Soy : Safety, Part 2

by MedlinePlus

(Page 4 of 4)

The use of soy is often discouraged in patients with hormone-sensitive malignancies such as breast, ovarian, or uterine cancer, due to concerns about possible estrogen-like effects (which theoretically may stimulate tumor growth). Other hormone-sensitive conditions such as endometriosis may also theoretically be worsened. In laboratory studies, it is not clear if isoflavones stimulate or block the effects of estrogen, or both (acting as a "receptor agonist/antagonist"). Until additional research is available, patients with these conditions should be cautious and speak with a qualified healthcare practitioner before starting use.

It is not known if soy or soy isoflavones share the same side effects as estrogens, such as increased risk of blood clots. Preliminary studies suggest that soy isoflavones, unlike estrogens, do not cause the lining of the uterus (endometrium) to build up.

There has been a case report of a vitamin D deficiency rickets in an infant nursed with soybean milk (not specifically designed for infants). Patients should consult a qualified healthcare practitioner for current breastfeeding recommendations, use formulas with adequate nutritional value.

Pregnancy and Breastfeeding

Soy as a part of the regular diet is traditionally considered to be safe during pregnancy and breastfeeding, although scientific research is limited in these areas. The effects of high doses of soy or soy isoflavones in humans are not clear, and therefore are not recommended.

Recent study demonstrates that isoflavones, which may have estrogen-like properties, are transferred through breast milk from mothers to infants. High doses of isoflavones given to pregnant rats have resulted in tumors in female offspring, although this has not been tested in humans.

In one human study, male infants born to women who ingested soymilk or soy products during pregnancy experienced more frequent hypospadias (a birth defect in which the urethral meatus, the opening from which urine passes, is abnormally positioned on the underside of the penis). However, other human and animal studies have examined males or females fed soy formula as infants, and have not found abnormalities in infant growth, head circumference, height, weight, occurrence of puberty, menstruation, or reproductive ability.

Research in children during the first year of life has found that the substitution of soy formula for cow's milk may be associated with significantly lower bone mineral density. Parents considering the use of soy formula should speak with a qualified healthcare practitioner to make sure the appropriate vitamins and minerals are provided in the formula.

Interactions

Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy.

Interactions with Drugs

Estrogen: Soy contains "phytoestrogens" (plant-based compounds with weak estrogen-like properties) such as isoflavones. In laboratory studies, it is not clear if isoflavones stimulate or block the effects of estrogen, or both (acting as a "receptor agonist/antagonist"). It is not known if taking soy or soy isoflavone supplements increases or decreases the effects of estrogen on the body, such as the risk of blood clots. It is unclear if taking soy alters the effectiveness of oral contraceptives containing estrogen.

Selective Estrogen Receptor Modulators (SERMs), Aromatase Inhibitors: It is not known what the effects of soy phytoestrogens are on the anti-tumor effects of selective estrogen receptor modulators (SERMs) such as tamoxifen. The effects of aromatase inhibitors such as anastrozole (Arimidex®), exemestane (Aromasin®), or letrozole (Femara®) may be reduced. Because of the potential estrogen-like properties of soy, people receiving these drugs should speak with their oncologist prior to taking soy in amounts greater than normally found in the diet.

Warfarin (Coumadin®):Soy protein may interact with warfarin, although this potential interaction is not well characterized. Patients taking warfarin should check with a doctor and pharmacist before taking soy supplementation.

Interactions with Herbs and Dietary Supplements

Iron:The effects of soy protein or flour on iron absorption are not clear. Studies in the 1980s reported decreases in iron absorption, although more recent research has noted no effects or increased iron absorption in people taking soy. People using iron supplements as well as soy products should consult a qualified healthcare practitioner to follow blood iron levels.

Panax ginseng: Some experts believe that there may be a potential interaction between soy extract and Panax ginseng although this potential interaction is not well characterized.

Interactions with Laboratory Assays

Calcium, Phosphate: Animal research suggests that soy may possess estrogen-like effects that affect calcium and phosphate levels. Urinary calcium excretion may be reduced. Further study is needed before a firm conclusion can be drawn.

Interactions with Foods

Wheat: Based on limited human study, reduced absorption of the soy isoflavone genistein (theorized to possess "phytoestrogen" properties) may occur when taken in combination with wheat fiber.

About the Author

medlineplus.gov
MedlinePlus will direct you to information to help answer health questions. MedlinePlus brings together authoritative information from NLM, the National Institutes of Health (NIH), and other government agencies and health-related organizations. MedlinePlus also has extensive information about drugs, an illustrated medical encyclopedia, interactive patient tutorials, and latest health news.