Medical myths demystified

More medical myths hit the dust, thanks to Rachel C Vreeman and Aaron E Carroll.

In the pursuit of scientific truth, even widely held medical beliefs require examination or re-examination. Both physicians and non-physicians sometimes believe things about our bodies that just are not true. As a reminder of the need to apply scientific investigation to conventional wisdom, we previously discussed the evidence disputing seven commonly held medical myths.
 
The British Medical Journal generated a list of common medical or health beliefs related to the holidays and winter season and searched Medline for scientific evidence to support or refute these beliefs. If we couldn’t find any evidence in the medical literature, we searched the internet using Google.

Sugar causes hyperactivity in children

While sugarplums may dance in children’s heads, visions of holiday sweets terrorise parents with anticipation of hyperactive behaviour.
 
Regardless of what parents might believe, however, sugar is not to blame for out of control little ones. At least 12 double blind randomised controlled trials have examined how children react to diets containing different levels of sugar. None of these studies, not even studies looking specifically at children with attention-deficit/hyperactivity disorder, could detect any differences in behaviour between the children who had sugar and those who did not. This includes sugar from sweets, chocolate, and natural sources. Even in studies of those who were considered "sensitive" to sugar, children did not behave differently after eating sugar full or sugar-free diets.

Scientists have even studied how parents react to the sugar myth. When parents think their children have been given a drink containing sugar (even if it is really sugar-free), they rate their children’s behaviour as more hyperactive. The differences in the children’s behaviour were all in the parents’ minds.

Excess heat loss in the hatless

As temperatures drop, hats and caps flourish. Even the US Army Field manual for survival recommends covering your head in cold weather because "40 to 45 percent of body heat" is lost through the head. If this were true, humans would be just as cold if they went without trousers as if they went without a hat. But patently this is just not the case.

This myth probably originated with an old military study in which scientists put subjects in arctic survival suits (but no hats) and measured their heat loss in extremely cold temperatures.
 
Because it was the only part of the subjects’ bodies that was exposed to the cold, they lost the most heat through their heads. Experts say, however, that had this experiment been performed with subjects wearing only swimsuits, they would not have lost more than 10% of their body heat through their heads. A more recent study confirms that there is nothing special about the head and heat loss. Any uncovered part of the body loses heat and will reduce the core body temperature proportionally. So, if it is cold outside, you should protect your body. But whether you want to keep your head covered or not is up to you.

Nocturnal feasting makes you fat

Holiday feasts and festivities present us with many culinary options. A common suggestion to avoid unwanted weight gain is to avoid eating at night, and at first glance, some scientific studies seem to support this. In a study of 83 obese and 94 non-obese women in Sweden, the obese women reported eating more meals, and their meals were shifted to the afternoon, evening, or night. But just because obesity and eating more meals at night are associated, it does not mean that one causes the other. People gain weight because they take in more calories overall than they burn up. The obese women were not just night eaters, they were also eating more meals, and taking in more calories makes you gain weight regardless of when calories are consumed.

Other studies found no link at all between eating at night and weight gain. Swedish men did not show any evidence of gaining weight with night time meals. In a study of 86 obese and 61 normal weight men, there were no differences in the timing of when they ate. Another study of 15 obese people found that the timing of meals did not change the circadian rhythm pattern of energy expenditure.
 
In a study of over 2500 patients, eating at night was not associated with weight gain, but eating more than three times a day was linked to being overweight or obese. Studies have connected skipping breakfast with gaining more weight, but this is not because breakfast skippers eat more at night. Breakfast skippers eat more during the rest of the day. Records of calorie intake suggest that those who eat breakfast maintain healthy weights because their calorie intake is more evenly distributed over the day. In other words, when you eat three regular meals, you are not as likely to overeat at any one particular meal or time.