New Delhi, Dec. 21: Reading in dim light will not spoil your eyes and shaving early wont make your hair any coarser. And you can well do without eight glasses of water a day.
Two US paediatricians have demolished a series of medical myths that have long influenced the public and even been espoused by some doctors.
In a paper today in the special Christmas issue of the British Medical Journal, the paediatricians said there is no evidence to confirm some of these myths, while the others have already been proved wrong.
For generations, parents have told children that reading in dim light might harm their vision.
But Rachel Vreeman and Aaron Carroll from the Indiana University School of Medicine, Indianapolis, say such reading habits may cause eye strain but there is no evidence that they can permanently damage eyesight.
They also say reading in bad light causes difficulty in focusing, decreases the rate of eye blinks and leads to discomfort from the drying of eyes, but these effects do not persist.
There are temporary effects, but no proof of permanent damage, Vreeman said.
From their survey of medical literature, Vreeman and Carroll have also found strong evidence against the common belief that shaving causes hair to grow darker and coarser. Studies have confirmed that shaving does not affect the thickness or rate of hair growth.
Shaving removes the dead part of hair, not the living section below the skins surface, so it is unlikely to affect the rate or type of hair growth, the paediatricians said.
But shaved hair lacks the finer taper seen at the ends of unshaven hair and creates the appearance of being coarse, they said. And the new hair appears darker only because it hasnt been exposed to the sun, which tends to lighten hair.
The paediatricians have also attacked a 60-year-old myth Ė that an adult typically needs 2.5 litres, or about eight glasses, of water every day.
Vreeman and Carroll have cited studies that suggest that juice, milk, and even caffeinated beverages such as tea and coffee, could contribute to adequate fluid intake.
Many people feel guilty that theyre not drinking eight glasses of water, but its not necessary, Vreeman told The Telegraph over the phone.
The human bodys mechanism for thirst is very sensitive. The body tells a person when it needs water, she said.
The paediatricians have cited a review in the American Journal of Physiology that has exposed the complete lack of evidence to support the eight-glasses-a-day theory.
Vreeman said the idea of looking for evidence for these beliefs came up when she and Carroll realised during practice that some of them arent true.
We thought this paper would be a light-hearted way to remind people, including doctors, that medicine is not just about adding new knowledge but also (about) questioning existing beliefs, Vreeman told The Telegraph.
The British Medical Journal has traditionally published light-hearted research topics involving diverse facets of medicine in its special Christmas issue. We thought it would be a good home for this paper, Vreeman said.
The other myths the two paediatricians have busted include the beliefs that humans use only 10 per cent of their brains, mobile phones are dangerous in hospitals, hair and fingernails continue to grow after death, and eating turkey makes people drowsy.