Winter and holiday time can make people act on things they think they know, such as that kids get more hyper when they eat sugar and that we lose body heat through our heads.

But experts say some of those old chestnuts are just medical myths.

Rachel Vreeman and Aaron Carroll from the Indiana University School of Medicine looked at six myths in the Christmas issue of BMJ.

They said that at least 12 studies have shown no evidence that sugary drinks, sweets and chocolate make children hyperactive. In one study, parents were told kids were drinking sugar but it was actually sugar free. Parents still said their kids were wilder.

As for the idea that people lose nearly half of their body heat through their heads, the researchers said that there is nothing special about the head.

"If this were true, humans would be just as cold if they went without trousers as if they went without a hat," they wrote. Covering up your head can still help keep you warm, but it's not particularly important. If it's cold outside it makes sense to wrap up, but covering your head does not make a big difference.

They also debunked the idea that people can avoid getting fat by skipping food at night. The first study that suggested late-night meals lead to weight gain were really just showing that people who ate before bed were having more food overall.

Vreeman and Carroll also said that suicides do not increase over the holidays, poinsettias are not toxic and that hangover cures do not work.