SIX COMMON MEDICAL MYTHS

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Could the sage advice passed down for generations be downright untrue? See what words of wisdom we've exposed.

Some medical advice gets passed down from generation to generation with such authority we never doubt their truth. They remain unchallenged mostly because they are completely plausible, despite the fact that there is no solid evidence to back them up. Plus, who would question the common wisdom of our mothers, teachers and doctors who advise us with such conviction.

Here are some unfounded, yet wildly common medical recommendations that even slip past the medical professionals.

1. Sugar makes kids hyperactive

Nothing would make a parent happier than finding the cause of hyperactive behavior. But alas, the sugar-hyperactivity myth has been debunked. There have been numerous studies looking at the role of dietary sugar in children and there is no evidence that it makes kids hyper. They tested the effects of natural sugars such as those found in fruit and added sugars like those found in candy bars. Interestingly enough, parents perceived their child as hyperactive when they were told they had consumed a sweetened soft drink, when in fact, it was sugar-free.

2. You should drink 8 glasses of water a day

This little ditty has been circulating since a 1945 guideline recommendation from the Nutrition Board of the National Research Council (NRC) read, "An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods."

For some reason the last sentence, which is really an important point, got cut from the story telling. Hence the 8, 8-ounce glasses of water a day rule persisted. What the board really meant was humans need 2.5 liters of fluid a day (assuming a 2500 calorie diet). But fluid comes from many sources, not just water alone, including other beverages such as coffee and from fruits, vegetables, yogurt and rice.

Healthy people at rest naturally maintain a water balance and what you don't use you excrete as urine. Still, if you consume too much water too quickly, you can get water toxicity, a potentially life-threatening situation where the kidneys just can't manage processing large quantities of fluid all at once.

3. You lose most of your body heat through your head

If you check the US Army Survival Manual's basic principal of cold weather survival it says to always keep your head covered because you can lose 40-45% of your body heat from an unprotected head. Tell that to the guy standing outside with no pants on. Truth is you lose no more heat from your head than any other portion of your body. Any part of your body exposed to the cold will drop core body temperature. When emergency medical technicians treat for hypothermia, they apply heat to the chest, neck, armpits and groin. The head? Not so much.

4. Going out in the cold or the rain will make you sick

You can hear mothers everywhere calling their kids back inside from playing outdoors in the cold, shouting that they will catch their death. Being wet and cold can certainly make you feel lousy, but it doesn't make you sick. Even when scientists put cold viruses directly into people's noses, people who were chilled were no more likely to become ill than those who were warm and comfortable. We may get sicker during the winter months, but that's not because we are out in the cold.

Cold and flu viruses are transmitted from person to person through close contact and we all tend to congregate more indoors when it's cold or rainy outside. Close up the house and crank up the heat (or air-conditioning) and you dry out the natural protective mucous in the nasal passages making it more conducive for viruses to sneak into the bloodstream.

Actually being a little cold might provide some benefits. One study found that cooler temperatures actually stimulated parts of the immune system.

5. Beer before liquor, never sicker, liquor before beer, you're in the clear

If you are looking for a way to hedge a hangover, this sequence of imbibing is not going to do a thing. Alcohol is alcohol and it all gets metabolized and absorbed in the same way. If you have a hankering for hard liquor, pick the clear ones. Darker liquors contain congeners, the impurities produced during the fermentation process that contribute to hangovers. Still, there are no known cures for a hangover so it's best to consume less or not at all.

6. You shouldn't dye your hair during pregnancy

There is no solid evidence that the fetus is harmed when a mother dyes her hair during pregnancy. An insignificant amount of the chemical agents used in processing is absorbed.

You can read about these myths and many more in Don't Swallow Your Gum!: Myths, Half-Truths and Outright Lies About Your Body and Health by Dr. Aaron Carroll and Dr. Rachel Vreeman (St Martin's Griffin.)