Plasma insulin-like growth factor I levels in rats are reduced by dietary supplementation of flaxseed or its lignan secoisolariciresinol diglycoside.

Key Findings

This study investigated the link between lignans and insulin-like growth factor I (IGF-I) which is important for the development of terminal end buds in the mammary gland. Flaxseed and SDG reduced plasma IGF-I which may contribute to inhibitory effects on carcinogenesis. Dietary supplementation with 5% flaxseed or 1.5 mg SDG/day for 4 weeks reduced plasma levels of IGF-I in rats treated with or without MNU. Urinary lignan excretion, a marker of lignan bioavailability, was inversely related to plasma IGF-I concentrations, particularly when dietary lignan treatment occurred before 50 days of age. The reduction in plasma IGF-I with flaxseed and SDG treatment appeared to be stronger in experiment 1 (before 50 days of age).

ABSTRACT

Flaxseed and its lignan secoisolariciresinol diglycoside (SDG) inhibit mammary tumor development in rats. Increased plasma insulin-like growth factor I (IGF-I) concentrations are associated with increased breast cancer risk. Therefore, the effect of flaxseed (5%) or SDG (1.5 mg/day) supplementation on plasma IGF-I levels was examined in rats treated with or without N-methyl-N-nitrosourea (MNU). In MNU-free rats, flaxseed and SDG reduced plasma IGF-I levels, which were inversely related to urinary lignan excretion. Only flaxseed significantly reduced plasma IGF-I concentrations in MNU-treated rats. The anticancer effect of flaxseed and SDG may be related, in part, to reductions in plasma IGF-I.