October 2020 Issue

Supplements: Can Dietary Supplements Help Treat Type 2 Diabetes?
By Densie Webb, PhD, RD
Today’s Dietitian
Vol. 22, No. 8, P. 20

Dietary supplements are advertised to treat practically every disease known to man, many with little to no evidence of benefit. For example, diabetes is a common disease treated by supplementing with herbals, vitamins, minerals, fatty acids, and several other less familiar compounds. As of 2018, approximately 1 out of every 10 Americans was thought to have type 2 diabetes.1 That’s 33 million Americans looking for something to improve their condition. Another 88 million, or 1 in 3, have prediabetes, where blood sugar levels are higher than normal, but not yet high enough to be diagnosed with type 2 diabetes.2

While there are many supplements promoted to alleviate type 2 diabetes and its associated health complications, few have been studied extensively, results are decidedly mixed, and some are more commonly used than others. But not everyone is on board with treating diabetes with supplements.

“Supplements are largely unregulated, and the benefits are unclear,” says Jill Weisenberger, MS, RDN, CDE, CHWC, FAND, owner of Food & Nutrition Solutions by Jill, based in Newport News, Virginia.

When Today’s Dietitian spoke with Toby Smithson, MS, RDN, LD, CDCES, FAND, a certified diabetes educator and founder of DiabetesEveryDay.com, she said, “Ironically, one of my patients asked me yesterday if there were any supplements she could take to keep her blood glucose down.”

Smithson’s position aligns with Weisenberger’s (she doesn’t recommend supplements as a treatment for diabetes). Nevertheless, supplements still are widely used to help prevent or treat type 2 diabetes.

What follows is insight into some of the research conducted on five of the most commonly used and studied supplements positioned as treatments for type 2 diabetes.

Alpha-Lipoic Acid (ALA)
A sulfur-containing acid compound that occurs naturally in both plants and humans, ALA acts as an antioxidant. It also functions as an essential part of energy and amino acid metabolism.3 ALA supplements have been used to boost the body’s ability to use the insulin it produces normally to lower blood sugar in people with type 2 diabetes.

A 2014 study in mice found that giving 100 or 200 mg/kg per day of ALA, while on a high-fat diet, resulted in significantly reduced hyperglycemia and insulin resistance, similar to when mice were given the oral diabetes medication metformin.4

In a small study, 12 subjects with obesity and type 2 diabetes (average age 53) were given 600 mg ALA twice a day for four weeks and were compared with 12 subjects with normal glucose tolerance not given the supplement. Supplementation with oral ALA increased peripheral insulin sensitivity in the subjects with type 2 diabetes.5 In a recent systematic review and meta-analysis of studies on ALA supplementation, three studies examined postprandial blood glucose in subjects with uncomplicated diabetes and found no difference between the supplemented and unsupplemented groups.6

ALA also has been used as a treatment for diabetic neuropathy, nerve damage that occurs in over 50% of patients with diabetes, most often in the legs and feet, as a result of high blood sugar levels. A four-month study of 20 patients with type 2 diabetes, some with good glycemic management and some with poor glycemic management, found that ALA was significantly more effective at alleviating diabetic neuropathy symptoms in those with good glycemic control. In the study, ALA was given as an infusion of 600 mg for 21 days, 600 mg was taken orally for three months, and a maintenance dose of 300 mg per day was prescribed.7

Both animal and human studies suggest ALA supplements may reduce cardiovascular risk factors in type 2 diabetes, possibly by reducing oxidative stress.8-10 Human studies found 600 mg per day to improve systemic inflammation.

A 2020 study found that serum chromium levels were lower in patients with type 2 diabetes who had higher serum glucose levels.11 Data from the 2012 National Health and Nutrition Examination Survey (NHANES) showed that the odds of having type 2 diabetes were lower in those who took supplements containing chromium.12 But surveys such as NHANES don’t prove cause and effect.

However, the evidence for chromium supplements and type 2 diabetes is decidedly mixed. A 2016 review of 14 randomized controlled studies found that the source of chromium determined whether the mineral lowered fasting plasma glucose. Doses varied greatly among the studies, making comparisons difficult. Nevertheless, compared with controls, chromium chloride, chromium yeast, and chromium picolinate (the most common form found in supplements) showed no effect. On the other hand, brewer’s yeast, which is rich in chromium, showed a statistically significant decrease in fasting plasma glucose.13

A pooled analysis of 28 studies suggested that chromium supplementation with chromium chloride and chromium picolinate reduced fasting plasma glucose, HbA1c, and triglycerides in subjects with type 2 diabetes.14 Again, dosing varied, making conclusions difficult. However, the authors suggested that chromium supplementation might be a candidate as an adjunct to pharmacological management in patients with type 2 diabetes.

A systematic review and meta-analysis of 22 studies of chromium supplementation found that supplementation of more than 200 mcg per day improved glycemic control. Supplementation also improved triglycerides and HDL cholesterol levels.15

An earlier review of 20 randomized controlled trials of chromium supplementation in patients with type 2 diabetes concluded that the existing evidence at that time showed limited efficacy and that there was little rationale to recommend chromium supplements for glycemic control in patients with type 2 diabetes.16

Data on combination supplements that contain chromium is limited and inconclusive. However, one four-month study of 62 subjects with elevated fasting blood glucose who received a dietary supplement containing chromium, cinnamon, and carnosine found that subjects with overweight and obesity experienced decreased fasting plasma glucose and increased fat-free mass.17 The researchers suggested that the combination supplement might be helpful in the prevention of diabetes.

Cinnamon has been used for centuries both as a spice and as a remedy for a wide variety of medical conditions, including bronchitis, gastrointestinal problems, loss of appetite, and diabetes.18 However, it’s promoted most widely for treating type 2 diabetes. Several studies have been conducted giving cinnamon supplements to mice with diabetes or to people with type 2 diabetes.

But while some studies show cinnamon’s benefit for reducing fasting blood glucose when used in addition to changes in diet and lifestyle—and sometimes in addition to hypoglycemic medications—most human studies have demonstrated only modest improvements, if any at all.

In 2004, one study demonstrated that cinnamon extract lowered blood glucose in mice with diabetes in a dose-dependent manner when given extremely high doses (200 mg/kg had the greatest effect).19

Most studies using cinnamon have been conducted overseas. However, in 2007, the first US study to evaluate the effects of cinnamon on blood glucose in patients with type 2 diabetes found that cinnamon taken at a dose of 1 g per day for three months produced no significant changes in fasting glucose in 30 subjects taking the supplement.20

In a recent randomized controlled trial, researchers gave 140 patients with type 2 diabetes either cinnamon bark powder (500 mg) or a placebo twice a day for three months.21 While researchers saw improvements in fasting plasma glucose, improvements were significantly greater in patients with a higher baseline BMI (27 kg/m2). In an earlier randomized controlled study, 105 patients with type 2 diabetes who were given 1 g of cinnamon per day for 90 days saw improvement in fasting blood glucose.22

Several review papers and meta-analyses have been published, providing mixed conclusions.23-25 One recent meta-analysis of 16 randomized controlled studies found that cinnamon supplements reduced fasting blood glucose in patients with type 2 diabetes and those with prediabetes compared with placebo. However, the researchers emphasized that the studies varied considerably regarding the type of subjects included, the length of the studies, whether the subjects took oral medications, and the dosages of the cinnamon supplement.26 Moreover, there are many types of cinnamon, a factor seldom identified in studies that could affect outcomes.18

Fenugreek has a long history of medical use in Ayurvedic and Chinese medicine. Recently, preliminary animal and human trials suggest it has the potential to lower blood sugar levels. A meta-analysis of 10 such studies examining the effect of fenugreek on glycemia found that fenugreek seeds (about 5 g/day) significantly reduced fasting blood glucose, two-hour glucose, and HbA1c.27

In one study, researchers gave 10 g of fenugreek seeds daily for six months to 60 patients with type 2 diabetes who were taking either insulin or oral hypoglycemic agents as they followed a prescribed diet and regular exercise. The researchers found that by the fourth month there was a synergistic effect of diet, exercise, and fenugreek, resulting in a trend toward reduced fasting blood glucose and HbA1c, although the downward trend wasn’t significant.28

Research also has suggested that fenugreek may help delay or prevent diabetes from developing initially. A three-year randomized controlled trial found that supplementing with 10 g fenugreek per day reduced the conversion of prediabetes to diabetes among 66 subjects. The control group with prediabetes had a 4.2 times higher risk of developing diabetes during the study compared with those taking fenugreek supplements.29

Animal studies suggest that fenugreek seed may work to aid diabetes in several ways, including slowing digestion of carbohydrates, reducing gastrointestinal absorption of glucose, and stimulating glucose uptake in peripheral tissues.30

While there have been several human trials conducted to test the efficacy of fenugreek in type 2 diabetes, most haven’t been well controlled, were short-term, or involved small numbers of subjects.

Berberine is the active component of an ancient Chinese herb used to treat diabetes.31 According to Jim Painter, PhD, RDN, emeritus professor at Eastern Illinois University in Charleston, Illinois, “There are an amazing number of clinical trials with berberine, but they are usually small.”

A systematic review and meta-analysis of 14 studies concluded that berberine exhibited efficacy comparable to that of conventional oral hypoglycemic agents.32 However, doses given to subjects varied among the studies and the authors of the study emphasized that the quality of the studies was low, making it difficult to develop recommendations for berberine.

Berberine also has been shown to lessen oxidative stress and inflammation, both of which can result from diabetes and that can worsen the progression and complications of the disease.33

Despite the findings, Barbie Cervoni, MS, RD, CDCES, CDN, former advanced nutrition coordinator for the diabetes alliance at Mount Sinai Diabetes and Cardiovascular Alliance in New York, says, “It’s important for people to understand that taking a supplement does not replace a medication and that too much can cause adverse side effects.”

Bottom Line
Given the lack of conclusive evidence from randomized controlled trials, controversy lingers regarding the potential benefits or risks of any one dietary supplement to prevent the development of type 2 diabetes or to help manage blood glucose levels. In fact, the American Diabetes Association says, “There is insufficient evidence to support the routine use of herbals and micronutrients, such as cinnamon, curcumin, vitamin D, or chromium, to improve glycemia in people with diabetes.”

When Painter was asked whether he supported the ADA’s recommendation not to take supplements for diabetes, he said, “They’re not wrong, just conservative. There is almost nothing in nutrition where there is clear evidence of benefit—unless it’s a deficiency disease—and these supplements are no exception. When you first hear the information [about supplements], you should think, ‘That’s interesting,’ rather than make an immediate decision.”

Painter recommends dietitians do their own digging and find out whether positive study findings have been reproducible in the general public.

— Densie Webb, PhD, RD, is a writer, editor, and industry consultant based in Austin, Texas.


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