Association of serum carotenoids and tocopherols with gamma-glutamyltransferase: the Cardiovascular Risk Development in Young Adults (CARDIA) Study.

BACKGROUND Our previous studies suggest that serum gamma-glutamyltransferase (GGT) activity may be related to oxidative stress, supporting findings of experimental studies. To further examine the role of GGT in relation to oxidative stress, we investigated the association between serum carotenoids and tocopherols, which have antioxidant properties, and serum GGT. METHODS Study participants were 3128 black and white men and women 17-35 years of age in 1985-1986. Serum carotenoids and tocopherols were measured at years 0 and 7, and serum GGT was measured at years 0 and 10. RESULTS Circulating concentrations of alpha-carotene, beta-carotene, and beta-cryptoxanthin inversely predicted the serum GGT concentration measured 10 years later in a dose-response manner (P for trend <0.01). Year 0 zeaxanthin/lutein was weakly inversely associated with year 10 GGT (P for trend = 0.08), and year 0 lycopene was unrelated to year 10 GGT. Adjusted geometric means of serum GGT at year 10 according to quintile of the sum of four carotenoids at year 0 (alpha-carotene, beta-carotene, beta-cryptoxanthin, and zeaxanthin/lutein) were 19.9, 19.4, 18.9, 17.8, and 17.3 U/L (P for trend <0.01). Year 0 alpha-tocopherol was also a significant inverse predictor of year 10 serum GGT concentration (P for trend = 0.03), whereas gamma-tocopherol showed an inconsistent or possibly U-shaped association. However, year 0 serum GGT did not predict serum antioxidants measured 7 years later. CONCLUSION Our present findings support the contention that serum GGT concentration is a marker related with oxidative stress.