Insulin resistance is characterised by an increase in the fasting plasma levels of insulin and glucose, and this is caused by a reduction in the efficiency of the insulin signalling system in the peripheral tissues. The development of insulin resistance is now associated with a number of diseases including cardiovascular disease, type 2 diabetes, obesity and Alzheimer’s disease. The cause of insulin resistance is not fully understood, and a number of theories have been put forward to explain its aetiology. Current evidence suggests that low quality diets, in combination with a sedentary lifestyle, are the main causative factors in the development of the insulin resistant state in Western populations. Just how these factors cause insulin resistance is not known, but one suggestion is that nutrient overload causes increased free radical generation as a result of increased flux through the oxidation pathways, and this oxidative stress causes cellular changes including a desensitisation of the insulin receptor.
If the oxidative stress caused by nutrient overload is responsible for the development of insulin resistance, it would be expected that associations might be found between the antioxidant status of an individual and their degree of insulin resistance. In addition, it might be expected that there would be an association between the oxidative stress and the degree of insulin resistance. A number of studies have investigated the associations between antioxidants or lipid peroxides in the plasma and the degree of insulin resistance in human subjects. For example, in one study1, researchers observed an inverse association between plasma levels of α-carotene, β-carotene, lutein, α-tocopherol and δ-tocopherol with insulin resistance in non-diabetic individuals. Associations between arterial blood pressure and plasma hydroperoxide concentrations with insulin resistance were also reported. These results support the contention that insulin resistance is accompanied by oxidative stress and the depletion of plasma antioxidant defences.
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