. It is bad for their teeth and their weight.

5 Dim reading: Reading a book in a dimly lit room will not make you go blind any more than the other – slightly more risqué – activity that you may have heard about. The human eye is made of much sterner stuff than that and reading in half light will not damage them. It will make them work harder however and can make concentration difficult as you will have to frequently move the book and your position to see the words so is best avoided .

6 Don't swallow: If you swallow your chewing gum, it will not take years to make its way through your system. Yes, it is indigestible and your stomach acids will not be able to break it down but it will make it through your body in one piece within a matter of days from the swallowing.

7 Hot head: You know how you should always wear a hat in cold weather because you lose 80-90 per cent of your body heat through your head? Well, you don't. You actually lose about 10 per cent of your body heat through your head. Which is the same amount which you lose through your leg or arm.

8 Catch your death: Cold weather does not give you a cold and the absence of a jacket on a cold day will not lead you to "catch your death". The common cold is caused by the rhinovirus and, like all poxy viruses, it doesn't really care what temperature it is outside, it just wants to connect with you. There are several reasons why colds are more common in the winter and one of the leading ones is that we tend to spend more time inside in cold weather so the chances of viruses passing from person to person increase. That's why you are more likely to get sick after a long plane journey too. And speaking of viruses, it is worth remembering that most viruses can't be treated so you just have to wait until they have done their worst and have moved on to the next victim.

9 Vitamin boost: And staying with colds, another medical myth some companies like to sell us is the notion that taking large quantities of vitamin C when you are poorly will make a difference. It really won't. A US study in 2007 focused on 56 trials of vitamin C versus placebo, given as either prophylaxis against, or treatment of, the common cold and found that there was no significant impact on duration of a cold and no clinically significant effect on cold severity.While vitamin C can boost your immune system, by the time you have got a cold it is too late for the curing. And there's no point in taking extra when you're sick as your body can't store excess amounts of the vitamin so once you've hit your 100 per cent, that's your lot.

10 Eat late to gain weight: You would imagine this makes some sense because if you eat a full meal and then go straight to bed you won't have time to burn off any of the calories contained with the meal as you burn off a much smaller number of calories while you are sleeping. Multiple studies have proven that it makes absolutely no difference when you eat. According to the US Department of Agriculture's Weight Control Information Network website, "it does not matter what time of day you eat. It is what and how much you eat and how much physical activity you do during the whole day that determines whether you gain, lose, or maintain your weight."

What you eat and how much you eat are all that matters when it comes to weight gain. Although eating late at night can make for a more unsettled night’s sleep as your body’s digestive rumblings may disturb your sleeping rhythms.