Q: Is soda really bad for your kidneys?

A: Yes. Drinking 16 ounces or more daily (whether diet or regular) doubles your risk of chronic kidney disease, according to an NIH study of more than 900 people. The researchers already knew that consuming any type of soft drink—the average American adult guzzles 59 gallons' worth per year—is associated with several risk factors for kidney disease (hypertension, diabetes, and kidney stones), but the spike in the cola category was remarkable.

Q: Can cracking your knuckles cause arthritis?

A: Nope. If you're suffering from osteoarthritis in your hands, it certainly has nothing to do with this nervous tic. One study at the former Mount Carmel Mercy Hospital in Detroit compared 74 people (age 45 and older) who had been chronic knuckle crackers for decades with 226 who always left their hands alone; researchers found no difference in the incidence of osteoarthritis between the two groups.

Q: It’s safe to follow the 5-second rule for dropped food, right?

A: It's probably not even safe to follow a 1-second rule: The transfer of bacteria from a contaminated surface to food is almost instantaneous—or, at the very least, quicker than your reflexes. In one study, Clemson University food scientist Paul Dawson, PhD, and students contaminated several surfaces (ceramic tile, wood flooring, and carpet) with Salmonella. They then dropped pieces of bologna and slices of bread on the surfaces for as little as 5 seconds and as long as 60 seconds.