Consumer reports on Health helps dissuade conventional wisdom health advice that’s not always true.

Conventional wisdom is hard to overturn. Remember when everyone knew they had to drink eight glasses of water a day to stay hydrated? According to the editors of Consumer Reports On Health, that bit of erroneous advice seems to have originated some 70 years ago from a misreading of government recommendations for total fluid intake from beverages and food, not just water.

Even recommendations based on sound research can change over the years. Here’s Consumer Reports On Health’s list of topics where new research is overturning the status quo.

• Antivirals work well against the flu. Current flu strains have developed resistance to two of these drugs, amantadine (Symmetrel and generic) and rimantadine (Flumadine and generic). But in a recent survey conducted by the Centers for Disease Control and Prevention, 27 percent of the physicians who prescribed antivirals continued to use those drugs. The best bet: A yearly flu shot, which helps prevent the flu in the first place.

• Most people get enough vitamin D. More people than ever are donning hats and applying sunscreen as precautions against skin cancer. That’s a good thing, but it’s had an unexpected result: Even in the sunniest climes, there’s now evidence of widespread D deficiency. While there’s some in fatty fish and fortified foods such as milk, tofu and orange juice, many people will need to take a supplement.

• Preventive angioplasty saves lives. The popularity of this procedure, which involves threading a tiny balloon into an artery and inflating it to push a blockage aside, has soared in recent years. But it turns out that the devices pose unexpected risks. More important, doctors now consider heart disease to be a pervasive process that affects the entire web of coronary arteries. So focusing on just one or two blockages, as angioplasty typically does, fails to address the underlying problem.

• Got a cough? Get cough syrup. Coughing is a natural response to rid the throat and lungs of excess mucous, so suppressing it may not be the healthiest choice. A recent study found that up to two teaspoons of honey worked better at quieting coughs in children between the ages of 2 and 18 than either no treatment or a honey-flavored cough syrup.

• Yearly dental X-rays are necessary. Bitewing X-rays, which target specific teeth, are necessary every year only for those with a history of diseased or receding gums or a proclivity for cavities. Otherwise, Consumer Reports On Health experts recommend getting them every two to three years.

• Stretching prevents injured or sore muscles. Many exercisers still believe this, despite a growing body of research to the contrary. For example, one recent comprehensive review found that stretching, either before or after exercise, didn’t help prevent soreness after exercise. To prevent injury from the stretching itself, it’s best to do it after your workout, when your muscles are warmed up.