Keeping a Lid on Blood Sugar.

DO SUPPLEMENTS WORK?

High cholesterol? Aching joints? Swollen prostate? Flagging sex life? If you can find over-the-counter supplements that claim to treat those problems, it's no surprise to see pills to help lower blood sugar. Here's the evidence behind nine supplements that are often touted as tools to help keep blood sugar in check. Just keep in mind that much of the research has been done in people who have diabetes or whose blood sugar is already high. The results may or may not apply to people who want to keep their normal--or slightly elevated--blood sugar from rising.

* Garlic

Garlic is used "to stabilize blood sugar levels," according to www.alternativeDr.com, a Web site on alternative health care.

That's a load of bunk. According to a national panel of experts that reviewed all 12 of the studies that have been done on garlic and blood sugar, "Garlic preparations had no clinically significant effect on blood glucose [blood sugar] in persons with or without diabetes." The authors of the comprehensive review, which was issued last year by the U.S. government's Agency for Healthcare Research and Quality, included authorities on botanical medicines.(1)

(1) www.ahrq.gov/clinic/garlicsum.htm.

* Vanadium 

"Very large doses of vanadyl sulfate, a form of the mineral vanadium, can lower blood sugar levels by mimicking insulin action in people with type 2 diabetes," says the USDA's Hank Lukaski.(1) But that dosage--100 to 300 mg of vanadyl sulfate a day--delivers 1,700 times more vanadium than the average person gets from his or her food. It's also 20 to 50 times the "Upper Limit" (UL) for vanadium recommended by the National Academy of Sciences, which is based on studies showing that vanadium causes kidney damage in animals. And it caused abdominal cramps and loose stools in some of the volunteers with diabetes who took it. What's more, "even at the large doses, vanadyl sulfate does not dramatically improve insulin sensitivity or glucose control," says Allison Goldfine of the Harvard Medical School.

Until companies find safer forms of vanadium (they're looking), pass it up.

(1) Metabolism 49: 400, 2000.

* Chromium

For insulin to function properly and keep blood sugar levels under control, our bodies need chromium, which we get from food. But can taking more of the metal help bring high blood sugar levels down and keep them there?

"One major published study shows that it can," says mineral researcher Hank Lukaski of the U.S. Department of Agriculture's Human Nutrition Research Center in Grand Forks, North Dakota. In that study, of 155 people in China with type 2 diabetes, blood sugar fell by close to 30 percent in the 52 who took 1,000 micrograms of chromium picolinate (a well-absorbed form) every day for four months. The 53 who took 200 micrograms a day had no lower blood sugar levels than those who took a (look-alike but chromium-free) placebo.(1) (Only one study has looked at whether another popular form--a combination of chromium and the B-vitamin nicotinate--lowers blood sugar. It didn't.)

But 1,000 micrograms is more than 25 times the amount that scientists say healthy people seem to need every day. "We don't know how safe such large amounts are when taken over a long period," says Lukaski. Although there have been no side effects in human studies, several test-tube studies have suggested that chromium picolinate may damage DNA. And Lukaski and his colleagues have new, not-yet-published research showing that taking chromium picolinate can cause mood changes. Because there's too little reliable information, the National Academy of Sciences says that it can't set an upper limit on the amount of chromium that's safe to take over a long period of time.

Meanwhile, even the largest manufacturer of chromium picolinate, AMBI Inc. of Purchase, New York, advises people with diabetes to use its product only under a physician's supervision. Too bad that warning is on the company Web site and not on supplement bottle labels, where shoppers can see it.

(1) Diabetes 46: 1786, 1997.

* Lipoic Acid

"Lipoic acid has three potential benefits in diabetes," says Ishwarlal Jialal of the University of Texas Southwestern Medical Center in Dallas. "In European studies, taking 600 mg twice a day improved the symptoms of diabetic neuropathy, which is a complication that's often ignored."(1) (Neuropathy is the numbness or tingling felt by people whose diabetes has caused nerve damage to their feet or hands.) "If I had diabetic neuropathy, I would take lipoic acid for want of anything better," says Jialal. Researcher Philip Lowe of the Mayo Clinic in Rochester, Minnesota, recently started a four-year study of lipoic acid. "Since diabetic neuropathy develops very slowly, it's essential to study its effect over a long period of time," he says.

The second possible benefit: lipoic acid may lower blood sugar levels. "The animal research is fantastic," says Jialal, "but we're nowhere near establishing that it can do this in people."

"The third potential benefit of lipoic acid is as an antioxidant to reduce oxidative stress and inflammation, which are increased in the diabetic," says Jialal. "It could be valuable for diabetics, but more research is needed."

Lipoic acid is produced naturally in the body, and no major side effects have been reported.

(1) Diabetic Medicine 16: 1040, 1999.

* Magnesium

"Two large U.S. studies have found that people with lower levels of magnesium in their blood or their diets are more likely to develop type 2 diabetes than people with higher levels," says Linda Kao, an epidemiologist at the Johns Hopkins School of Public Health in Baltimore.(1,2) And lower-than-normal levels of magnesium are typically found in people with diabetes.

But that doesn't mean that taking magnesium pills will help control blood sugar levels. At least five studies have tested magnesium supplements for up to 16 weeks in more than 225 people with type 2 diabetes. None found any effect on blood sugar.

It's still possible that magnesium may help prevent diabetes. To play it safe, make sure you get the Daily Value (DV) for magnesium (400 mg for adults) from food and, if necessary, a supplement.

(1) Journal of Clinical Epidemiology. 48: 927, 1995.

(2) American Journal of Clinical Nutrition. 55: 1018, 1992.

* Ginseng 

"Taking three grams of American ginseng with meals can lower blood sugar by 20 percent," Andrew Weil tells visitors to his popular alternative medicine Web site, www.drweil.com. "This news comes as something of a breakthrough," he adds.

Actually, it's more like a ripple. In two small studies at the University of Toronto, a total of 19 people with type 2 diabetes who took a single heavy dose (three grams) of American ginseng had lower blood glucose levels for several hours after eating a meal.(1,2)

"Since then, we've found that a smaller dose of one gram works, and that taking three grams every day for eight weeks also kept sugar levels lower," says researcher Vladimir Vuksan.

But questions remain: All four of Vuksan's studies used a special batch of American ginseng extract that isn't currently on the market. "We've seen something," says Vuksan, "but we don't know yet whether other kinds of ginseng--or other extracts of American ginseng--would produce the same results."

(1) Archives of Internal Medicine 160: 1009, 2000.

(2) Diabetes Care 23: 1221, 2000.

Other Supplements

Here's the evidence on three other dietary supplements that some people take to help lower their blood sugar.

* Fenugreek. It's been used as both a spice and a medicine for thousands of years in the Middle East and India. Several small pilot studies have suggested that five to 100 grams of fenugreek seeds eaten every day may lower blood glucose levels in both type 1 and type 2 diabetics. That's far more fenugreek than dietary supplements contain.

Prostaglandins Leukot. Essent. Fatty Acids 56: 379, 1997.

* Fish Oil, Fish oil supplements lower triglycerides (that's good) and raise LDL cholesterol (that's bad), but they have no effect on blood sugar levels, according to a recent meta-analysis that pooled the results of 18 studies on a total of 823 type 2 diabetics.

Diabetes Care 23: 1407, 2000.

* Gymnema. The leaves of this tropical plant have been traditionally used in India to treat diabetes, but there are no good studies comparing it to a placebo in type 2 diabetics.