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Q: Should I take aspirin before a long plane trip to prevent a blood clot?

A: Not unless your doctor tells you to. There is little to support the use of aspirin in preventing travel-related deep vein thrombosis (DVT), also called economy-class syndrome, in which a blood clot forms in a deep vein in a lower leg after you sit for a long time, especially in a cramped position. These clots can cause circulatory problems; they can also break off and travel to the lungs—a potentially fatal condition.

For the average healthy traveler, the chance of developing DVT is extremely low, especially on flights shorter than 6 to 8 hours. The risk increases most after 12 hours of flying and with multiple flights taken over a short time. Other risk factors include personal or family history of clots, recent major surgery, having limited mobility, use of oral contraceptives and hormone replacement therapy, pregnancy, obesity, and cardiovascular disease. Smokers and older people may also be more susceptible.

The Aerospace Medical Association advises that people at increased risk of DVT talk to their doctor about taking aspirin before flying, but no major health organization endorses its use. Of the few studies, one found that 400 milligrams of aspirin taken 12 hours before a flight and for the next few days after did not prevent the condition in high-risk passengers.

Experts generally agree, however, that anyone at increased risk should consider wearing graduated compression stockings on flights over six hours to reduce pooling of blood in the legs. If you are at very high risk, your doctor may also advise an anticoagulant injection before your flight.

And then there are simple steps that all long-distance travelers can take, even on long car, bus, and train trips: Avoid constrictive clothing around your legs and waist (other than compression stockings); drink plenty of fluids; do calf stretches, ankle rotations, and knee lifts; request an aisle seat so you can get up and move about more often; avoid sedatives and too much alcohol.

Q: If I do cardiovascular and strength training on the same day, does it matter which one I do first?

A: If you’re like the average exerciser, it doesn’t matter which you do first, as long as you are not too fatigued to continue. Most people prefer doing the cardiovascular (aerobic) workout first, since it warms up the muscles. But see what works best for you.

If you’re a serious exerciser trying to improve your performance (and not simply trying to stay fit), most sports physiologists recommend doing strength and cardio workouts on alternate days, since one can interfere with the other.

Some studies, for instance, have found that a cardio workout done shortly before strength training can cause muscle fatigue and other physiological changes, and thus may reduce strength improvements. Similarly, doing a strength workout first, followed by cardio exercise—a less common sequence—may reduce your aerobic gains.

However, it depends in part on what kind of workouts you are doing. If your cardio workout is running, for example, and you follow it with upper-body strength training, there’ll be little interaction, since the workouts focus on different muscles. Other variables include how many hours elapse between the two workouts, the intensity and length of workouts, and your fitness level.

Q: In April you listed Zocor and Lipitor among the drugs that don’t mix well with grapefruit juice. But the Zocor insert says that taking Zocor "concomitantly with . . . large quantities of grapefruit juice (more than 1 quart daily) should be avoided." So if I take Zocor, can I drink a glass of the juice hours later?

A: It’s safest not to drink it. Grapefruit and its juice can produce potentially dangerous increases in blood levels of these two statins and many other drugs.

The Merck insert for its cholesterol drug Zocor (simvastatin, now sold also as a generic) specifies more than a quart of juice because nearly all the studies have used such large amounts of (or double-strength) grapefruit juice. Most studies also looked at people drinking some of the juice around the time they took the drugs. Pfizer, the maker of Lipitor (atorvastatin), has no official recommendation about grapefruit juice.

The interaction with grapefruit juice happens fast, and there’s evidence it can last 24 hours or longer, though it trails off. Moreover, the effect can vary from person to person—and even from grapefruit to grapefruit.

Since the effect is unpredictable, it’s best to avoid grapefruit if you take one of the drugs we listed in April. Still, the main concern is regular consumption of the fruit or its juice. A glass of juice on rare occasion should pose little or no risk—especially if you drink it in the morning, say, and take your simvastatin in the evening (the best time to take many statins, since the body makes most cholesterol at night).

By the way, three statins are not affected by grapefruit—pravastatin (brand name Pravachol), rosuvastatin (Crestor), and fluvastatin (Lescol)—since they are metabolized differently by the body

Q: Is coconut water healthy?

A: Yes. You might find it refreshing, too. Coconut water (or juice) is the thin liquid found naturally inside young green coconuts —not to be confused with creamier coconut milk, which is made from the white flesh of older coconuts (the water is absorbed into the flesh as the coconut ripens). It’s popular in the tropics and, if the coconut is freshly opened, is a source of safe water. You can find pasteurized coconut water at many health-food stores and markets.

Coconut water provides potassium (about 600 milligrams per cup, more than a banana), along with some calcium, magnesium, sodium, and sugar. According to the USDA, it may have some fiber and even a little protein and vitamin C. Some companies promote coconut water as a sports drink, since it can replenish electrolytes (such as sodium and potassium) lost during sustained exercise.

It’s debatable whether the saturated fat in coconut milk is bad for you, but coconut water has no fat to worry about. And it’s far lower in calories than coconut milk (about 45 versus 500 per cup). Some coconut water has added sweeteners or is mixed with fruit purée, however, which adds calories.

Because coconut water has the same electrolyte balance as blood (it’s "isotonic"), it has been called "the fluid of life." During World War II, it was used as a substitute for intravenous plasma. But don’t believe claims that it can control diabetes, fight viruses, speed metabolism, treat kidney stones, smooth your skin, stop dandruff, or prevent cancer.

UC Berkeley Wellness Letter, December 2007