6 Common Knowledge Items That Are False

Spinach is a good source of iron

Early spinach testing had contaminated precipitates leading to a too high measurement of iron. It does have as much iron as red meat, but it contains oxalic acid, which makes the iron hard for your body to absorb. Interestingly, E.C. Segar, the creator of Popeye, had his hero eat spinach because of its high Vitamin A content, not because of iron.

Vitamin C helps cure a cold

Linus Pauling (two Nobel prizes) took a lot of Vitamin C and claimed it stopped his frequent colds. Dozens of studies have shown that Vitamin C doesn't appreciably affect colds. It does prevent scurvy, however.

You lose most body heat through your head

This comes from a military study in the 1950s that measured soldiers out in the cold with no hat on. So, the only body part exposed was their heads! It's good to wear a hat, but not because the head is especially good at losing heat. It's that exposed body parts lose heat faster than covered body parts.

A person should drink 8 glasses of water a day.

Comes from a 1945 study that recommended about 2.5 liters of water, but then went on to say that most people get enough water from their foods. It also said that water should be taken ad libitun (as much or as often as necessary or desired) since sensations of thirst usually serve as an adequate guide to drinking water except in infants and sick people.

Sugar cause hyperactivity in children

In 1973, allergy doctor Dr. Feingold, with little to no evidence, recommended that artificial colors and flavors be removed from the diets of hyperactive children. People just added sugar to his already unsupported list. More than a dozen randomized controlled trials failed to detect difference in behavior between kids given large doses of sugar and those who were not. Interestingly, when parent think their kids have been given a lot of sugar, they think their kids are hyperactive, even when the actual substance wasn't high in sugar. 

Microbes outnumber cells in your body by 10 to 1

The original numbers for this calculation came from the 1977 paper "Microbial Biology of the Gastrointestinal Tract". The numbers for microbes (100 trillion) and cells in the body (10 trillion) were pretty much conjured out of thin air. The microbes number came from in a 1972 paper and was a back of the envelope estimate with no experiments. The human cells number from a 1971 text book with no supporting evidence for how the number was derived.

So, what are you believing without testing? As a technologist it is always good to check one's assumptions.