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Moderate evidenceWomen's health

Genistein

The isolated soy isoflavone with the most bone data behind it. Effects on bone density are consistent but small, and menopausal symptom relief is real but modest.

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What the science says

  • Bone mineral density Moderate evidence

    A follow-up of a randomized trial of genistein aglycone in postmenopausal women with bone loss reported increases in bone mineral density over three years without adverse breast effects, and a systematic review and meta-analysis of isoflavone trials found a small overall benefit for bone mineral density.

  • Menopausal symptoms Moderate evidence

    A multi-center randomized placebo-controlled trial of synthetic genistein in healthy postmenopausal women reported reduced hot flash frequency. The size of the effect is smaller than with hormone therapy.

Dosage & safety

Studied doseBone trials used 54 mg of genistein aglycone daily; menopause symptom trials used around 30 mg daily. Effects on bone were seen over 12-36 months.
SafetyDigestive upset is the most common complaint. Genistein is estrogenic, and although trial follow-up found no adverse breast effects, women with hormone-sensitive cancers or on tamoxifen should not self-prescribe it. Avoid in pregnancy and breastfeeding; may interfere with thyroid function at high intakes when iodine is low.

How to take it

TimingTiming does not matter.
With food?With food.
Worth knowingBone density changes took 12 to 36 months in the trials, so this is not something to judge over a few weeks.

Interactions

With medications

  • tamoxifen and aromatase inhibitors

    Genistein is estrogenic and may work against endocrine therapy. do not self-prescribe it during breast cancer treatment

  • levothyroxine

    Soy isoflavones reduce levothyroxine absorption. separate by at least 4 hours and keep intake consistent

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does genistein improve bone density?

Yes, but the effect is small: a randomized trial of genistein aglycone in postmenopausal women with bone loss reported bone density increases over three years without adverse breast effects, and a meta-analysis found a small benefit. The evidence grade is moderate.

Does genistein help hot flashes?

A multi-centre randomized placebo-controlled trial found synthetic genistein reduced hot flash frequency in postmenopausal women, a moderate-grade result. The effect is smaller than with hormone therapy.

How much genistein should I take?

Bone trials used 54 mg of genistein aglycone daily and menopause symptom trials used around 30 mg daily. Bone changes took 12 to 36 months, so genistein cannot be judged over a few weeks.

Is genistein safe with thyroid medication or tamoxifen?

Genistein reduces levothyroxine absorption, so separate them by at least 4 hours and keep intake consistent. It is estrogenic and may work against tamoxifen or aromatase inhibitors, so do not self-prescribe it during breast cancer treatment.

Scientific references

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