Parents may think that sugar makes children hyperactive, but it's a myth, say researchers who analyzed evidence on this and other festive medical folklore.

For the Christmas issue of the British Medical Journal, Dr. Aaron Carroll and Dr. Rachel Vreeman of the Indiana University School of Medicine debunk common holiday myths that have little evidence in scientific studies.

The pair said they did the study to remind people of the importance of keeping a healthy skepticism.

"Only by investigation, discussion, and debate can we reveal the existence of such myths and move the field of medicine forward," they wrote.

For example, the idea that sugar from sweets, chocolates and pop makes children hyperactive is most likely in parents' minds, the researchers said, based on their review of at least 12 studies.

Parents were so convinced about the myth that when they think their children have been given a drink containing sugar (when it is actually sugar-free) they rated their children's behaviour as more hyperactive.

"Regardless of what parents might believe, however, sugar is not to blame for out-of-control little ones," the researchers wrote.

Head heat loss

Another myth they debunked was that people lost up to 45 per cent of their body heat through the head.

The myth likely originated in a military study where scientists put subjects in Arctic survival suits without hats and measured heat loss in cold temperatures. Participants did lose most heat through their heads, but only because it was the only bare part of the body.

A more recent study that repeated the experiment with subjects wearing only swimsuits suggested the subjects would have have lost no more than 10 per cent of their body heat through their heads.

Carroll and Vreeman recommended keeping all parts of the body warm when out in the cold, but the head does not need special attention.

Other myths included:

• Eating at night makes you fat. False. People gain weight because they take in more calories overall than they burn up, regardless of when the calories are consumed.
• Drinking water, taking Aspirin, eating bananas, etc. will cure a hangover. False. "A hangover is caused by excess alcohol consumption. Thus, the most effective way to avoid a hangover is to consume alcohol only in moderation or not at all," the pair said.
• Suicides increase over the holidays. False. Studies conducted worldwide offer no evidence of a Yuletide peak. Suicides are actually more common during warm and sunny times of the year, they said.

The study is a followup to one the researchers published last year on other medical myths, such as that people should drink eight glasses of water a day and that reading in dim light ruins eyesight.

The pair will publish a book next year on other myths and half-truths about body and health.