News - Alpha-lipoic acid: a promising antioxidant for type-2 diabetics
A new study, published in the Saudi Medical Journal, has discovered that alpha-lipoic acidcan help to improve blood sugar control and insulin sensitivity, and reduce levels of oxidative stress in patients with type-2 diabetes – all key issues for addressing diabetic complications and cardiovascular disease.
Alpha-lipoic acid (ALA, also known as lipoic acid or thioctic acid) is a sulphur-containing fatty acid. It plays a crucial role in the energy-producing structures within cells called the mitochondria, which convert the energy from food into a form that cells can use. ALA also has unique and powerful antioxidant properties.
Antioxidants are substances that help to neutralise and protect the body against highly reactive and harmful chemicals known as free radicals, which have the potential to damage DNA, proteins and lipids (fats) in cell membranes. Free radicals have been implicated in ageing, cataracts, heart disease and cancer, among other ills.
Antioxidants are either water-soluble or fat-soluble substances and therefore work in water or fat. For example, vitamin C is a water-soluble antioxidant that protects the watery areas, such as blood and inside cells, against free radicals; and vitamin E is a fat-soluble antioxidant that protects the cell membrane, which is made up mostly of fats, from damage by free radicals. In contrast, ALA is both water-soluble and fat-soluble, which is unique among antioxidants. In this manner, ALA serves to protect both the water and fat portions of the cell. This gives ALA an unusually broad spectrum of antioxidant action.
Regeneration of other antioxidants
When antioxidants neutralise a free radical, they become oxidised (inactivated), and are no longer able to neutralise additional free radicals. ALA has the ability to regenerate other antioxidants – including vitamin C, vitamin E, glutathione and coenzyme Q10 – from their inactive forms back to their free-radical-fighting forms. It can therefore extend the lifespan of these important and powerful antioxidants.
Increased levels of glutathione
ALA has also been shown to increase the production and levels of glutathione. Glutathione is one of the principal antioxidant free radical scavengers in living cells, and also plays an important role in protecting cells against xenobiotics (highly toxic man-made chemicals), radiation, and heavy metals. In addition, glutathione is involved in protein and DNA synthesis, cell proliferation, the maintenance of a healthy cell membrane and regulating the movement of important signals from outside to the inside of the cell. Glutathione deficiency contributes to oxidative stress. Oxidative stress exists when free radical production exceeds our available antioxidant defences, and has been implicated in the pathogenesis of many diseases, including Alzheimer’s disease, Parkinson’s disease, cancer, heart attack, stroke and diabetes.
Diabetes and ALA
Diabetes is a major health problem worldwide. It is a disease marked by high levels of sugar (glucose) in the blood, which reflects the body’s inability to regulate blood sugar levels. Type-2 diabetes is the most common form of diabetes, accounting for more than 90% of cases. It occurs when the body’s muscle and liver cells become resistant to the actions of insulin (the hormone that carries glucose into the body’s cells to be used for energy), which causes blood sugar levels to rise.
Chronic elevated blood sugar levels can result in an increase in free radical production, resulting in oxidative stress. A review of scientific studies suggest that oxidative stress is connected to the development of insulin resistance, and the subsequent development of type-2 diabetes. There is also considerable evidence to indicate that many of the complications associated with diabetes, including neuropathy (a nerve disorder) and cataract formation, appear to be mediated by the excessive production of free radicals.
Interventions that reduce oxidative stress may therefore help to support the normal actions of insulin in insulin-resistant subjects. This has prompted scientific investigations in the use of antioxidants, as an adjuvant to standard diabetic therapy.
Studies have shown ALA to have beneficial effects in diabetes. ALA has been found to increase glucose uptake into muscle and fat cells. ALA has also been shown to improve the actions of insulin in type-2 diabetic subjects. This was confirmed by a very recent study at the Nutrition Department, School of Health and Nutrition, Shiraz, Iran, that is affiliated to Shiraz University of Medical Sciences.
Effects of ALA on blood sugar, insulin resistance and oxidative stress
The aim of this study was to examine the effects of ALA supplementation, over a period of two months, on fasting blood sugar levels (tested before breakfast, following at least eight hours since the previous night’s meal), postprandial (after-meal) blood sugar levels(measured two hours after a meal), insulin resistance and glutathione peroxidase levels in type-2 diabetic patients.
The control of blood sugar levels is an important goal of diabetes therapy, and can be monitored by measuring fasting and postprandial blood sugar levels. Glutathione peroxidase is a key naturally-occurring antioxidant enzyme that requires glutathione to function. It plays a central role in protecting cells from oxidative stress.
Fifty-seven patients with type-2 diabetes were randomly divided into two groups to receive either ALA or a placebo (dummy pill) for a period of eight weeks. Fasting blood sugar levels were measured following an overnight fast and after-meal blood sugar levels were measured two hours after breakfast. Blood levels of insulin were also measured. Insulin resistance was calculated from the fasting blood insulin and glucose levels.
The results of this study showed a significant decrease in fasting blood sugar levels, after-meal blood sugar levels, and the calculated insulin resistance in the group taking ALA. The activity of the enzyme glutathione peroxidase significantly decreased in the ALA group compared to the placebo group.
The overall results of this study suggest that supplementation with ALA improves blood sugar control and insulin sensitivity in type-2 diabetes. Diabetes has been associated with an increase in oxidative stress. Previous studies have shown that in poorly controlled type-2 diabetes, glutathione peroxidase activity is significantly higher than in sex- and age-matched healthy subjects. This increased glutathione peroxidase activity may be part of an ‘antioxidant adaptive response’ for combating damage caused by oxidative stress. The significant decrease in glutathione peroxidase activity following supplementation with ALA suggests that ALA behaves as an effective antioxidant, reducing oxidative stress and therefore the need for an antioxidant adaptive response.
The researchers commented: “This study supports the use of ALA as an antioxidant in the care of diabetic patients.”
Ansar H, Mazloom Z, Kazemi F et al. Saudi Med J. 2011;32:584-8.