Dietary Estrogens of Plant and Fungal Origin: Occurrence and Exposure

Abstract

Phytoestrogens and mycoestrogens are naturally occurring dietary compounds that strongly resemble the structrure of the mammalian steroidal estrogens. Lignans, isoflavones, and coumestans are the three major classes of phytoestrogens to which humans and animals are exposed. Animals may be exposed to high levels of phytoestrogens while grazing in pastures or consuming feed rich in clover of alfalfa. Domestic livestock may be exposed to mycoestrogens, primarily zearalenone, by consuming feed that is contaminated with Fusarium spp. toxins. Livestock consuming feed is exposed to 907--1195 mg of isoflavones/kg of feed. In clover pastures, livestock is exposed to isoflavones at a level of 0.05--4.8% (dry weight). Mycoestrogen exposure varies according to the level of contamination of feed. The zearalenone content of animal feed is estimated to be within 14--215 ng/g depending on the geographical region and type of grain or cereal consumed. With respect to human exposure, lignans and isoflavones are most commonly found in foods containing flaxseed or soybeans, respectively. Since the extent of phytoestrogen exposure is dependent on dietary composition, vegetarians or infants receiving soy-based infant formulas have a significantly higher level of exposure to phytoestrogens. Humans may be exposed to trace or low levels of mycoestrogens via consumption of cereal or cereal products that are mildly contaminated with zearalenone. Dietary intakes of zearalenone are estimated to be 100--500 ng/kg body weight per day. Both animal and human studies have demonstrated that exposure to phytoestrogens and mycoestrogens can result in estrogen-like or antiestrogen-like effects depending on the timing of exposure in the life-cycle, the duration of exposure, and the dose administered. Accordingly, these compounds can have adverse effects or health benefits. Alterations in reproductive indices that lead to reduced fertility rates have been reported in animals grazing in pastures containing phytoestrogens or consuming feed ontaminated with mycoestrogens. Impairments in sexual behavior and alterations in measures of masculinity as well as modifications in carcass composition have been reported in animals implanted with a synthetic analogue of zearalenone. In humans, the progression of diseases in which estrogen may play a role, such as cancer, cardiovascular disease, and osteoporosis, may be attenuated with phytoestrogen exposure. Exposure to phytoestrogens during critical developmental periods may reduce the risk of disease development in later life.