Archive 2006 2007 2008 2009

Q: How long are you contagious when you have a cold?

A: As a general rule, adults with a cold will be able to infect others one day before symptoms appear, and up to five days or so after becoming sick. Infants and children are able to transmit these viral infections for seven days or longer. The precise number of days for transmission can vary from person to person, and also depends on the length of
the illness. Those in poor health tend to get infected more easily. Children are also more likely to catch (and transmit) colds.

Cold viruses, abundant in nasal secretions, are mainly transmitted via hands. When you blow your nose, touch your face, or wipe your eyes, the virus transfers to your hands, and then to whatever or whomever you touch. If you contaminate a telephone, the next person who uses it may catch your cold. To avoid spreading or catching a cold, the most important precaution is to wash your hands often and well. Hand sanitizers are a good option when you’re not near a sink.

Coughing and sneezing can also spread germs, of course. If you don’t have a tissue, instead of sneezing or coughing into your hand, do it into your arm or shoulder, thus avoiding contaminating your hand.

If you think you are getting sick, limit your contacts. Don’t hug and kiss. If you’re around someone who is sick, stay at least three feet away. Airborne cold viruses can’t travel much farther than that. Don’t share drinking glasses, utensils, phones, or towels.

Flu viruses may not travel in exactly the same way as cold viruses, but your best bet is to take these same precautions to avoid transmitting or catching the flu.

Q: I got an email claiming that baby carrots are made from "deformed carrots" and soaked in chlorine, and that the white blush on them is the chlorine surfacing. Is this true?

A: This scare email is full of inaccuracies. When first marketed in the 1980s, baby carrots were cut from misshapen (not nutritionally inferior) carrots to salvage them. But today they are cut and tapered from specially bred carrots—and are more accurately called "baby-cut" carrots. Genuine baby carrots, which are harder to find and expensive, are harvested very young and may retain some greens at the top.

Like other ready-to-eat fresh vegetables, baby-cut carrots are rinsed or sprayed with very diluted chlorine to reduce the risk of bacterial contamination, and then thoroughly washed and bagged. This process is approved by the FDA and accepted by the Canadian Food Inspection Agency, with strict rules for what concentration of chlorine can be used and how long the carrots can be exposed. Chlorine is similarly used as a disinfectant in public water supplies and sometimes in poultry processing. It is toxic at high concentrations, but there’s no evidence that trace amounts left on food and in water are harmful to health.

The whitening that may occur has nothing to do with chlorine. According to Dr. Luke Laborde, Associate Professor Food Science at Penn State University, it is caused by drying of the damaged (peeled) tissue as the carrots are exposed to air. In contrast, whole carrots retain their protective peel.

Don’t forward that email.

Q: How good are heel scans for measuring bone density?

A: Though DEXA (a special X-ray) of the spine and hip remains the standard for diagnosing osteoporosis, ultrasound scans of the heel can be a quick and easy screening tool. Older women with multiple risk factors for osteoporosis, however, should skip heel
scans and go right to DEXA testing.

Several large studies have shown that heel ultrasound can help identify women at high risk for hip and other fractures. And, as is true with DEXA, it may predict fractures even better when the results are combined with an evaluation of other known osteoporosis risk factors, such as your age and body mass index, your history of fractures and falls, and whether you smoke. Like the hip and vertebrae, the heel contains a high proportion of trabecular bone, the spongy type that is more susceptible to thinning.

Besides using smaller, portable, and cheaper equipment, ultrasound testing has other advantages over DEXA. It not only assesses bone density, but may also provide some information about the quality of the bone. And though DEXA uses minimal radiation, ultrasound is radiation-free.

If you have an abnormal ultrasound result, you should have a follow-up DEXA test to confirm a diagnosis of osteoporosis, which helps in decisions about treatment.

Q: Is ghee better for you than butter?

A: No. Ghee is the Indian name for clarified butter—the liquid butterfat produced by melting butter and allowing the water to evaporate and the milk solids to separate out. In India, it’s used as a main cooking fat and in Hindu rituals. In Ayurvedic (ancient Indian) medicine, it’s said to improve digestion, fertility, and memory, among other unproven benefits. In the U.S., ghee is often sold as a "gourmet"—and thus pricier—butter.

Because ghee has a higher smoke point than butter, it doesn’t burn when used in sautéing and thus may generate fewer harmful free radicals. And it keeps longer. On the other hand, according to a 1987 Lancet study, ghee contains a substantial amount of oxidized cholesterol, making it potentially more harmful to arteries than butter, which has none. And like butter, ghee is high in saturated fat (8 grams per tablespoon), with slightly more calories (110 per tablespoon, versus 100 in butter).

No studies have compared the health effects of ghee to butter in people. But some researchers think that ghee may be a factor in the high rates of heart disease in India and in Indian immigrants who continue to cook with it. So limit how much you eat. Indian restaurants typically use large amounts. Some ghee is sold as a blend of clarified butter and partially hydrogenated vegetable oils, which contain unhealthful trans fats. "Vegetable ghee" may consist entirely of partially hydrogenated vegetable oil.

Q: I know that raw fish can contain parasites, but what about lox and Nova?

A: It’s highly unlikely that these forms of commercially preserved salmon pose any danger. Lox is heavily salted, but not smoked. Nova (so called because Nova Scotia is a major source of salmon) is cold-smoked and less heavily salted. Salting does kill parasites, but theoretically they could survive cold-smoking. Still, we could find no reports of parasitic infection from commercial lox or Nova. Furthermore, cold-smoked salmon is almost always deep-frozen before or after smoking, which also kills parasites.

UC Berkeley Wellness Letter, February 2009