Medical myths that come with a health warning

So you know how to keep warm? Think again. Jeremy Laurance reveals research that sets the record straight

Sugar makes kids hyperactive

Many parents have seen the gleam in their child's eye after a can of cola. But Drs Vreeman and Carroll, paediatricians at the Riley Hospital for Children in Indianapolis, say sugar is not to blame for out-of-control offspring. At least 12 double-blind, randomised trials have examined how children react to diets with different levels of sugar – none detected any difference between children who had sugar and those who did not. Even in studies of children with attention-deficit hyperactivity disorder, no difference in behaviour was detectable. Yet when parents believe their children have had sugar they rate their behaviour as more hyperactive, even if what they ate and drank was sugar-free. "The differences were all in the parents' minds," the authors say.

You lose most of your heat through your head

It is widely believed that wearing a hat is the most effective way of staying warm in winter because "40-45 per cent of body heat is lost through the head" (as stated in a US Army manual). But this is wrong. There is nothing special about the head. If it were true, people would be colder going hatless than trouserless, which is "patently not the case", the authors say. The myth arose from a military study which measured heat loss in people wearing Arctic clothing and, as they were hatless, naturally they lost most of their heat through their heads. In fact, people lose around 10 per cent of their body heat through their head. If it's cold outside it makes sense to wrap up, but a hat won't make a huge difference.

Cures for a hangover

None, the authors say. Many are offered, even by medical experts, but no good evidence shows they work. Propranolol, tropisetron, tolfenamic acid, glucose and supplements such as borage, artichoke, prickly pear and Vegemite have all been suggested but all failed to end the throbbing head and heaving gut. (They do not mention the pint of water and paracetamol before bed). The only preventive, they say, is to drink less.

Poinsettias are toxic

The red-leaved Christmas plant is widely suspected of being poisonous. It is not. Of almost 850,000 reports involving plants to the American Association of Poison Control Centres, none of the 23,000 relating to poinsettias involved significant harm. Even in cases where children ate substantial amounts, none needed medical treatment. Parents can relax that the Christmas table decoration is safe.

Suicides increase over the holidays

Dark, cold nights, family dysfunction, loneliness – all can contribute to feelings of despair. But the evidence suggests that while the holidays can be difficult, they also give people something to live for. Studies show suicides decrease in the days before a holiday and increase in the days after. They are also lower in the winter and higher in the summer.

Night food makes you fat

Some diets suggest not eating late helps weight loss and some research backs it. A Swedish study found obese women ate later than slimmer counterparts – but they were fat by eating more meals and their eating pattern was thus extended over a longer time, not because they were night eaters. The timing makes no difference; how much is eaten does.

The research was carried out by Aaron Carroll and Rachel Vreeman of the Indiana University School of Medicine and published in the Christmas issue of the British Medical Journal