13. Can diet soda kill me?
If you mean, could it give you cancer, the answer is probably not. Diabetes? Unlikely. Osteoporosis? Maybe. And it seems possible that the drinks are related to weight gain. Recent research suggests that having several diet drinks a day can weaken bones and is linked to weight gain, though the causes are very murky. Respected nutritionist Marion Nestle, PhD, author of What to Eat and Food Politics, has this to say: "I so prefer real sugar. The other sweeteners are all chemical and all artificial, and I'm not aware of much real evidence that they help people cut calories." A study published this year indicates just the opposite: In rodents, at least, there's evidence that the substitutes interfere with the body's ability to register how many calories it's taking in—which could lead to overeating.
14. Flu shots—should I or shouldn't I?
Yes, absolutely. Although the CDC does not say everyone needs a flu shot, it does recommend them for enough people (due to health risks, age-related concerns, and other factors) that about 82 percent of the total U.S. population qualifies. Even if you don't, you'd be best off getting in line. According to flu expert Trish Perl, MD, a professor of medicine at Johns Hopkins University, "it usually prevents you from catching the flu, but even if you do get sick, your symptoms won't be as severe." More important, it prevents you from spreading the flu to others who might be at risk for developing a fatal case. (About 25 percent of people who have the flu don't even realize it.)
15. Is there any surefire way to stave off Alzheimer's disease?
Sadly, no. The closest scientists have come was a vaccine against synapse-destroying beta-amyloid deposits, a hallmark of the disease. But human trials were stopped abruptly a few years ago when some volunteers developed severe brain inflammation. Still, studies suggest that you can take steps to help your brain—from staying intellectually, socially, and physically active (exercise raises levels of a brain chemical called BDNF that encourages the growth of new brain cells) to eating more fruit, veggies, and salmon.
16. I have to stop eating tuna, swordfish, and salmon, right?
Swordfish, yes. But for most other fish, the benefits of wise consumption outweigh the risks, according to a landmark study in the Journal of the American Medical Association. Swordfish contains high levels of mercury; canned albacore (white) tuna has more mercury than canned light tuna, which is why the Environmental Protection Agency recommends that women of childbearing age eat no more than six ounces of albacore per week. Though salmon does not pose a mercury risk, it may have PCBs (industrial compounds). Limit servings of farmed salmon to one a month; enjoy wild-caught four or more times a month. To learn which seafood is lowest in contaminants and isn't overfished, visit OceansAlive.org.