Long-term use of high doses of soy dietary supplements is POSSIBLY UNSAFE. There is concern that taking high doses might cause abnormal tissue growth in the uterus.
Cystic fibrosis: Soymilk can interfere with the way children with cystic fibrosis process protein. Don’t give these children soy products.
Breast cancer: The effects of soy in people with breast cancer are unclear. Some research finds that soy might “feed” certain breast cancers because it can act like estrogen. Other studies have found that soy seems to protect against breast cancer. The difference in effects might have something to do with the amount taken. Because there isn’t enough reliable information about the effects of soy in women with breast cancer, a history of breast cancer, or a family history of breast cancer, it’s best to avoid using soy until more is known.
Endometrial cancer: Long-term use of concentrated soy isoflavone tablets might increase the occurrence of precancerous changes in the tissue lining the uterus. Don’t take concentrated soy isoflavone supplements if you have endometrial cancer.
Kidney disease: There is some concern that soy products might increase the risk of kidney stones because they contain large amounts of a group of chemicals called oxalates. Oxalates are the main ingredient in kidney stones. Another concern is that people with serious kidney disease aren’t able to process some of the chemicals in soy. This could lead to dangerously high levels of these chemicals. If you have kidney disease or a history of kidney stones, avoid taking large amounts of soy.
Urinary bladder cancer: Soy products might increase the chance of getting bladder cancer. Avoid soy foods if you have bladder cancer or a high risk of getting it (family history of bladder cancer).
Under-active thyroid (hypothyroidism): There is a concern that taking soy might make this condition worse.
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