Phytoestrogens, isoflavones and menopause supplements: what works and what doesn't

Hot flushes, insomnia, mood changes. When menopause arrives, many women look for an alternative at the pharmacy or the health food shop: soy phytoestrogens, isoflavones, vitamins, fish oil. The promise sounds good and taking them feels harmless. But it is worth separating two things that often get muddled: what a supplement can actually do according to the evidence, and what a label is legally entitled to promise you. This article is educational: it explains what is known and what is not, without recommending any particular product.

What a supplement is (and what it cannot promise you)

According to AESAN, food supplements are foodstuffs consisting of concentrated sources of nutrients intended to supplement the intake of a normal diet. The key word is food: legally they are foods, not medicines. That difference is not a technicality; it shapes everything a product can or cannot tell you.

In the European Union the regulatory frameworks for foods and medicines are mutually exclusive: any claim that a product treats or prevents a disease classifies it as a medicine, with all the requirements that entails. That is why a menopause supplement cannot state on its label that it treats hot flushes: if it did, it would stop being a supplement. When you read vague phrases along the lines of contributes to wellbeing, that woolly language is usually the sign that there is no specific authorised health claim behind it.

Health claims have to be authorised

Not every benefit can appear on a label. All authorised nutrition and health claims have had to go through a procedure demonstrating that they are based on sound scientific data, assessed by EFSA and authorised at European level. Only those listed in the EU Register of authorised claims may be used. In the case of botanicals, which is where the plants behind many menopause products come in, the story is telling: more than 2,000 botanical claims were put on hold by the Commission in 2010 and remain so, unassessed and under transitional rules; meanwhile, the EFSA panel issued negative opinions on many other claims, including some on botanicals, which were not authorised.

Phytoestrogens and isoflavones: what the evidence allows you to say

Soy and red clover isoflavones are what we call phytoestrogens: plant-derived compounds with some structural similarity to oestrogens. Hence the popular idea that they might relieve menopause symptoms. What matters for the consumer, however, is that within the European framework these botanical compounds have no authorised health claims backing specific treatment statements, and so no product can legally claim to treat a symptom. That gap between what is promised by word of mouth and what can be stated in writing is, in itself, worth knowing about.

This does not mean research has stopped, but rather that the regulatory bar for claiming a health benefit is high and many botanicals have not cleared it. The distance between perception and evidence also shows up in how the people taking them see them: in the Spanish cross-sectional RENHYD study, supplements were perceived as safe but with mild, short-lived effectiveness.

Vitamins, omega-3 and vitamin D: what the big trials say

Many menopause products include vitamins and other nutrients with the implicit idea of protecting bones, the heart or general health. Here it is worth looking at the large trials, because they dismantle several myths with hard data.

On multivitamins and minerals, the evidence review carried out for the US Preventive Services Task Force by O'Connor's team (JAMA, 2022) concluded that supplementation is associated with little or no benefit in preventing cancer, cardiovascular disease and death, with the exception of a small benefit in cancer incidence with multivitamins; the USPSTF itself judged the evidence insufficient to recommend for or against them. It went further and recommended against the use of beta-carotene or vitamin E supplements to prevent cardiovascular disease or cancer (grade D recommendation), and warned that beta-carotene was associated with an increased risk of lung cancer in high-risk people.

Fish oil (omega-3) is another classic. In the large VITAL trial, with 25,871 participants and a mean follow-up of 5.3 years, supplementation with n−3 fatty acids at 1 g/day did not reduce major adverse cardiovascular events or cancer compared with placebo. In the same trial, vitamin D at 2,000 IU daily also showed no benefit in preventing major adverse cardiovascular events or cancer.

Vitamin D deserves an honest nuance, because headlines tend to oversimplify it. In cardiovascular prevention, the VITAL trial (25,871 participants, 5.3 years of follow-up) showed no difference versus placebo in major cardiovascular events (HR 0.97; 95% CI 0.85–1.12), so there is no basis for recommending it for that purpose. On the other hand, a 2014 Cochrane review found that vitamin D3 significantly reduced cancer mortality (RR 0.88; 95% CI 0.78–0.98; 44,492 participants; 4 trials), a small difference in absolute terms. A real benefit in one area, no benefit in another: supplements are not good or bad as a block.

Not harmless: the harms are documented too

The idea that a supplement will at worst do nothing is false. The same Cochrane review found that vitamin D3 combined with calcium increased the risk of nephrolithiasis (kidney stones), with an RR of 1.17 (95% CI 1.02–1.34), and that alfacalcidol and calcitriol increased the risk of hypercalcaemia (RR 3.18; 95% CI 1.17–8.68). Spain's consumer organisation OCU has warned precisely about the mistaken belief that they are harmless, useful for anyone and full of valuable properties. It also points out that, in general, supplements are only needed in specific situations such as pregnancy or a vegan diet.

How they are used in Spain

Use is very widespread. According to OCU (2021), 4 in 10 people in Spain turn to these products, often without professional supervision, and 42% say they have taken them in the past 12 months. The cross-sectional RENHYD study (2022) puts the figure at 75.1% of the population over the past year, of whom 28.6% took plant extracts. There is an even higher estimate, around 80%, but it comes from an industry source (Ipsos/AFEPADI, 2022) and should be treated with caution given that conflict of interest.

As for safeguards, supplement labelling is harmonised by Regulation (EU) 1169/2011 on food information to consumers, and in Spain companies marketing these products are required to notify them. Maximum permitted intake levels for vitamins and minerals assessed by EFSA also apply, and when there is doubt as to whether an ingredient should be authorised as a medicine, AESAN consults the AEMPS, the Spanish Agency for Medicines and Medical Devices.

In summary

The takeaway: menopause supplements sell well, but they promise little in writing, and the evidence from the large trials is modest or non-existent on several fronts; they are neither medicines nor free of risk. Faced with that uncertainty, what does exist in Spain today is a medical approach to the symptoms: menopause treatment with a prior assessment, a prescription where appropriate from a registered doctor, and ongoing follow-up. If you would rather start from a proper assessment than from whichever box is on the shelf, you can check whether you are eligible in a few minutes.