Archive 2007 2008 2009 2010

Q: You have said that smokers shouldn't take beta carotene pills. I don't smoke, but I drive a bus and am exposed to lots of diesel exhaust in the bus yard. I take 30 milligrams of beta carotene to protect myself. Is this a good idea?
J.P., VIA THE INTERNET

A: No. We do not recommend beta carotene supplements for anyone. Diesel exhaust is a serious occupational hazard, notably for bridge and tunnel workers, truck and bus drivers, machine operators, and mine and railroad workers. Its potential adverse health effects range from headaches and nausea to cancer and respiratory disease.

There is no evidence that beta carotene supplements can protect against the damage caused by diesel exhaust. They may even make the risks worse. Many people take these pills because they are antioxidants and thus may help reduce the risk of cancer—or so it was thought. But a few years ago two important studies found that beta carotene supplements actually increased the risk of lung cancer in smokers and in asbestos-industry workers (see WELLNESS LETTER, March 2000). Beta carotene pills may have the same adverse effect in people exposed to air pollutants. There are no studies on this, but why take the chance?

Instead of taking beta carotene pills, if you belong to a union, talk to your leaders about getting the company to switch to nondiesel buses—or at least supply adequate ventilation.

In the meantime, make sure your diet is healthy—with lots of fruits and vegetables, especially those rich in vitamin C. It's safe to eat foods rich in beta carotene

And by the way: California is attempting to decrease the use of diesel fuel. This issue concerns us all, not just bus and truck drivers. We'll discuss diesel pollution in an upcoming issue.

Q: What do you know about inversion therapy for back pain? The ads claim that hanging upside down can reverse the effects of gravity and increase the space between the vertebrae.
A.P., VIA THE INTERNET

A: Inversion therapy for back pain is an old idea that waxes and wanes in popularity. Now it seems to be waxing: the Internet offers a variety of tables (at $200 and up), chairs, boots, and other devices to facilitate hanging upside down. But there is little evidence that inversion therapy produces any benefit for back pain, except perhaps a temporary one. This is a form of traction—a method that's largely been discarded for treating back pain.

Inversion devices, according to Dr. Gary Brazina, an orthopedic surgeon and sports medicine specialist in Los Angeles, don't actually reverse the effects of gravity or increase the space between vertebrae, though they may temporarily extend the spine and briefly relieve muscle spasm. Potential side effects from hanging upside down include bleeding into the retina and headaches. It can also make some back problems, as well as hypertension, worse.

If you have back pain, consult a professional skilled in back care. Ask about treatments and exercises for your back. Inversion therapy is unlikely to help and may be harmful. Be skeptical of the wild claims made on websites selling inversion devices.

Bottom line: Don't try inversion therapy, especially not if you have heart disease, hypertension, glaucoma or other eye diseases, or are pregnant. If you do decide to try it, at least make sure there's someone around in case you need help.

Q: What ever happened to RDAs for vitamins and minerals? Now I read about DRIs and Daily Values instead.
P.M., VIA THE INTERNET

A: The government's RDAs (recommended dietary allowances) are still used by scientists and nutritionists. But they're now part of a larger set of guidelines called the Dietary Reference Intakes (DRIs), which have been devised for 17 vitamins and minerals, plus beta carotene (which the body converts into vitamin A) and other carotenoids.

Besides the RDAs, the DRIs include AIs (adequate intakes, for nutrients without RDAs), ULs (tolerable upper limits), and EARs (estimated average requirements).

The new guidelines were developed by the U.S. and Canada to help decrease the risk of chronic diseases such as osteoporosis, cancer, and heart disease, not just to prevent deficiencies.

There's still another set of terms, called Daily Values (DVs), used on nutrition labels on foods (and supplements). The labels tell you what "% Daily Value" a serving supplies of various nutrients in a 2,000-calorie daily diet. DVs are based on RDIs (reference daily intakes, based on the 1968 U.S. RDAs) and DRVs (daily reference values, for other nutrients such as fat and protein). Fortunately, these last two abbreviations do not appear on the labels.

Words to the wise: These maddeningly similar-sounding terms and abbreviations have left even many nutrition experts scratching their heads. There's no need to try to keep all this straight. The RDAs are the numbers to go by. We usually list them when we write about individual vitamins or minerals. You should know how to use the DVs on food labels, which we will discuss in an upcoming article.

Q: Why didn't you mention black currants in your article on berries? They are even more nutritious, and are especially rich in vitamin C.
D.M., VIA THE INTERNET

A: Black currants (Ribes nigrum) are indeed very nutritious—a cup contains about 200 milligrams of vitamin C, more than double the daily RDA. But black currants aren't grown or eaten much in this country, in large part because they are too tart to eat fresh; they're more common in Europe, where they're often made into a liqueur called cassis and also into juice or nectar. Fresh currants are sometimes used for jams and jellies, but this destroys most of the vitamin content.

You may be thinking of dried currants, which are more common here. These are not currants, but tiny raisins made from a special kind of small grape. High in calories and expensive, they're a little more nutritious than regular raisins—rich in iron, potassium, fiber, and B vitamins (but with far less C than fresh black currants). However, if you're adding an ounce or two to a recipe, the nutrients don't add up to that much.