Who Shouldn't Take Polyphenols? Key Considerations and Risks

November 29, 2025 •

3 min read

While dietary polyphenols are generally safe and beneficial for most people, some populations need to exercise caution, especially with supplements. A high-dose polyphenol supplement may interact with medications or cause adverse effects in individuals with pre-existing conditions. It is critical to understand who shouldn't take polyphenols to prevent unintended health consequences.

Quick Summary

Individuals with certain health conditions or those on specific medications should be cautious with high doses of polyphenols, particularly from supplements. Risks include impaired iron absorption, thyroid hormone disruption, and drug interactions, with whole foods generally safer than isolated compounds found in high-dose supplements.

Key Points

Iron Deficiency Anemia: Individuals with low iron levels should be cautious, as high polyphenol intake can inhibit the absorption of non-heme iron from plant-based foods.
Thyroid Conditions: People with thyroid disorders, especially hypothyroidism or Hashimoto's, should seek medical advice, as some flavonoids can interfere with thyroid hormone synthesis.
Medication Interactions: Polyphenols can alter the effects of certain medications, such as blood thinners and certain heart medications; consult a doctor or pharmacist for personalized advice.
Pregnant or Breastfeeding Individuals: High-dose polyphenol supplements are not recommended for pregnant or breastfeeding women due to limited safety data.
Digestive Sensitivity: People with sensitive digestive tracts or conditions like IBS might experience gastrointestinal issues, including bloating and gas, from high intake of certain polyphenol-rich foods or supplements.
Prioritize Whole Foods Over Supplements: Whole foods provide a balanced nutrient profile and lower, safer doses of polyphenols compared to concentrated, unregulated supplements.

Polyphenols and Iron Deficiency

One of the most well-documented risks of high polyphenol intake, particularly from supplements, is its effect on iron absorption. Polyphenols can bind to non-heme iron (the form found in plant-based foods) in the gastrointestinal tract, creating a complex that the body cannot absorb effectively. This inhibitory effect is especially concerning for individuals with existing iron deficiency anemia, pregnant women, and young children who may have low or marginal iron stores. To mitigate this issue, individuals can separate their intake of polyphenol-rich foods and iron supplements, or consume iron-rich meals separately from foods high in polyphenols like tea, coffee, or cocoa.

Thyroid Function Concerns

Some flavonoids, a class of polyphenols, have been shown to interfere with thyroid function. Research indicates that certain flavonoids can inhibit thyroperoxidase (TPO) activity, an enzyme crucial for producing thyroid hormones, potentially leading to or worsening hypothyroidism, especially in individuals with low iodine levels. While this is primarily a concern with high-dose supplements, individuals with thyroid disorders like Hashimoto's should discuss their polyphenol intake with a healthcare professional. In contrast, some polyphenols may have beneficial anti-inflammatory effects for those with Hashimoto's, highlighting the complexity and need for personalized medical advice.

Digestive Issues and Sensitivity

Although polyphenols can promote gut health by acting as prebiotics, high concentrations, especially from supplements or large quantities of certain foods, can cause digestive upset in some people. Foods like beans, peas, and berries, which contain polyphenols, can also be high in lectins or fiber, which may cause gas, bloating, and indigestion when consumed in large amounts. People with sensitive digestive systems, including those with conditions like Irritable Bowel Syndrome (IBS), might need to monitor their intake of these specific food sources.

Potential Medication Interactions

Polyphenols can interfere with the metabolism and effectiveness of certain medications. For example, grapefruit juice contains specific polyphenols that are well-known to interact with numerous drugs, including certain statins and blood pressure medications. Similarly, polyphenols like curcumin (from turmeric) or grape seed extract can have anticoagulant properties, which may increase the risk of bleeding in individuals taking blood-thinning medications like warfarin. Anyone on a prescription medication should consult their doctor or pharmacist about potential interactions before taking high-dose polyphenol supplements.

Pregnancy and Breastfeeding

Due to the lack of sufficient reliable information on the effects of high-dose polyphenol supplements, pregnant and breastfeeding individuals are advised to avoid them. While consuming polyphenol-rich whole foods is generally considered safe and encouraged as part of a balanced diet, the concentrated amounts found in supplements may pose unknown risks to both the mother and baby. It is always recommended to prioritize whole-food sources and consult a healthcare provider for any questions regarding supplements during this time.

Comparison of Polyphenol Intake: Whole Foods vs. Supplements


Feature	Polyphenol-Rich Whole Foods	Polyphenol Supplements
Polyphenol Concentration	Varies, typically lower concentrations	Standardized and concentrated dosages, often very high
Nutrient Synergy	Polyphenols work synergistically with other vitamins, minerals, and fibers.	Isolated compounds may not have the same synergistic effects.
Absorption Rate	Slower, with gut microbiota playing a key role in metabolism.	Potentially rapid absorption of high doses, overwhelming metabolic pathways.
Risk of Overconsumption	Low risk; difficult to consume excessive amounts	High risk with unregulated, high-dose products.
Risk of Side Effects	Generally low for most people; mild digestive issues possible.	Higher risk of adverse effects like liver injury, iron deficiency, or thyroid disruption.
Regulatory Oversight	Food regulation applies; generally recognized as safe.	Often unregulated; dosages may not be scientifically validated.

Conclusion

While a diet rich in polyphenols from whole foods is a cornerstone of a healthy lifestyle, the concentrated and isolated nature of polyphenol supplements warrants significant caution for specific individuals. Those with iron deficiency, thyroid conditions, or who take certain prescription medications face legitimate risks that can be exacerbated by high-dose supplementation. Additionally, pregnant and breastfeeding women, and those with sensitive digestive systems, should prioritize whole foods over supplements to avoid potential harm. As research continues to uncover the complex interplay between polyphenols, nutrient absorption, and drug metabolism, personalized medical guidance is essential. The safest and most effective approach for most people remains deriving polyphenols from a diverse diet of fruits, vegetables, and other whole plant-based foods.

Frequently Asked Questions

Some studies, particularly on high-dose green tea extract supplements, have linked excessive intake of isolated polyphenols to potential hepatotoxicity, or liver damage. The risk is associated with unregulated, concentrated supplements, not with consuming polyphenols from a healthy diet.

For most people, getting polyphenols from whole foods is safer and more beneficial. Foods provide a natural balance of nutrients, fiber, and other compounds that work synergistically with polyphenols. Supplements contain high, isolated doses that may not be as effective and carry higher risks.

Polyphenols can interact with enzymes and drug transporters in the body, which can increase or decrease the effectiveness of certain medications. A notable example is grapefruit juice, which interacts with a wide range of common prescriptions.

While research shows some polyphenols may protect kidney health, the evidence is not yet conclusive, and isolated supplements have shown minimal effects on renal function in studies. Individuals with chronic kidney disease should consult their doctor before taking polyphenol supplements.

Yes, while polyphenols are known for their antioxidant properties, some studies show that at very high concentrations, they can exhibit pro-oxidative effects. This is primarily a concern with high-dose supplements rather than normal dietary intake.

The most common side effects from high intake, particularly from supplements, include mild gastrointestinal upset such as diarrhea, gas, and bloating. Other risks include impaired iron absorption and potential interactions with medications.

To enhance iron absorption, try consuming polyphenol-rich foods and beverages like coffee or tea at a different time than your iron-rich meals or supplements. Pairing iron sources with vitamin C-rich foods can also help counteract the inhibitory effects of polyphenols.