Health and medical advice can change frustratingly frequently. Is coffee good for us or bad for us these days? (Good.)

That's why, when it comes to your general health, it's hard to know what information is right, wrong, or somewhere in between.

To find some of the most common health questions that people have, we turned to a book called "Your Health: What Works, What Doesn't" published by Reader's Digest in June 2010.

The book consulted dozens of experts and culled through hundreds of studies to bring readers a definitive answer to controversial questions about diet, fitness, disease, and medicine.

We've supplemented these answers with our own research to present a bottom line.

Keep in mind that new research continuously changes our understanding of "good and bad" health advice. We've done our best to provide answers based on the most current scientific evidence.

Does olive oil prevent heart disease?

Short answer: Yes

The health benefits of olive oil come from the presence of polyphenols, antioxidants that reduce the risk of heart diseases and cancers.

But to get these healthy compounds, consumers should buy good-quality, fresh "extra-virgin" olive oil, which has the highest polyphenol content. Most commercially available olive oils have low levels of polyphenols associated with poor harvesting methods, improper storage, and heavy processing. 

Do cough syrups work?

Short answer: No

In 2006, the nation's chest physicians agreed that the majority of over-the-counter cough medicines don't actually work. These colorful syrups typically contain doses of codeine and dextromethorphan that are too small to be effective.

Only cough suppressants that contain older antihistamines seem to relieve coughs. That includes brompheniramine, an active ingredient in Dimetapp.

Does sugar cause hyperactivity?

Short answer: No

Following a review of 23 studies, a 1996 report published in the Journal of the American Medical Association concluded that sugar "does not affect the behavior or cognitive performance of children."

The age-old myth that kids misbehave when they eat large amounts of candy, cookies, and other junk food, could be related to the type of events where these foods are typically served. For example, kids are more wound-up at birthday parties and during Halloween when sweet treats tend to flow freely.

Do sugary soft drinks lead to diabetes?

Short answer: Yes

The majority of health research is stacked against sugar-sweetened soda. A large 2004 study in the Journal of the American Medical Association found that women who drank one or more sugary drinks per day increased their risk of developing type 2 diabetes by 83% compared to those who consumed less than one of these beverages per month.

Do I need sunscreen with more than 30 SPF?

Short answer: No

Sunscreens with an SPF (sun protection factor) of 30 block about 97% of ultraviolet rays, while sunscreens with an SPF of higher than 30 block 97%-98%.

It's more important that you choose "broad-spectrum" sunscreen, meaning it protects against both UVB and UVA rays. Sunbathers also need to apply a generous amount of sunscreen in order to get the full benefit of the SPF.

Is the MSG in Chinese food likely to give you a headache?

Short answer: No

A review of 40 years of clinical trials, published in the journal of the American Academy of Nurse Practitioners in 2006, found that all previous research "failed to identify a consistent relationship between the consumption of MSG and the constellation of symptoms that comprise the syndrome," including headaches and asthma attacks.

The misconception spawned from several poorly done, small studies in the 1960s that seemed to connect MSG with a variety of maladies that people experienced after eating at Chinese restaurants — though a number of Chinese restaurants now avoid MSG because of that misconception.

Learn more about the MSG myth here »

Do nuts make you fat?

Short answer: No

As much as 75% of a nut is fat. But eating fat doesn't necessarily make you fat. The bigger factor leading to weight gain is portion-size. Luckily, nuts are loaded with healthy fats that keep you full. They're also a good source of protein and fiber.

One study even found that whole almonds have 20% less calories than previously thought because a lot of the fat is excreted from the body.

Is walking as effective for weight loss as running?

Short answer: Yes 

Studies have shown that how long you exercise is more important than how hard you exercise — at least in terms of calories burned. Running is a more efficient form of exercise, but you can burn just as many calories by walking.

A six-year study published in the journal Arteriosclerosis, Thrombosis, and Vascular Biology in April found that walking at a moderate pace and running produced similar health benefits, so long as the same amount of energy was expended.

However, there is some evidence that vigorous exercise might be significantly better for your heart than moderate exercise, even while done for short durations of time. So while running might not be better for weight loss, it might be important to include running or other intense workouts into your schedule for general health.

Is drinking fruit juice as good for you as eating fruit?

Short answer: No

Calorie for calorie, whole fruit provides more nutritional benefits than drinking the pure juice of that fruit. That's because when you liquefy fruit, stripping away the peel and dumping the pulp, many ingredients like fiber, calcium, vitamin C, and other antioxidants are lost.

For comparison, a five-ounce glass of orange juice that contains 69 calories has .3 grams of dietary fiber and 16 milligrams of calcium, whereas an orange with the same number of calories packs 3.1 grams of fiber and 60 milligrams of calcium.

Are all wheat breads better for you than white bread?

Short answer: No

Not all wheat breads are created equal. Wheat breads that contain all parts of the grain kernel, including the nutrient-rich germ and fiber-dense bran, must be labeled "whole grain" or "whole wheat."

Some wheat breads are just white bread with a little bit of caramel coloring to make the bread appear healthier, according to Reader's Digest.

Can a hot tub make me sick?

Short answer: Yes

Hot tubs — especially ones in spas, hotels, and gyms — are perfect breeding grounds for germs.

The water is not hot enough to kill bacteria, but is just the right temperature to make microbes grow even faster. Even though hot tubs are treated with chlorine, the heat causes the disinfectant to break down faster than it would in regular pools.

The most common hot tub infection is pseudomonas folliculitis, which causes red, itchy bumps. A more dangerous side-effect of soaking in a dirty Jacuzzi is a form of pneumonia known as Legionnaire's disease. This is what reportedly sickened more than 100 people at the Playboy Mansion back in 2011.

Does coffee cause cancer?

Short answer: No

Coffee got a bad rap in the 1980s when a study linked drinking coffee to pancreatic cancer. The preliminary report was later debunked.

More recently, health studies have swung in favor of the caffeinated beverage. Coffee has been linked to a lower risk of type 2 diabetes, Parkinson's disease, prostate cancer, liver cancer, Alzheimer's disease, and even suicide.

So go ahead and pour yourself a mug of coffee — or two.

Do eggs raise cholesterol levels?

Short answer: No

Although egg yolks are a major source of cholesterol — a waxy substance that resembles fat — researchers have learned that saturated fat has more of an impact on cholesterol in your blood than eating foods that contain cholesterol. 

"Healthy individuals with normal blood cholesterol levels should now feel free to enjoy foods like eggs in their diet every day," the lead researcher from a 25-year University of Arizona study on cholesterol concluded. 

Can you drink too much water?

Short answer: Yes

It is very rare for someone to die from drinking too much water, but it can happen.

Overhydrating is most common among elite athletes. Drinking an excess of water, called water intoxication, dilutes the concentration of sodium in the blood leading to a condition known as hyponatremia. The symptoms of hyponatremia can range from nausea and confusion to seizures and even death in severe cases.

To avoid this, drink fluids with electrolytes during extreme exercise events.

Can yogurt ease digestive problems?

Short answer: Yes

Our digestive tract is filled with microorganisms — some good and some bad. Most yogurt contains beneficial bacteria, generically called probiotics, that helps maintain a healthy balance. Probiotics can relieve several gastrointestinal problems, including constipation and diarrhea.

However, not all yogurt contains the particular species of bacteria that might help an individual. And even though certain brands of yogurts are marketed exclusively to treat tummy issues, regulators have concluded that some companies that make those claims have overstated the benefits of their product.

Do whitening toothpastes whiten teeth more than regular toothpastes?

Short answer: No

Whitening toothpastes usually contain peroxides and other strong abrasives that might make your teeth appear whiter by removing stains. Unlike at-home whitening strips and gels that contain bleach, these toothpastes do not actually change the color of your teeth, they simply remove surface stains from things like coffee and wine.

Is it safe to microwave food in plastic containers?

Short answer: Yes

But the plastic container should display the words "microwave safe." This means that the Food and Drug Administration has tested the container to make sure no chemicals used to make the plastic leech into foods during microwaving. If chemicals do seep out into food, the amounts are tiny and not dangerous to our health.

As a general guideline, plastic grocery bags as well as most plastic tubs that hold margarine, yogurt, cream cheese, and condiments are not microwave safe.

Still, evidence on safe and unsafe plastics does change. Certain plastic makers removed the chemical BPA due to concerns about whether or not its safe. However, recent studies have shown that other chemicals that replaced BPA in those plastics may be just as potentially harmful. So if anything about plastics makes you uncomfortable, go ahead and use a glass bowl or jar to microwave products.

Can watching TV ruin your eyesight?

Short answer: No

Watching TV will not destroy your rods and cones as the outdated myth suggests. Before the 1950s, TVs emitted radiation that could increase an individual's risk of eye problems after excessive TV viewing. Modern TVs have special shielding that blocks these harmful emissions.

In fact, some activities that involve a TV, like playing video games, may actually improve your eyesight.

Is red wine better for you than white wine?

Short answer: No

Red wine's benefits have been touted because red wines contain much more resveratrol than white wine. Resveratrol is an antioxidant found in the skin of grapes that some studies showed might help fight off diseases associated with aging.

However, more recent studies have shown that the levels of resveratrol found naturally in food aren't high enough to make a difference in terms of less inflammation, reduced risk of cardiovascular disease or cancer or increased longevity.

Is bottled water better for you than tap water?

Short answer: No

Bottled water is no safer or purer than tap water, although it is substantially more expensive.

A recent study by Glasgow University in the U.K. found that bottled water is actually more likely to be contaminated than water from your faucet because it is less well-regulated.

Bottled water and tap water typically come from the same sources — natural springs, lakes, and aquifers. While public water supplies are tested for contaminants every day, makers of bottled water are only required to test for specific contaminants every week, month, or year.

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