Food plants species in the Cruciferae (Brassicaceae) family contain substances called glucosinolates, which probably play a role in the plant's defenses against predators and fungal attack. When eaten by animals or humans, glucosinolates can inhibit thyroid gland functioning, causing enlargement and atrophy of the thyroid, or goiter.
Brassica species containing goitrogens include cabbage, broccoli, cauliflower, rutabaga, kohlrabi, and the oilseeds, rapeseed and canola. The enzymes required for production of goitrogens in the plant are destroyed by cooking. Goitrogens are also lost through leaching into cooking water.
Effects in Animals
Feeding rapeseed meal with high glucosinolate levels to animals and poultry induces enlarged thyroids, reduced circulating thyroid hormones, liver, kidney, and adrenal abnormalities, and poor growth and reproductive performance.6
Effects in Humans
One study showed no ill effects when volunteers ingested 40 mg goitrin/day in Brussels sprouts over a 4-week period. Another study showed inhibition of iodine uptake after administration of 50-200 mg of goitrin. Studies in Great Britain estimated an average intake of 76 mg glucosinolate per person per day, with a range of up to 200 mg per day. 2 Whether or how much the consumption of Brassica vegetables contributes to ill health in humans is unknown. The cause of endemic goiter in certain geographic regions may be the result of the interaction between iodine deficiency and certain food components, such as glucosinolates.1
Many nutritional studies have shown that dietary fruits and vegetables, including those in the Brassica group, have a protective effect against certain cancers. In animal studies, glucosinolates and their breakdown products have inhibited tumor formation, although this anti-carcinogenic effect depends on the study design, the type of cancer being studied, whether other dietary components are present, and the timing of the administration of the glucosinolate compound.6
In summary, glucosinolates are known to be goitrogenic in animals, but their role in inducing goiter in humans is less clear. They can be anti-carcinogenic and cancer-promoting, depending on the species and circumstances of administration.6 In general, dietary vegetables, including Brassica vegetables, are beneficial in cancer prevention.
Back to List of Endogenous Plant Toxins
Prepared Summer 1997 by Bernadene Magnuson, Ph.D.
University of Idaho, Dept. of Food Science and Toxicology - EXTOXNET FAQ Team.