Diabetes & Nutrition Part III: Complementary Nutrients

Complementary Nutritional Support

Part I of the Diabetes and Nutrition series (see December 2008 issue) discussed the importance of diet and calories in helping to prevent type 2 diabetes, as well as the benefits of eating a low glycemic diet for better blood sugar control. Part II covered essential vitamins and minerals that can be compromised in diabetics - or those at risk for the disease - due to poor intake, faster excretion, or greater need (see January 2009 issue). The series concludes with a look at three complementary nutrients: alpha lipoic acid, quercetin and polyphenols. Evidence suggests this trio can play an important role in a diabetic's nutritional support team.

Protective Properties of Alpha Lipoic Acid

As mentioned in Part II, people with diabetes have higher levels of oxidative stress which can contribute to long-term complications. Antioxidants help counter oxidative stress, and alpha lipoic acid is a unique antioxidant. Made in the body and found in foods such as spinach, broccoli and potatoes, alpha lipoic acid can scavenge free radicals, and also appears to bolster levels of the antioxidant enzyme glutathione (1).

Because alpha lipoic appears to be particularly helpful in protecting nerve cells, it is being studied in neurodegenerative disorders such as Alzheimer's and Parkinson's disease. A number of trials (2) have also reported that high dose alpha lipoic eases symptoms such as pain and numbness in patients with diabetic neuropathy, a complication of diabetes.

Research in models of diabetic retinopathy suggests that this antioxidant could have a role in protecting the eye's retina as well. In one study (3), giving alpha lipoic early to diabetic mice reduced markers of oxidative stress, shored up glutathione levels and helped normalize electrical signals in the retina.

Multi-Faceted Quercetin

Quercetin is a flavonoid (part of the polyphenol family of compounds) and is present in a variety of fruits and vegetables such as onions, apples, citrus fruit, grapes and broccoli. Consuming plenty of flavonoids, especially quercetin, has been associated with lower incidence of heart disease and stroke. Quercetin's apparent ability to counter oxidative stress makes it an attractive candidate for the diabetic's nutrition arsenal.

In one clinical trial (4), diabetics had less oxidative damage to DNA within white blood cells when eating a high vs. a low quercetin diet. If results from laboratory studies are shown to hold true in people, quercetin may have a role in visual health as well. Quercetin has been shown to protect lab-grown human retinal pigment epithelial and cortical cells during oxidative stress (5).

Procyanidins Support Healthy Vessels, Vision

Procyanidins, plentiful in grapes and cocoa, have both antioxidant and anti-inflammatory actions. Importantly for diabetics, procyanidins extracted from pine (Pycnogenol®) may also help keep blood vessel walls strong and enhance compounds that help arteries dilate. This source of procyanidins has been tested in more than 1200 people with retinopathy and diabetic retinopathy in various trials, with reported results generally supporting benefit (6).

In a recent double-blind study (7) of diabetics with hypertension taking ACE inhibitor medication, 58% were able to achieve better blood pressure control at lower doses of medication after 3 months of Pycnogenol supplementation. Significant effects on other cardiovascular disease risk factors were also seen in the pine procyanidin group vs. placebo.

References

1. Peterson, et al. Critical Review: Is alpha-lipoic acid a scavenger of reactive oxygen species in vivo? Evidence for its initiation of stress signaling pathways that promote endogenous antioxidant capacity. Life 60: 362-67, 2008.
   
2. Singh U, et al. Alpha-lipoic acid supplementation and diabetes. Nutr Rev 66:646-57, 2008.
   
3. Johnsen-Soriano S, et al. Early lipoic acid intake protects retina of diabetic mice. Free Rad Res 4:613-17, 2008.
   
4. Lean MEJ, et al. Dietary flavonols protect diabetic human lymphocytes against oxidative damage to DNA. Diabetes 48:176-181, 1999.
   
5. Hanneken A, et al. Flavonoids protect human retinal pigment epithelial cells from oxidative stress-induced death. Invest Ophthalmol Vis Sci 47:3164-77, 2006.
   
6. Schönlau F, et al. Pycnogenol for diabetic retinopathy: A review. Inter Ophthalmol 24:161-71, 2002.
   
7. Zibadi S, et al. Reduction of cardiovascular risk factors in subjects with type 2 diabetes by Pycnogenol supplementation. Nutr Res 28:315-20, 2008.