Archive 2005 2006 2007 2008

Q: Will a humidifier help prevent colds in the winter?

A: It’s hard to say. Dry air can irritate nasal passageways and the throat, possibly making them more susceptible to infection. And if you already have a cold, dry air dries mucus, which makes it hard to clear from your body. That’s why steam or moist air is useful when you’re congested and sick—to help loosen mucus. Colds are caused by viruses, however, and humidity does not get rid of them or shorten the duration of infections.

Humidifiers do help some people breathe better when the air is cold and dry. But when improperly cleaned and maintained, humidifiers can actually be a breeding ground for many microorganisms, which can lead to infections, asthma symptoms, and allergies. Follow the manufacturer’s instructions, which usually require emptying the water from the tank daily. Every one or two weeks, disinfect the tank using a mixture of one teaspoon of chlorine bleach to one gallon of water. Allow this to sit for 20 minutes before thoroughly rinsing with a 50% solution of vinegar—this should eliminate mold.

Too much humidity can be a problem, too. People who live in damp houses have higher rates of respiratory problems, including infections and asthma. High humidity can, for instance, increase mold in a house, which can cause cold-like symptoms. Water damage, poorly ventilated bathrooms and kitchens, and appliances such as humidifiers, air conditioners, and even dehumidifiers (if not emptied) can add excessive moisture. The relative humidity level in your home should be 30 to 50%; you can measure it with a simple device called a hygrometer, available at hardware stores.

Q: Does the Virulite, a laser device, work for cold sores?

A: Perhaps. Virulite, a small battery-powered machine, emits a particular wavelength of light via a low-level laser beam. It does not directly affect the virus that causes cold sores (herpes simplex), but may stimulate healing and is claimed to prevent recurrences. It’s approved as a medical device in Europe and Canada, but not in the U.S. No harmful side effects have been reported, and it’s easy to use. It costs about $100.

Studies of Virulite have appeared in scientific journals; some have been promising, but the evidence is inconclusive. One small study found that Virulite cut healing time from eight to four days. However, there has been no carefully controlled trial comparing Virulite to oral antiviral drugs (acyclovir and related drugs), which are safe and effective treatments for cold sores.

Until more research has been done on Virulite, stick with the drugs.

Q: The label on my yogurt says that one cup supplies 40% of the Daily Value for calcium. What does that mean?

A: It indicates that one cup has 400 milligrams of calcium, or 40% of the Daily Value for calcium, which is 1,000 milligrams.

The Daily Values for vitamins and minerals are based primarily on the RDAs (recommended dietary allowances) set by the National Academy of Sciences as far back as 1968. Current food labels must list the "% Daily Value" for calcium, iron, vitamin A, and vitamin C in a standard serving (other nutrients are optional).

While most RDAs vary by age and sex, the Daily Value is a single number, simplified for use on labels. The RDA for calcium for adults age 19 to 50 is 1,000 milligrams—the same as the Daily Value. But the RDA is 1,200 milligrams for those 51 and older, and 1,300 for children 9 to 18. Thus, if you are over 50, the yogurt provides only about one-third of your daily calcium needs, not 40% as the label says. Still, the "% Daily Value" gives you a ball-park idea of what you’re getting.

Keep in mind: Not all Daily Values reflect current government recommendations. For example, the Daily Value for vitamin C is 60 milligrams, but the RDA was raised to 75 for women and 90 for men. And the Daily Value for vitamin A remains at 5,000 IU, while the RDA is now the equivalent of 2,310 IU for women and 3,000 IU for men.

Q: What does it mean to "lock" your knees, and why do exercise trainers advise against it?

A: Locking your knees means holding them in full extension to the end of their range. When exercising on machines at the gym, for example, or doing calisthenics or weight lifting, locking your knees puts maximum stress on the joint, increasing your risk for injury. Similarly, fully flexing your knees, as in squatting, also increases stress and can cause pain or injury. Even sitting for long periods (as in a car or plane) with your knees at 90° can stress the knee joint. Knees need to move.

Try to avoid the locked knee position when you’re lifting weights, cycling (for instance, if your seat is too high), or doing yoga—or any activity that puts extra weight on your knees. When working out at the gym or in an exercise class, ask a trainer to evaluate your technique.

Q: Your article about the safety of statin drugs didn’t mention pregnant women. Shouldn’t they avoid statins?

A: Yes, the FDA says statins are "category X," meaning they should not be taken by pregnant women since their safety "has not been established." That is true of many drugs. It is unlikely that a doctor would prescribe such a drug to a woman who is pregnant or trying to become pregnant. But women who are (or may become) pregnant should talk to their doctors about the hazards of any medications they take. Though young women are at relatively low risk for heart disease, some are candidates for statins because of their high cholesterol levels and other risk factors.

Animal studies indicate that statins may cause birth defects, but there is limited evidence about this in humans. These drugs block the formation of cholesterol, which the fetus needs in order to develop properly.

The package inserts state that these drugs should be given to "women of childbearing age only when such patients are highly unlikely to conceive and have been informed of the potential hazards." Nursing mothers should also avoid the drugs.

UC Berkeley Wellness Letter, January 2008