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Soya: the health protector - The health effects of SoyaThyroid FunctionAnother area of controversy is the possible role soya may have in thyroid function. The thyroid is a small endocrine gland found in the front of the neck. It produces thyroid hormones and secretes them into the bloodstream. These hormones regulate the body’s metabolism, heart rate, body temperature and help control how fast the body uses energy from food. Every cell in the body depends on thyroid hormones for regulation of their metabolism. Hypothyroidism, or an underactive thyroid, is when insufficient thyroid hormones are produced. When it occurs from birth it is called congenital hypothyroidism. Iodine is a trace element found in seawater, rocks and some types of soil. It is essential for the production of thyroid hormone so low levels of iodine can result in low levels of hormone. This can cause the pituitary gland at the base of the skull to produce more thyroid stimulating hormone (TSH) in an effort to boost thyroid hormone production. This makes the thyroid gland work harder, causing it to enlarge and form what is called a goitre. If the lack of iodine is very severe, hypothyroidism can result In the UK, this is virtually unheard of as even very poor diets tend to contain enough iodine. In the few cases of iodine-deficiency related goitre that have been reported, supplementation with iodine (kelp) has been shown to shrink the goitre (Park et al., 2005). 
Natural substances called goitrogens, found in soya, broccoli, kale, cabbage, turnips, millet, peanuts and pine nuts, can interfere with the uptake of iodine and lead to a goitre. However, this is not a problem if the diet provides enough iodine. A small number of studies have suggested that soya isoflavones may also affect thyroid function by lowering thyroid hormone concentrations. In a cautionary statement, the COT advises health care professionals to be aware of possible links between isoflavones in soya formulas and thyroid function, particularly in cases of congenital hypothyroidism (COT, 2003). However, a review of 14 different studies looking at the effects of soya on thyroid function found little evidence that it had an adverse effect in people whose thyroid function is normal and whose diet contains sufficient iodine (Messina and Redmond, 2006). The authors suggest that soya foods may interfere with absorption of medication containing synthetic thyroid hormone but that hypothyroid adults need not totally avoid soya foods. There is also a theoretical concern that in individuals with compromised thyroid function and/or whose iodine intake is marginal, soya foods may increase the risk of developing hypothyroidism. The general consensus is that all people, whether soya consumers or not, should ensure their intake of iodine is adequate. The Department of Health recommends that toddlers aged one to three should get 70 micrograms of iodine per day and adults 140 micrograms (Department of Health, 1991). Good sources include sea vegetables with a consistent iodine content, such as kelp (kombu). Only a small amount is required as too much iodine can be harmful. The UK Food Standards Agency considers that 500 micrograms or less a day is unlikely to cause any harm (FSA, 2010a). You can use small amounts of powdered or crumbled sea vegetables added to soups, stews, salads, pasta dishes or used as a condiment, to ensure a sufficient iodine intake. Alternatively, adults can supplement their diet with kelp tablets but these are not suitable for children. Other sea vegetables such as nori (used in sushi), wakame and arame are relatively low in iodine and can be eaten in moderation without concern about excess iodine. Refer to the packaging for exact figures and recommendations. Iodine is also found in cereals and grains, such as whole wheat and rye, but levels vary depending on the amount of iodine in the soil where the plants are grown. For more information, see the VVF’s factsheet, Talking Thyroid Facts.
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The Soya Story - ContentsResources:
Myth-Busting Soya and the Environment FAQs Soya research |
The Soya Story
The Safety of Soya 
Soya-Based Infant Formula 
The Soya Saga  |
Vegetarian & Vegan Foundation Top Suite, 8 York Court, Wilder Street, Bristol, BS2 8QH, UK T: 0117 970 5190 W: www.vegetarian.org.uk E: info@vegetarian.org.uk |
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