Quercetin, a widely recognized plant compound, has gained attention for its potential health benefits. As interest in natural supplements grows, questions arise regarding their interactions with the body’s systems, including the thyroid gland. This article explores the current scientific understanding of whether quercetin can contribute to or cause hypothyroidism.
What is Quercetin?
Quercetin is a plant pigment, a flavonol, found in various fruits, vegetables, and grains. Dietary sources include onions, apples, berries, green tea, and capers. It is studied for its potent antioxidant and anti-inflammatory properties, supporting cardiovascular health and reducing inflammation. The human body cannot produce this naturally occurring substance. While consumed through diet, it is also available as a dietary supplement and is generally considered safe for short-term use at typical doses.
Understanding Hypothyroidism
Hypothyroidism is an underactive thyroid gland that does not produce enough thyroid hormones. These hormones regulate the body’s metabolism and energy use. Symptoms often develop slowly and can include fatigue, unexplained weight gain, increased sensitivity to cold, dry skin, constipation, and difficulty concentrating.
The most common cause is Hashimoto’s disease, an autoimmune condition. Other causes include iodine deficiency or certain medications. Untreated hypothyroidism can lead to various health complications.
Quercetin and Thyroid Function
Current scientific understanding suggests that quercetin does not cause hypothyroidism in humans. Human studies and clinical trials have not reported hypothyroidism as a side effect. Instead, research indicates that quercetin may have neutral or beneficial effects on thyroid function, due to its antioxidant and anti-inflammatory properties.
Some animal studies, however, have shown that quercetin can interact with thyroid function at high doses. For example, in vitro (cell culture) and in vivo (animal) studies have observed that quercetin can inhibit thyroid cell growth, reduce iodide uptake, and downregulate genes involved in thyroid hormone synthesis (NIS, TG, TPO). These effects also include inhibition of deiodinase type 1 (D1) activity, an enzyme converting T4 into T3.
Findings from animal studies and cell cultures, especially those using very high concentrations, do not always directly translate to the human body or typical dietary intake levels. The average daily intake of quercetin from food is considerably lower than the high doses sometimes used in experimental settings. While some experimental studies suggest caution with “excessive intake” due to potential interference, this concern primarily arises from high-dose animal and in vitro models, not typical human consumption or supplementation.
Quercetin’s antioxidant and anti-inflammatory actions may offer theoretical benefits for thyroid health, particularly in autoimmune conditions like Hashimoto’s thyroiditis, by reducing oxidative stress and inflammation within the thyroid gland. Some research also explores a potential therapeutic role for quercetin in thyroid cancer, where it inhibits cancer cell growth and promotes redifferentiation. However, more direct human research is necessary to fully understand these potential benefits.
Important Considerations
Individuals considering quercetin supplementation, particularly those with pre-existing thyroid conditions or taking thyroid medication, should consult a healthcare professional. A doctor can provide personalized advice and assess potential interactions with current medications or health conditions. Self-diagnosis or self-treatment based solely on online information is not recommended.
While quercetin is generally considered safe for most people when used in moderate amounts for short periods, individual responses to supplements can vary. Some quercetin supplements might contain other ingredients, such as kelp, a source of high iodine. Excessive iodine intake can sometimes affect thyroid function, making it important to be aware of all ingredients in any supplement. Consulting with a healthcare provider ensures that supplementation decisions are made safely and appropriately for individual health needs.