Can Soy Foods or Isoflavones Help with Sleep During Menopause?
Sleep difficulties are common during menopause. Fluctuating and declining estrogen and progesterone levels can affect mood and temperature regulation, while hot flashes and night sweats may interrupt sleep.
Stress, anxiety, depression, pain, medications, nighttime urination, and restless legs can also contribute. Obstructive sleep apnea may become more common during the menopausal transition (1). Because these factors often overlap, poor sleep should not be attributed to hormones alone.
What Does the Research Say About Isoflavones and Sleep?
Soy contains isoflavones, plant compounds with weak estrogen-like activity. Researchers have studied whether these compounds can help reduce hot flashes and improve sleep.
In a double-blind, placebo-controlled study, 38 postmenopausal women with insomnia received either 80 mg of isoflavones daily or a placebo for four months (2).
Sleep monitoring showed that sleep efficiency—the percentage of time in bed spent asleep—increased from 77.9% to 83.9% in the isoflavone group, compared with 77.6% to 81.2% in the placebo group. Isoflavones led to a significantly greater improvement.
The proportion of women reporting moderate or severe insomnia fell from 89.5% to 36.9% with isoflavones, compared with 94.7% to 63.2% with placebo. Isoflavones also reduced hot flash frequency and intensity.
These results suggest that isoflavones may help improve sleep in postmenopausal women. However, the study was small, so the findings should be interpreted cautiously.
Can Soy Foods Help Reduce Hot Flashes?
Another randomized study included 38 postmenopausal women experiencing at least two hot flashes daily. Participants followed either a low-fat vegan diet with ½ cup (86 g) of cooked soybeans daily or their usual diet for 12 weeks (3).
Total hot flashes decreased by 79% in the diet group, compared with 49% in the control group. Moderate-to-severe hot flashes decreased by 84% versus 42%, respectively. Both reductions were significantly greater in the diet group.
By the end of the study, 59% (10 of 17) of participants in the diet group were free of moderate-to-severe hot flashes, while the control group showed no change in this outcome. Participants in the diet group also reported greater improvements in menopause-related physical, psychosocial, and sexual well-being.
Reducing nighttime hot flashes could make sleep less disrupted. However, this study examined hot flashes and quality of life rather than directly measuring sleep. It also tested soybeans and a low-fat vegan diet together, so the benefits cannot be attributed to soybeans alone.
How Much Isoflavone Do Soy Foods Provide?
Tofu, tempeh, edamame, and unsweetened soy milk can provide protein and other nutrients as part of a balanced diet. They also supply isoflavones, although the amounts vary considerably by product, soybean variety, and preparation.
The following estimates use rounded average values from the USDA isoflavone database (4).
Food | Approximate isoflavone content | Amount providing about 80 mg from that food alone |
Firm tofu | 30 mg per 100 g (3½ oz) | 265 g (9⅓ oz) |
Cooked tempeh | 36 mg per 100 g | 225 g (8 oz) |
Cooked, shelled edamame | 18 mg per 100 g | 445 g (about 3 cups) |
Soy milk* | 26 mg per cup (240 mL) | About 3 cups |
The soy-milk estimate includes original and vanilla products and is not specific to every unsweetened brand.
Combining different soy foods throughout the day is another way to reach approximately 80 mg. For example:
150 g firm tofu: about 45 mg
½ cup cooked, shelled edamame (75 g): about 13 mg
1 cup soy milk: about 26 mg
Together, these provide an estimated 84 mg of isoflavones.
The 80 mg dose was tested in the insomnia study; it is not an established daily requirement. These food estimates also do not guarantee the same effects as the study’s supplement. Soy foods can be a nutritious dietary choice, but the evidence is not yet strong enough to promise better sleep. Women considering concentrated isoflavone supplements should discuss their suitability with a healthcare professional, particularly if they take medications or have ongoing medical conditions.
References:
Mirer AG, Young T, Palta M, et al. Sleep-disordered breathing and the menopausal transition among participants in the Sleep in Midlife Women Study. Menopause. 2017;24(2):157–162.
Hachul H, Brandão LC, D’Almeida V, et al. Isoflavones decrease insomnia in postmenopause. Menopause. 2011;18(2):178–184.
Barnard ND, Kahleova H, Holtz DN, et al. The Women’s Study for the Alleviation of Vasomotor Symptoms: a randomized, controlled trial of a plant-based diet and whole soybeans for postmenopausal women. Menopause. 2021;28(10):1150–1156.
U.S. Department of Agriculture, Agricultural Research Service. USDA Database for the Isoflavone Content of Selected Foods, Release 2.1. November 2015.
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