Type 1 diabetics will need to be on insulin therapy for life, although the supplements mentioned in this section may help offset some of the complications caused by diabetes (e.g., reduced antioxidant capacity and glycation) as well enhance glucose metabolism. Type 2 diabetics can counteract the progression of their disease by improving insulin sensitivity, enhancing glucose metabolism, and attempting to mitigate the complications of diabetes. The following supplements have been shown to improve blood sugar control or limit diabetic damage:
Lipoic acid. As a powerful antioxidant, lipoic acid positively affects important aspects of diabetes, including blood sugar control and the development of long-term complications such as disease of the heart, kidneys, and small blood vessels (Jacob 1995, 1999; Kawabata 1994; Melhem 2002; Nagamatsu 1995; Song 2005; Suzuki 1992).
Lipoic acid plays a role in preventing diabetes by reducing fat accumulation. In animal studies, lipoic acid reduced body weight, protected pancreatic β-cells from destruction, and reduced triglyceride accumulation in skeletal muscle and pancreatic islets (Doggrell 2004; Song 2005).
Lipoic acid has been approved for the prevention and treatment of diabetic neuropathy in Germany for nearly 30 years. Intravenous and oral lipoic acid reduces symptoms of diabetic peripheral neuropathy (Ametov 2003). Animal studies have suggested that lipoic acid is more effective when taken with gamma-linolenic acid (GLA) (Cameron 1998; Hounsom 1998).
Diabetes also damages deep nerves that control vital organs, such as the heart and digestive tract. In a large clinical trial, diabetics (with symptoms caused by nerve damage affecting the heart) showed significant improvement without significant side effects from 800 mg oral lipoic acid daily (Ziegler 1997a,b).
Biotin. Biotin enhances insulin sensitivity and increases the activity of glucokinase, the enzyme responsible for the first step in the utilization of glucose by the liver. Glucokinase concentrations in diabetics are very low. Animal studies have shown that a high biotin diet can improve glucose tolerance and enhance insulin secretion (Zhang 1996; Furukawa 1999).
Carnitine. An extensive body of literature supports the use of carnitine in diabetes (Mingrone 2004). Carnitine lowers blood glucose and HbA1c levels, increases insulin sensitivity and glucose storage, and optimizes fat and carbohydrate metabolism. Carnitine deficiency is common in type 2 diabetes. In a large human trial, acetyl-L-carnitine helped prevent or slow cardiac autonomic neuropathy in people with diabetes (Turpeinen 2005).
Carnosine. Carnosine is a glycation inhibitor that has been shown to exhibit protective effects against diabetic nephropathy and reduce the formation of AGEs (Janssen 2005; Yan 2005).
Studies show that diabetics’ cells have lower-than-normal carnosine levels, similar to levels in older adults (McFarland 1994). Carnosine lowers elevated blood sugar levels, limits oxidant stress and elevated inflammation, and prevents protein cross-linking in diabetics and otherwise healthy aging adults (Jakus 2003; Hipkiss 2005; Nagai 2003; Hipkiss 2001; Aldini 2005). Additionally, carnosine works ‘behind the scenes’ to offer the following protection (for diabetics) against the physiological destruction caused by high blood sugar:
Chromium. Chromium is an essential trace mineral that plays a significant role in sugar metabolism. Chromium supplementation helps control blood sugar levels in type 2 diabetes and improves metabolism of carbohydrates, proteins, and lipids. Several studies have shown encouraging results from chromium supplementation:
Coenzyme Q10. Coenzyme Q10 (CoQ10) improves blood sugar control, lowers blood pressure, and prevents oxidative damage caused by disease. In a controlled human trial, type 2 diabetics given 100 mg CoQ10 twice daily experienced improved glycemic control as measured by lower HbA1c levels and blood pressure (Hodgson 2002). In a separate study, CoQ10 improved blood flow in type 2 diabetics, an outcome attributed to CoQ10’s ability to lower vascular oxidative stress (Watts 2002). In a third study, improved blood flow correlated with decreased HbA1c (Playford 2003).
In animal studies, CoQ10 quenched free radicals, improved blood flow, lowered triglyceride levels, and raised HDL levels, suggesting a role for CoQ10 in preventing and managing complications of diabetes (Al-Thakafy 2004). Animal studies have also shown that CoQ10 levels are depleted by diabetes (Kucharska 2000).
Dehydroepiandrosterone. Recent studies have yielded very encouraging results supporting dehydroepiandrosterone (DHEA) supplementation in diabetics. DHEA has been shown to improve insulin sensitivity and obesity in human and animal models (Yamashita 2005). Although its mechanism of action is poorly understood, it is thought that DHEA improves glucose metabolism in the liver (Yamashita 2005).
Animal studies have also demonstrated that DHEA increases β-cells on the pancreas, which are responsible for producing insulin (Medina 2006).
In humans, DHEA levels are sensitive to elevated glucose; thus, higher glucose levels tend to be associated with decreased DHEA levels (Boudou 2006). One proposed mechanism of action in humans is linked to DHEA’s metabolism into testosterone. DHEA is an adrenal hormone that can be converted into either testosterone or estrogen. Studies have shown that testosterone improves insulin sensitivity in men, suggesting that DHEA’s conversion into testosterone may be responsible for its beneficial effects in improving insulin sensitivity (Kapoor 2005).
Essential fatty acids. In human experiments, omega-3 fatty acids lowered blood pressure and triglyceride levels, thereby relieving many of the complications associated with diabetes. In animals, omega-3 fatty acids cause less weight gain than other fats do; they have also been shown to have a neutral effect on LDL, while raising HDL and lowering triglycerides (Petersen 2002). There are two types of essential fatty acids:
Fiber. Eating a diet rich in high-fiber foods prevents and reduces the harm caused by chronically elevated blood glucose.
One study reported the results of diabetic individuals consuming a diet supplying 25 grams of soluble fiber and 25 grams of insoluble fiber (about double the amount currently recommended by the American Diabetes Association). The fiber was derived from foodstuffs, with no emphasis placed on special or unusual fiber-fortified foods or fiber supplements. A high-fiber diet reduced blood glucose levels by an average of 10 percent (Chandalia 2000).
Fiber is also valuable because it produces a feeling of satiety, reducing the desire to overeat. Because high-fiber foods are digested more slowly than other foods, hunger pangs are forestalled. For the most part, fibrous foods are healthful (nutrient dense and low-fat).
Fiber should be added slowly, gradually replacing low-fiber foods, for the following reasons: (1) insulin and prescription drugs may have to be adjusted to accommodate lower blood glucose levels, and (2) without a gradual introduction of the new material, intestinal distress could occur, including bloating, flatulence, and cramps.
Some individuals prefer to bolster fiber volume by adding supplemental fiber in the form of pectin, gums, and mucilages to each meal. Calculate the amount of fiber gained from foodstuffs and supplement with enough to compensate for shortfalls. Monitor blood glucose levels closely to assess gains and adjust oral or injectable hypoglycemic agents.
Propolmannan. Specially processed, propolmannan is a polysaccharide fiber derived from a plant (Amorphophallus konjac) that grows only in the remote mountains of Northern Japan.
Used throughout Asia as a source of bulk in the diet, it creates a viscous barrier that impedes carbohydrate digestion, suppressing postprandial (after-meal) blood sugar surges. Propolmannan also slows "gastric emptying"—the passage of food from the stomach into the small intestine—impeding carbohydrate overexposure in the digestive tract. Propolmannan's power to safely suppress postprandial glucose surges has generated compelling results. In a group of 72 diabetics given konjac foods, postprandial glucose levels fell by an average of 84.6% (Huang 1990).
In placebo-controlled human studies, those taking propolmannan before meals lost 5.5 to 7.92 pounds after eight weeks without changing their diets. The placebo groups in these studies showed no significant weight loss. The propolmannan groups also showed reductions in blood lipid/glucose levels (Walsh 1984; Biancardi 1989).
Flavonoids. Flavonoids are antioxidants that help reduce damage associated with diabetes. In animal studies, quercetin, a potent flavonoid, decreased levels of blood glucose and oxidants. Quercetin also normalized levels of the antioxidants superoxide dismutase, vitamin C, and vitamin E. Quercetin is more effective at lower doses and ameliorates the diabetes-induced changes in oxidative stress (Mahesh 2004).
Magnesium. Diabetics are often deficient in magnesium, which is depleted by medications and the disease process (Eibl 1995; Elamin 1990; Tosiello 1996). One double-blind study suggested that magnesium supplementation enhanced blood sugar control (Rodriguez-Moran 2003).
N-acetylcysteine. N-acetylcysteine (NAC) is a powerful antioxidant that is used to treat acetaminophen overdose. Among diabetic rats, it has also demonstrated the ability to protect the heart against endothelial damage and oxidative stress that is associated with heart attacks among diabetics. In one study, NAC was able to increase the availability of nitric oxide in diabetic rats, thus improving their blood pressure as well as reducing the level of oxidative stress in their hearts (Xia 2006). In a human study examining the effects of broad-based antioxidants, NAC, in addition to vitamins C and E, was able to reduce oxidative stress after a moderate-fat meal (Neri 2005).
Silymarin. In animal studies, silymarin was shown to improve insulin levels among induced cases of diabetes (Soto 2004). A small, controlled clinical study evaluated type 2 diabetics with alcohol-induced liver failure (Velussi 1997). Those receiving 600 mg silymarin daily experienced a significant reduction in fasting blood and urine glucose levels. Fasting glucose levels rose slightly during the first month of supplementation but declined thereafter from an average of 190 mg/dL to 174 mg/dL. As daily glucose levels dropped (from an average of 202 mg/dL to 172 mg/dL), HbA1c also substantially decreased. Throughout the course of treatment, fasting insulin levels declined by almost one-half, and daily insulin requirements decreased by about 24 percent. Liver function improved. A lack of hypoglycemic episodes suggests silymarin lowered as well as stabilized blood glucose levels.
Vitamin B3. Vitamin B3 (niacin) is required for the proper function of more than 50 enzymes. Without it, the body is not able to release energy or make fats from carbohydrates. Vitamin B3 is also used to make sex hormones and other important chemical signal molecules.
In the past, the use of niacin was discouraged in diabetic individuals because it was found to increase insulin resistance and degrade glycemic control, particularly at high doses (Sancetta 1951). However, emerging clinical evidence shows that niacin is both safe and effective for diabetics (Meyers 2004).
There is evidence that niacin reduces the risk of developing type 1 diabetes (Pocoit 1993; Pozzilli 1993). Niacinamide helps restore β-cells, or at least slow their destruction. Because niacin can disrupt blood sugar control in diabetics, individuals taking any form of niacin, including inositol hexaniacinate, must closely monitor blood sugar levels and discontinue treatment in the event of worsening of diabetic control. Inositol hexaniacinate has long been used in Europe to lower cholesterol levels and improve blood flow in individuals with intermittent claudication.
Vitamin C. Several preclinical studies evaluated vitamin C’s role during mild oxidative stress. The aqueous humor of the eye provides surrounding tissues with a source of vitamin C. Since animal studies have shown that glucose inhibits vitamin C uptake, this protective mechanism may be impaired in diabetes (Corti 2004). Supplementation with antioxidant vitamins C and E plays an important role in improving eye health (Peponis 2004). High vitamin C intake depresses glycation, which has important implications for slowing diabetes progression and aging (Krone 2004).
Vitamin C, through its relationship to sorbitol, also helps prevent ocular complications in diabetes. Sorbitol, a sugar-like substance that tends to accumulate in the cells of people with diabetes, tends to reduce the antioxidant capacity of the eye, with a number of possible complications. Vitamin C appears to help reduce sorbitol buildup (Will 1996).
Vitamin C also has a role in reducing the risk of other diabetic complications. In one clinical study, vitamin C significantly increased blood flow and decreased inflammation in patients with both diabetes and coronary artery disease (Antoniades 2004). Three studies suggest that vitamin C, along with a combination of vitamins and minerals (Farvid 2004), reduces blood pressure in people with diabetes (Mullan 2002) and increases blood vessel elasticity and blood flow (Mullan 2004).
Vitamin E. Vitamin E has been shown to significantly reduce the risk of developing type 2 diabetes (Montonen 2004). One double-blind trial found a reduction in the risk of cardiac autonomic neuropathy, or damage to the nerves that supply the heart, which is a complication of diabetes (Manzella 2001). Additional evidence documented benefits for diabetic peripheral neuropathy (Tutuncu 1998), blood sugar control (Kahler 1993; Paolisso 1993a,b; Paolisso 1994), and cataract prevention (Paolisso 1993a,b; Paolisso 1994; Seddon 1994). In addition, vitamin E enhances sensitivity to insulin in type 2 diabetics (Paolisso 1993a,b).
Before insulin, botanical medicines were used to treat diabetes. They are remarkably safe and effective. However, because many botanical medicines function similarly to insulin, people taking oral diabetes medications or insulin should use caution to avoid hypoglycemia. Botanical medicines should be integrated into a regimen of adequate exercise, healthy eating, nutritional supplements, and medical support.
Cinnamon. Cinnamon has been used for several thousand years in traditional Ayurvedic and Greco-European medical systems. Native to tropical southern India and Sri Lanka, the bark of this evergreen tree is used to manage conditions such as nausea, bloating, flatulence, and anorexia. It is also one of the world’s most common spices, used to flavor everything from oatmeal and apple cider to cappuccino. Recent research has revealed that regular use of cinnamon can also promote healthy glucose metabolism.
Astudy at the US Department of Agriculture’s Beltsville Human Nutrition Research Center isolated insulin-enhancing complexes in cinnamon that are involved in preventing or alleviating glucose intolerance and diabetes (Anderson 2004). Three water-soluble polyphenol polymers were found to have beneficial biological activity, increasing insulin-dependent glucose metabolism by roughly 20-fold in vitro (Anderson 2004). The nutrients displayed significant antioxidant activity as well, as did other phytochemicals found in cinnamon, such as epicatechin, phenol, and tannin. Moreover, scientists determined that these polyphenol polymers are able to upregulate the expression of genes involved in activating the cell membrane’s insulin receptors, thus increasing glucose uptake and lowering blood glucose levels (Imparl-Radosevich 1998).
The problem with long-term cinnamon use is the presence of highly reactive aldehyde compounds. These toxic fat-soluble compounds accumulate in the body over time. An aqueous extract of cinnamon has been identified and through a patented process, delivers cinnamon’s beneficial water-soluble nutrients while removing deleterious fat-soluble toxins.
In a recent double-blind, placebo-controlled trial (Stoecker 2010), a group of individuals (average age 61) with high blood sugar taking 500 mg daily of this form of cinnamon extract experienced an average decline of 12 mg/dL in fasting blood glucose after just two months. It also produced a significant decrease in postprandial glucose spikes (by an average of 32 mg/dL) after ingestion of 75 grams of carbohydrates. These findings support previous clinical data on similar aqueous cinnamon extracts, in which diabetic patients saw their fasting glucose drop an average of 10.3% after four months (Mang 2006).
Brown seaweed and bladderwrack. Another approach in managing glucose levels is to blunt the conversion of starches into their component sugars in the gastrointestinal tract. This can be accomplished safely and effectively by introducing natural enzyme inhibitors that halt carbohydrate metabolism in the gut. The most attractive targets are the sugar-producing alpha-amylase and alpha-glucosidase enzymes.
Extracts from a variety of seaweeds have inhibitory effects on these enzymes (Kim 2010; Apostolidis 2010; Kim 2008; Zhang 2007). Animal studies have revealed that inhibiting these enzymes lowers blood sugar levels (Heo 2009; Lamela 1989). In a recent double-blind, placebo-controlled clinical trial, a single dose of 500 mg daily of bladderwrack and seaweed significantly increased insulin sensitivity while inducing a 48.3% decline in postprandial glucose levels in healthy individuals (Lamarche 2010).
Irvingia gabonensis. Published studies show that extract of the African mango Irvingia gabonensis inhibits alpha-amylase-mediated conversion of carbohydrates into sugar (Oben 2008).
In 2006, researchers studied the effect of Irvingia in rats who were artificially induced to develop diabetes. A single oral dose of Irvingia lowered plasma glucose two hours after treatment (Ngondi 2006).
In 1990, researchers studied the effects of Irvingia on eleven human type 2 diabetics. Compared to baseline, there were significant reductions in blood triglyceride levels (16%), total cholesterol (30%), LDL (39 %), and glucose (38%), while HDL-cholesterol levels were increased by 29% after four-weeks of supplementation. These desirable biochemical effects were accompanied by improved clinical states (Adamson 1990).
Adiponectin is a hormone that plays a critical role in metabolic abnormalities associated with type 2 diabetes, obesity, and atherosclerosis (Berger 2002; Fasshauer 2004; Shand 2003; Yamauchi 2001; Kadowaki 2005; Kershaw 2004; Hotta 2001; Arita 1999; Ryo 2004; Yatagai 2003; Yamamoto 2004). Higher levels of adiponectin enhance insulin sensitivity; enhancing insulin sensitivity as we age is important to long-term metabolic health. Adipogenic transcriptional factors involved with adiponectin are also involved in the formation of new adipocytes, fat burning and endothelial function (Rosen 2000; Gustafson 2003; Oben 2008). Irvingia increases beneficial adiponectin levels and inhibits adipocyte differentiation mediated through the suppression of adipogenic transcription factors (Oben 2008).
White kidney bean. Extracts from the common white kidney bean, Phaseolus vulgaris, are powerful blockers of the enzyme alpha-amylase (Mosca 2008; Obiro 2008). White bean extract shows enormous potential for preventing the blood sugar and insulin spikes associated with many chronic health disorders (Preuss 2007).
Amylase inhibition with white bean extract has proven particularly effective in reducing glycemia (sugar load in the blood) in studies on diabetic animals. Supplementation in diabetic rats not only substantially lowered mean blood sugar levels, but it also reduced the animals’ total food and water intake (water intake is increased in untreated diabetes because of the amount lost in sugar-laden urine) (Tormo 2006).
White bean extract has yielded equally compelling results in human studies. It has been shown to diminish the effects of high-glycemic index foods (like white bread) that are notorious for producing sharp, potentially dangerous postprandial blood sugar spikes, helping to alleviate metabolic burden throughout the body (Udani 2009).
In one notable study, postprandial blood sugar levels were measured in a group of healthy subjects after consuming 50 grams of carbohydrate in the form of wheat, rice, and other high-carbohydrate plant foods (Dilawari 1981). Phaseolus vulgaris inhibited the average post-ingestion spike in blood sugar by 67%.
Green coffee extract. Coffee contains some well-studied phytochemicals such as chlorogenic acid, caffeic acid, ferulic acid, and quinic acid (Charles-Bernard 2005). Some of coffee’s most impressive effects can be seen in blood glucose management. Chlorogenic acid and caffeic acid are the two primary nutrients in coffee that benefit individuals with high blood sugar. Glucose-6-phosphatase is an enzyme crucial to the regulation of blood sugar. Since glucose generation from glycogen stored in the liver is often overactive in people with high blood sugar (Basu 2005), reducing the activity of the glucose-6-phosphatase enzyme leads to reduced blood sugar levels, with consequent clinical improvements.
Chlorogenic acid has been shown to inhibit the glucose-6-phosphatase enzyme in a dose-dependent manner, resulting in reduced glucose production (Hemmerle 1997). In a trial at the Moscow Modern Medical Center, 75 healthy volunteers were given either 90 mg chlorogenic acid daily or a placebo. Blood glucose levels of the chlorogenic acid group were 15 to 20 percent lower than those of the placebo group (Abidoff 1999). Chlorogenic acid also has an antagonistic effect on glucose transport, decreasing the intestinal absorption rate of glucose (Johnston 2003), which may help reduce blood insulin levels.
In another trial, researchers gave different dosages of green coffee bean extract, standardized for chlorogenic acid, to 56 people. Thirty-five minutes later, they gave the participants 100 grams of glucose in an oral glucose challenge test. Blood sugar levels dropped by an increasingly greater amount as the test dosage of green coffee bean extract was raised (from 200 mg to 400 mg). At the 400 mg dose, there was a full 24% decrease in blood sugar—just 30 minutes after glucose ingestion (Nagendran 2011).
Green coffee bean extract found in unroasted coffee beans, once purified and standardized, produces high levels of chlorogenic acid and other beneficial polyphenols that can suppress excess blood glucose levels. Roasting destroys much of the coffee bean’s beneficial content.
Garlic. Allium is the active component in garlic and onions. Allium compounds are sulfur-donating compounds that help reconstitute glutathione, a major internal antioxidant. This mechanism is probably responsible for allium’s positive effects. Allium has a number of positive effects that may help reduce the risk of diabetic complications, including the following:
Green tea. The compounds in these plants, including epicatechin, catechin, gallocatechin, and epigallocatechin, are powerful antioxidants, particularly against pancreas and liver toxins (Okuda 1983). Animal studies have shown that epigallocatechins, in particular, may have a role in preventing diabetes (Crespy 2004). In studies with rats, epigallocatechins prevented cytokine-induced β-cell destruction by downregulating inducible nitric oxide synthase, which is a pro-oxidant (Kim 2004; Song 2003). This process could help slow the progression of type 1 diabetes. In vitro studies have also shown that green tea suppresses diet-induced obesity (Murase 2002), a key risk factor in developing diabetes and metabolic syndrome (Hung 2005).
Vitamin D. Vitamin D has far-reaching implications that extend beyond promoting bone health. Over the past 40 years, research has shed light on the intersecting pathways of vitamin D and many other aspects of health.
Evidence from animal experiments and human observational studies suggests that vitamin D may help prevent type I diabetes, perhaps by acting as an immune system modulator (Zittermann 2007). Researchers demonstrated that the pancreatic β-cells of mice contain receptors for 1,25-dihydroxyvitamin D. When they administered this active form of vitamin D to mice early in life, the animals demonstrated a reduced incidence of type I diabetes. However, diabetes incidence was not affected when 1,25-dihydroxyvitamin D was administered to mice later in life. Vitamin D appears to limit the expression of certain cytokines, which may prevent the autoimmune attack on pancreatic cells that can lead to diabetes (Targher 2006).
Human studies likewise suggest that vitamin D may have a protective effect against type I diabetes. In a large-scale investigation, more than 12,000 pregnant women in Finland enrolled in a trial studying the relationship between vitamin D intake and type I diabetes in infants. After one year, children who supplemented with the suggested study dose of vitamin D (2000 IU daily) had a much lower risk of type I diabetes than children who did not supplement (Levin 2005).
Vitamin D supplementation may reduce susceptibility to type II diabetes by slowing the loss of insulin sensitivity in people who show early signs of the disease. Researchers studied 314 adults without diabetes and gave them either 700 IU of vitamin D and 500 mg of calcium daily or a placebo for three years (Pittas 2007). Among subjects who had impaired (slightly elevated) fasting glucose levels at the study’s onset, those taking the active supplement had a smaller rise in glucose levels over three years than did the controls, as well as a smaller increase in insulin resistance. The researchers concluded that for older adults with impaired glucose levels, supplementing with vitamin D and calcium may help avert metabolic syndrome and type II diabetes.
Ginkgo biloba. Animal studies demonstrate that ginkgo improves glucose metabolism in muscle fibers and prevents atrophy (Punkt 1999). Animal studies also show that ginkgo biloba extracts significantly inhibit post-meal sugar levels and act as anti-hyperglycemic agents (Tanaka 2004).
Ginkgo biloba extract has been shown to prevent diabetic retinopathy in diabetic rats, suggesting a protective effect in human diabetics (Doly 1988). In a preliminary clinical trial (Huang 2004), type 2 diabetics were given ginkgo extract orally for three months, which significantly reduced free radical levels, decreased fibrinogen levels, and improved blood viscosity. Ginkgo extracts also improved retinal capillary blood flow rate in type 2 diabetic patients with retinopathy.
Ginkgo has also been observed to lower blood glucose levels. It was studied in type 2 diabetics at a dose of 120 mg for three months. Ginkgo supplementation produced an increase in liver metabolism of insulin and oral hypoglycemic medications, which corresponded to a reduction in plasma glucose levels (Kudolo 2001). Type 2 diabetics with pancreatic exhaustion received the most benefit. Ginkgo does not appear to increase beta cell production; rather it enhances liver uptake of existing insulin, thereby reducing high insulin levels.
Blueberries. Native to North America, blueberries have long been used in food preparation and for therapeutic purposes (Prett 2005). Many of the health benefits attributed to blueberries have been linked to their potent antioxidant properties. Scientists attribute these powerful antioxidant properties to polyphenols in blueberries known as anthocyanins
In published studies, blueberries block carbohydrate metabolism in the intestine by up to 90% compared with the prescription drug acarbose (Johnson 2011; Melzig 2007).
Additionally, blueberries have been shown to lower baseline blood sugar levels in those diagnosed with type 2 diabetes by 37% (Vuong 2009; Abidov 2006; Takikawa 2010).
In a double-blind, placebo-controlled study, 32 obese, insulin-resistant (pre-diabetic) adult men and women drank smoothies made with freeze-dried blueberry powder for six weeks. A placebo control group consumed smoothies without blueberry extracts (Stull 2010). Fasting blood samples were obtained with a clamp technique considered state-of-the-art for precise determination of insulin sensitivity. With no changes in body weight or composition compared to controls, the blueberry group showed a statistically significant and much greater improvement in insulin sensitivity (22.2% plus or minus 5.8%) versus the placebo arm (4.9% plus or minus 4.5%).
Vaccinium myrtillus (bilberry). Studies of diabetic rats show that bilberry decreases vascular permeability (Cohen-Boulakia 2000). Studies of diabetic mice receiving an herbal extract containing bilberry demonstrated significantly decreased blood glucose levels (Petlevski 2001; Petlevski 2003).
A double-blind, placebo-controlled trial of bilberry extract in 14 people with diabetic retinopathy or hypertensive retinopathy (damage to the retina caused by diabetes or hypertension, respectively) found significant improvements in the treated group (Bone 1997). Other open clinical trials in humans also showed benefits. A preliminary study of 31 people with retinopathy documented that bilberry reduced vascular permeability and reduced hemorrhage (Scharrer 1981).