Archive 2005 2006 2007 2008

Q: Should I avoid taking my calcium supplement with my morning coffee? I heard that caffeine interferes with calcium absorption.

A: Don’t worry about the timing. Caffeine slightly reduces calcium absorption, but this is not a problem if you get adequate calcium, according to Dr. Robert Heaney, a noted calcium researcher at Creighton University in Nebraska. As little as one to two tablespoons of milk is enough, he says, to offset any potential effects of the caffeine.

Though a few studies have linked caffeine-containing beverages to reduced bone density and increased fractures, this is seen mainly in people with low calcium intake. That is, the combination of high caffeine and low calcium seems to be harmful to bones, not caffeine alone.

Rather than worry about calcium-caffeine interactions, just be sure to get enough calcium from food and/or supplements: 1,000 milligrams a day for people age 19 to 50, and 1,200 milligrams for those over 50. (And get enough vitamin D, which works with calcium—we advise 800 to 1,000 IU for most people.) Keep in mind that many substances interfere with the absorption of nutrients in general, and dietary recommendations take such factors into account.

Q: Can FRS, the energy drink endorsed by Lance Armstrong, improve my athletic performance?

A: Its main ingredient, the antioxidant quercetin, looks promising in some studies. But there’s little evidence to support claims that FRS enhances exercise/work performance, reduces recovery time, fights fatigue, or neutralizes free radicals produced by exercise.

FRS (for Free Radical Scavenger) contains 325 milligrams of quercetin (the average diet provides 25 to 50 milligrams a day), plus green tea catechins (also antioxidants), B vitamins, C, and E (said to enhance the effectiveness of quercetin), and a little caffeine. The recommended “dose” is two 11.5-ounce cans (or four soft chews) a day. Besides Lance Armstrong, who is on the board of the company, a score of well-known athletes and coaches have endorsed the product.

In small studies by Dr. David Nieman, a sports nutrition researcher at Appalachian State University in North Carolina, high doses of quercetin reduced infections and boosted vigilance in athletes, even though no changes were seen in immune markers, inflammation, or free radical damage.

But, says Dr. Nieman, the claims made for FRS are based more on speculation than science. Only one study on the actual product has been published. It found that two cans of FRS a day for six weeks improved performance in a small group of elite cyclists—though a formulation without quercetin resulted in some improvements too.

If you’re a recreational exerciser, any effect of FRS is likely to be insignificant. Besides being unproven, it costs about $2 a can and has 140 calories (though low-calorie versions are available). If you’re looking for quercetin and other antioxidants, eat more fruits and vegetables. Good quercetin sources include apples, onions, broccoli, blueberries, red grapes, red wine, and tea.

Q: In August you said that maté has been linked to esophageal cancer, possibly because of the hot temperature at which the herbal tea is consumed. What about coffee and other hot drinks?

A: Studies dating to the 1930s have linked scalding-hot beverages (and foods) to both esophageal cancer and pre-cancerous lesions. Chronic exposure of the esophagus to very high temperature can damage tissue in the lining, setting the stage for cellular changes. But this doesn’t mean you should give up coffee or tea. Here’s why:

Most evidence comes from observations of large populations in Asia and South America, where people regularly drink beverages near boiling temperature. Other factors likely play a role as well, such as tobacco and alcohol use. Associations between hot beverages and esophageal cancer are stronger in people who smoke and drink a lot. In addition, something specific to certain beverages or foods (potential cancer-causing compounds in maté, for example, or the high salt content of hot soup) may increase the cancer risk.

The amount consumed may also matter more than temperature alone. In a study from Uruguay in 2003, people who drank more than a liter a day of very hot maté had three times the risk of squamous-cell esophageal cancer as those who drank less than a half-liter at a warm or hot temperature.

Most people in the U.S. don’t drink large amounts of very hot beverages. Moreover, the few studies done in the West have been inconsistent; one in 2001 in the British Journal of Cancer found no link between very hot beverages and esophageal cancer. Keep in mind that some hot beverages, like green tea, have been linked to cancer protection in some (but not all) studies.

To be on the safe side: Don’t make a habit of consuming beverages (and foods) at scalding-hot temperatures—let them cool a little first. The greatest risk factors for esophageal cancer are alcohol and tobacco, so the best way to avoid this disease is to not smoke and to drink moderately, if at all.

Q: My family prefers broccoli stalks to the “flowers.” Which is better for you?

A: All parts of broccoli are good for you. Broccoli is one of the most nutritious vegetables, providing vitamin C (a day’s worth in a cup, chopped), potassium, B vitamins (including folate), even some calcium and iron. Ounce for ounce, the florets and stalks deliver equal amounts of these nutrients, according to the USDA. Broccoli (and other cruciferous vegetables) also contains sulforaphane and other compounds that may protect against certain cancers.

The florets, however, outshine the stalks in beta carotene. And a study in 2006 found that the florets had nearly twice as much sulforaphane. The stalks, on the other hand, have more fiber. Eating all parts of broccoli—even the leaves—is thus a good idea.

Look for broccoli with dark green or purplish (not yellowing) florets. To preserve nutrients, don’t overcook.

UC Berkeley Wellness Letter, September 2008