November 2011 Issue

Taking Diabetes Drugs With Nutritional Supplements
By Sari Harrar
Today’s Dietitian
Vol. 13 No. 11 P. 32

From chromium to magnesium to herbal remedies claiming to stabilize blood sugar levels, over-the-counter diabetes supplements continue to make their way into the hands of patients who want to manage their disease nature’s way.

More than 50% of people with diabetes take nutritional supplements, and those with type 2 diabetes are twice as likely as those with type 1 to experiment with herbal treatments and other nonvitamin, nonmineral pills and capsules, reported Odegard and colleagues in the May/June issue of The Diabetes Educator.

The question is, should they?

More than 80% of diabetes patients are already taking prescription medications to help control their blood sugar. About 58% use one or more oral diabetes drugs, such as sulfonylureas (eg, Glucotrol, Micronase) and meglitinides (eg, Prandin, Starlix) that stimulate insulin release; biguanides (eg, Glucophage, PrandiMet) that decrease glucose production by the liver; alpha-glucosidase inhibitors (eg, Precose, Glyset) that block the breakdown of starches; DPP-4 inhibitors (eg, Januvia, Onglyza) that keep a blood sugar-controlling compound called GLP-1 active longer; and thiazolidinediones (eg, Avandia, ACTOS) that improve insulin action. Another 26% of patients use insulin alone or in combination with oral agents.

Given the number of diabetes patients taking prescription medications, Anna Nabutovskaya, CDE, RD, of Maimonides Medical Center in Brooklyn, N.Y., doesn’t recommend over-the-counter supplements for fear of possible contraindications.

“I’d never advise anyone to take extra chromium or magnesium or to use supplement-level doses of herbal remedies that claim to lower blood sugar,” she says. “One concern is hypoglycemia. A high-dose supplement and a diabetes drug could interact and cause dangerously low blood sugar.” 

Supplement Controversy
When it comes to tablets, capsules, powders, and teas that claim to control blood sugar, RDs and other healthcare practitioners agree that the research doesn’t support the miracle cure reputation many supplements have developed. And with little research available on side effects and potential interactions with oral diabetes medications, insulin, and other drugs diabetes patients often use (such as cholesterol- and blood pressure-lowering agents), not enough is known about long-term safety.

Consider cinnamon, which is emerging as one of the newest herbal remedies for blood sugar control. “A recent meta-analysis1 reported that whole cinnamon or extract lowers fasting blood glucose by about 10 mg/dL,” says Evan Sisson, PharmD, MHA, CDE, an associate professor in the department of pharmacotherapy and outcomes science at Virginia Commonwealth University in Richmond. “While these results are interesting, a patient with an A1c of 8% requires at least a 30 mg/dL lowering of blood glucose to reach the goal A1c of less than 7%. Supplements may be considered as adjunctive agents to prescription treatments for hyperglycemia, not something to be used instead of medications.”

Constance Brown-Riggs, MSEd, RD, CDE, CDN, a national spokesperson for the American Dietetic Association, says the unknowns about cinnamon mean that people with diabetes should steer clear or be extremely cautious.

“We know that using small amounts on food as a spice are safe, but we don’t know the effects of taking larger doses in capsule form every day for months or years,” she says. “We need more research.”

Ongoing research has reframed the picture for some natural remedies. Chromium is a popular supplement for people with type 2 diabetes thanks to 30 years of studies suggesting it may help control blood sugar. But in Western countries, where chromium deficiency is relatively rare, chromium seems to have little benefit.2 The researchers found that 400 mcg of chromium daily for six months didn’t improve blood sugar control in 400 people with type 2 diabetes, though studies conducted in China and India have found improvements.

“A low dose of chromium won’t cause harm, but a high dose could,” Brown-Riggs says. “A multivitamin plus whole grains, broccoli, and other vegetables should give you all you need. At high levels, chromium can harm the kidneys and liver and cause mood disturbances. It also can interfere with medications, including antacids, H2 blockers, proton pump inhibitors, beta blockers, corticosteroids, and nonsteroidal anti-inflammatory drugs.”

Steering Clients in the Right Direction
Because of the possible adverse effects, helping diabetes patients make wise decisions about supplements is critical. You can do the following to help:

Ask creatively—and gently—about supplement use. “People might not think of an herbal remedy or a mineral they’re using as a supplement. Or they may feel nervous talking about what they’re taking,” Brown-Riggs says. “That’s where your skills as an RD and/or CDE come in. Try asking if they take any over-the-counter remedies or supplements or pills. Be open and nonjudgmental so your clients feel comfortable speaking with you about it.”

Determine why clients are interested in supplements. Are they trying to reduce their medication costs? Avoid drugs altogether? Do they think a “natural” substance is better? Did they just see an infomercial or website touting a sugar-controlling remedy?

“Talk about the claims vs. reality,” Brown-Riggs says. “Natural doesn’t always mean better. A hurricane is natural, but it’s deadly. And if there were really a cure for diabetes in a bottle, we’d all be recommending it!”

Start patients with a healthful foundation. “A healthful diet, exercise, and diabetes medications, if needed, come first,” Brown-Riggs says. “Supplements can’t and shouldn’t take the place of those important basics for good health and good blood sugar control.”

If a client wants to use a supplement, recommend starting with a single-ingredient type at a moderate dose, Brown-Riggs suggests. Your client will be more likely to know whether any side effects, interactions, or benefits are related to that particular supplement—something that would be difficult to determine if taking several at once. “Take it for a month. If it’s not helping, stop,” she says.

Suggest a standardized, high-quality product. “A standardized product will have a set amount of active ingredients in every dose,” says Oluwaranti Akiyode, PharmD, an associate professor in the department of pharmaceutical sciences at Howard University in Washington, D.C. “And check the label for the USP [U.S. Pharmacopeia] or seal; it’s a sign that the product meets standards for strength and purity. These steps don’t mean a product is completely safe or that it’s effective, but they ensure quality.”

Nabutovskaya suggests sticking with products made in the United States. “We know what the manufacturing standards are here; we don’t always know with overseas products,” she warns.

Urge continued use of diabetes medications and get the patient’s family doctor or endocrinologist involved. “One of the most dangerous things a person with diabetes can do is to stop taking medications when they start a supplement,” Brown-Riggs says. “Their blood sugar could rise to an unhealthy range very quickly. People with diabetes should continue taking all of their medications. They should also consult first with their doctor about potential interactions, health effects, and about checking their blood sugar more frequently to see if the supplement is lowering glucose levels.”

Advise clients to stop taking the supplement immediately if there are adverse effects, and call the doctor to report any problems.

Five Widely Used Supplements
While putting these strategies into practice is important, they’re only part of the equation. Our expert panel says it’s just as critical to know about the following supplements diabetes patients commonly take and the research behind them, so you can give them the facts.

This tasty spice is emerging as an effective add-on therapy for blood sugar control. In a 2009 study of 109 people with poorly-controlled type 2 diabetes (their average A1c level was 8.4%), those who received 1 g of cinnamon in capsule form daily for 90 days saw A1c levels fall by 0.83% compared with standard care (0.37%).3 The researcher concluded, “This study gives diabetes care providers and diabetes patients an easily accessible, likely safe, and cheap alternative to help treat type 2 diabetes.” In addition, Davis and colleagues concluded that cinnamon can improve fasting blood glucose levels in people with diabetes and prediabetes.1

How it may work: A compound in cassia cinnamon called hydroxychalcone stimulates insulin receptors, improving insulin sensitivity—the key metabolic defect leading to type 2 diabetes.1,4

Recommended dose: 500 mg of cinnamon extract in capsule form taken twice daily3 or 3 to 6 g of powdered cinnamon5 (about 3/4 to 1.2 tsp of ground cinnamon daily) have shown blood sugar-lowering effects in clinical trials.

Potential side effects: Coumarin, also found in cinnamon, may worsen liver damage.4 Nabutovskaya warns that higher doses in capsule form could lead to contact dermatitis.

Bitter Melon
Widely used in the cuisines of Africa, Asia, India, and South America,6 extracts of bitter melon fruit (Momordica charantia) are sold in capsule form to maintain healthy blood sugar levels. Yet according to the National Institutes of Health’s (NIH) National Center for Complementary and Alternative Medicine, there’s limited research supporting this claim.7

How it may work: In a study by Tan and colleagues, published in 2008 in Chemistry & Biology, researchers isolated bitter melon compounds called cucurbitane triterpenoids that activate an enzyme that encourages muscle cells to take up blood sugar.

Recommended dose: Bitter melon is used as a vegetable, juice, tea, or taken in capsules. Typical dose is 50 to 100 mL (3 to 6 T) per day.

Potential side effects: Bitter melon may cause gastrointestinal distress and allergic reactions in people with allergies to melons.4

An ancient medicinal herb, fenugreek (Trigonella foenum-graecum) smells and tastes like maple syrup. Several small studies suggest that fenugreek seeds may help reduce blood sugar in people with diabetes, according to the NIH.7

How it may work: Rich in fiber and compounds called saponins, fenugreek seems to slow down carbohydrate absorption after a meal and improve insulin sensitivity.6

Recommended dose: Available as a tea and in capsule form, a typical dose is 5 to 100 g/day.4

Potential side effects: Fenugreek may cause gas, bloating, and diarrhea. It may interact with blood-thinning drugs such as warfarin (Coumadin).4

Vitamin D
Healthy people who took 500 IUs or more of vitamin D daily were 13% less likely to develop type 2 diabetes than those getting less than 200 IUs per day, according to a September review by Mitri and colleagues published in the European Journal of Clinical Nutrition. But can getting enough vitamin D improve blood sugar control for people who already have type 2 diabetes?

In a 2007 review in The Journal of Clinical Endocrinology & Metabolism, Pittas and colleagues reported that vitamin D plus calcium could help support better blood sugar control. “Low vitamin D has been associated with poor glycemic control in some early research, but we don’t know yet if taking it really helps control blood sugar or how it may work,” says Akiyode, who researches the role of vitamin D in the prevention, treatment, and management of diabetes.

Does that mean everyone with diabetes should take a supplement? Risk factors for a vitamin D deficiency include dark skin, older age, obesity, and limited sun exposure or the use of sunscreens and cover-ups outdoors.8 The National Center for Health Statistics estimates that one in three Americans don’t get enough vitamin D.9

How it may work: Vitamin D and calcium seem to improve insulin sensitivity, but researchers aren’t sure of the exact mechanism of action.

Recommended dose: According to the Institute of Medicine, adults should get 1,000 mg of calcium daily up to age 50 and 1,200 mg daily thereafter, along with 600 IUs of vitamin D daily up to age 70 and 800 IUs thereafter.10 For optimal bone density, the National Osteoporosis Foundation recommends up to 800 IUs of vitamin D daily until age 50 and up to 1,000 IUs thereafter. Up to 4,000 IUs is even considered safe.10

Some experts recommend a blood test to check vitamin D levels before people begin taking supplements; some may need prescription-strength doses for a short time to boost levels.

“Have your blood rechecked to see if levels have increased,” Akiyode recommends. “If you just need an over-the-counter [vitamin] D supplement, choose D3—it’s closer to the type your body makes and is more bioavailable than D2.”

Potential side effects: There’s some evidence that taking high doses of vitamin D for long periods could cause weight loss, heart rhythm problems, and even damage to the heart, blood vessels, and kidneys.8

One in four people with diabetes may have low blood levels of magnesium, reported a 1996 review by Tosiello in the Archives of Internal Medicine. According to the NIH’s Office of Dietary Supplements, diabetes may increase magnesium requirements for two reasons: Both poorly controlled blood sugar and the use of blood pressure-lowering diuretic drugs can lead to loss of excess magnesium in urine.11

But can magnesium help control blood sugar? The research is contradictory: In one study by Rodríguez-Morán and Guerrero-Romero published in Diabetes Care in 2003, people with type 2 diabetes and low magnesium levels who took oral magnesium chloride daily for 16 weeks saw improvements in their A1c results. But other research has found no benefit.12

How it may work: Magnesium plays a role in the transport of glucose into cells and may improve insulin sensitivity.6

Recommended dose: The recommended dietary allowances for magnesium are 400 mg per day for men aged 19 to 30; 420 mg for men aged 30 and older; 310 mg for women aged 19 to 30; and 320 mg for women aged 30 and older. A multivitamin containing about 100 mg of magnesium plus several servings of whole grains and green vegetables may supply all the magnesium needed.13 According to the Office of Dietary Supplements, however, people with diabetes could benefit from magnesium supplementation. The tolerable upper intake for magnesium in supplement form is 350 mg per day.11

Possible side effects: High-dose supplements may cause diarrhea, cramping, muscle weakness, breathing problems, and a low heart rate.11

— Sari Harrar is an award-winning freelance writer specializing in health, medicine, and science. Her articles appear in national magazines including O, The Oprah Magazine; Reader’s Digest; Good Housekeeping; Better Homes and Gardens; and Organic Gardening.


1. Davis PA, Yokoyama W. Cinnamon intake lowers fasting blood glucose: Meta-analysis. J Med Food. 2011;14(9):884-889.

2. Kleefstra N, Houweling ST, Bakker SJ, et al. Chromium treatment has no effect in patients with type 2 diabetes in a Western population: A randomized, double-blind, placebo-controlled trial. Diabetes Care. 2007;30(5):1092-1096.

3. Crawford P. Effectiveness of cinnamon for lowering hemoglobin A1C in patients with type 2 diabetes: A randomized, controlled trial. J Am Board Fam Med. 2009;22(5):507-512.

4. Campbell AP. Diabetes and dietary supplements. Clin Diabetes. 2010;28(1):35-39.

5. Hlebowicz J, Hlebowicz A, Lindstedt S, et al. Effects of 1 and 3 g cinnamon on gastric emptying, satiety, and postprandial blood glucose, insulin, glucose-dependent insulinotropic polypeptide, glucagon-like peptide 1, and ghrelin concentrations in healthy subjects. Am J Clin Nutr. 2009;89(3):815-821.

6. Yeh GY, Eisenberg DM, Kaptchuk TJ, Phillips RS. Systematic review of herbs and dietary supplements for glycemic control in diabetes. Diabetes Care. 2003;26(4):1277-1294.

7. National Institutes of Health National Center for Complementary and Alternative Medicine. Dietary supplements and type 2 diabetes. Available at: Last accessed September 2011.

8. National Institutes of Health Office of Dietary Supplements. Dietary supplement fact sheet: Vitamin D. Available at: Last accessed September 2011.

9. Centers for Disease Control and Prevention National Centers for Health Statistics. Vitamin D status: United States, 2001–2006. NCHS Data Brief. Number 59. Available at: Last accessed September 2011.

10. Institute of Medicine of the National Academies. Dietary Reference Intakes for calcium and vitamin D. November 2010. Available at: Last accessed September 2011.

11. National Institutes of Health Office of Dietary Supplements. Dietary supplement fact sheet: Magnesium. Available at: Last accessed September 2011.

12. de Lourdes Lima M, Cruz T, Pousada JC, Rodrigues LE, Barbosa K, Canguçu V. The effect of magnesium supplementation in increasing doses on the control of type 2 diabetes. Diabetes Care. 1998;21(5):682-686.

13. Linus Pauling Institute Micronutritient Information Center. Magnesium: Linus Pauling Institute recommendation. Available at: Last accessed September 2011.