Diabetes and serum carotenoids

Nutrition Research Newsletter, Oct, 2005

Carotenoids are a wide range of compounds derived solely from plants. The major ones include r-carotene, a-carotene, a-cryptoxanthin, lutein/zeaxanthin, and lycopene. Considerable epidemiologic evidence exists that some carotenoids are potent antioxidants and may play a protective role against the development of chronic disease such as atherosclerosis, stroke, certain cancers and inflammatory diseases. Although obesity and physical inactivity are known to be major risk factors for type 2 diabetes, evidence suggests that oxidative stress may also contribute to the pathophysiology of type 2 diabetes. In addition, serum or dietary vitamin A, E and C levels have been hypothesized to be lower in persons with IGT or with type 2 diabetes. Therefore, a recent study investigated the relationship between the major serum carotenoids and type 2 diabetes status in a cross-sectional population-based study in Queensland, Australia.

Adults aged older than 25 years from six randomly selected cities and towns in Queensland, Australia were included in the study: Fasting plasma glucose, an oral-glucose tolerance test and measurement of the serum concentrations of five carotenoid compounds were measured between October 2000 and December 2000. Demographic and lifestyle variables were collected by using standardized questionnaires.

Mean 2-hour postload plasma glucose and fasting insulin concentrations decreased significantly with increasing quintiles of the five serum carotenoids--a-carotene, a-carotene, a-cryptoxanthin, lutein/zeaxanthin, and lycopene. Fasting glucose concentrations also decreased significantly with increasing quintiles of a-carotene and a-carotene. Geometric mean concentrations for all serum carotenoids decreased with declining glucose tolerance status. a-carotene had the greatest decrease, to geometric means of 0.59, 0.50, and 0.42 gmol/L in persons with normal glucose tolerance, impaired glucose metabolism, and type 2 diabetes, respectively.

The results show that serum carotenoids are inversely associated with type 2 diabetes and impaired glucose metabolism. Randomized trials of diets high in carotenoids-rich vegetables and fruits are needed to confirm these results and those from other observational studies. Such evidence would have very important implications for the prevention of diabetes.

Terry Coyne, Torukiri I. Ibiebele, Peter D. Baade, et al. Diabetes Mellitus and Serum Carotenoids: Findings of a Population-Based Study in Queensland, Australia. AJCN; 82:685-693 (September 2005) [Reprints not available. Correspondence: T. Coyne, School of Population Health, The University of Queensland, Public Health Building, Herston 4029, Queensland, Australia. E-mail:t.coyne@sph.uq.edu.au].