Can Selenium Deficiency Cause Weight Gain? The Thyroid Connection

October 23, 2025 •

4 min read

Over 50% of heart failure patients in a European study were found to have low serum selenium levels, which can significantly affect metabolic health. The question, 'Can selenium deficiency cause weight gain?', is pertinent because selenium is vital for the thyroid gland, the body's metabolic regulator.

Quick Summary

Selenium deficiency may contribute to unexplained weight gain by impairing thyroid hormone function and slowing metabolism. The trace mineral is crucial for converting thyroid hormones and protecting the thyroid from oxidative stress, and its absence can lead to metabolic issues similar to hypothyroidism.

Key Points

Thyroid Impairment: Selenium deficiency can lead to weight gain by compromising thyroid function, slowing down metabolism.
Hormone Conversion: The mineral is essential for converting the inactive thyroid hormone T4 into the active form, T3, which regulates metabolic rate.
Antioxidant Role: Selenium protects the thyroid from oxidative stress, and its absence can cause cellular damage and dysfunction.
Variable Evidence: While studies show a link between low selenium and higher body fat, research results can vary depending on dosage, population, and existing health conditions.
Medical Guidance: It is critical to consult a doctor before supplementing with selenium, as both deficiency and excess can pose health risks.

The Crucial Role of Selenium in Metabolism

Selenium is a trace mineral that acts as a powerful antioxidant and is a critical component of selenoproteins. These proteins are involved in many physiological processes, including immune function, DNA synthesis, and most notably, thyroid hormone metabolism. The thyroid gland contains the body's highest concentration of selenium, highlighting its importance for this vital endocrine organ. When selenium levels drop too low, the production and activation of thyroid hormones can be compromised, leading to a cascade of metabolic disturbances.

How Low Selenium Affects Thyroid Hormone Metabolism

Conversion of T4 to T3: The thyroid produces mostly an inactive hormone called thyroxine (T4). For the body to use this hormone, it must be converted into the active form, triiodothyronine (T3). This conversion is done by a group of selenoenzymes called iodothyronine deiodinases. A deficiency in selenium impairs the function of these enzymes, hindering the conversion of T4 to T3.
Oxidative Stress Protection: The process of producing thyroid hormones generates hydrogen peroxide, a reactive oxygen species. Selenoproteins like glutathione peroxidases protect the thyroid gland from oxidative damage caused by this process. Insufficient selenium means less protection, which can damage the thyroid and disrupt its function over time.
Hypothyroid-like Symptoms: The metabolic slowdown resulting from impaired thyroid function can mimic the symptoms of hypothyroidism, a condition known to cause weight gain. A sluggish metabolism burns fewer calories, which can lead to weight gain even if dietary intake remains unchanged.

Scientific Evidence Linking Selenium Deficiency and Weight Gain

Several studies have explored the connection between selenium status and body weight, with some yielding contradictory results due to varying study designs, dosage, and population health. However, a significant body of research points toward a link.

A cross-sectional study on a large adult population in China found an inverse, dose-dependent relationship between dietary selenium intake and body fat percentage. In both men and women, higher selenium intake corresponded to a lower BMI and less body fat.
A randomized prospective study involving overweight and obese individuals showed that those who received selenium supplementation alongside a hypocaloric diet experienced a greater decrease in body fat mass and an increase in lean body mass compared to the placebo group.
Research has shown that lower serum selenium levels correlate directly with a higher waist circumference and higher body fat percentage, particularly in women.

The Importance of Optimal Selenium Intake

It is crucial to understand that both a deficiency and an excess of selenium can have negative health consequences, and the optimal range is narrow. Excessive intake, known as selenosis, can cause serious side effects, including hair loss, nail brittleness, and neurological problems. Therefore, supplementation should always be managed under medical supervision, especially in regions with adequate selenium soil levels.

Comparison of Normal vs. Selenium-Deficient Metabolism


Feature	Normal Selenium Status	Selenium-Deficient Status
Thyroid Hormone Conversion (T4 to T3)	Efficient conversion via active iodothyronine deiodinases.	Impaired conversion due to reduced deiodinase activity.
Antioxidant Protection	High levels of glutathione peroxidase protect thyroid from oxidative stress.	Reduced antioxidant defense, leaving thyroid susceptible to damage.
Metabolic Rate	Balanced metabolic rate maintained by sufficient active thyroid hormones.	Slower metabolism, similar to subclinical hypothyroidism.
Weight Management	Easier to maintain or lose weight due to optimal metabolism.	Unexplained or difficult-to-manage weight gain is more likely.
Overall Energy	Consistent energy levels due to proper metabolic function.	Chronic fatigue and lack of energy are common symptoms.

How to Address a Potential Deficiency

First and foremost, if you suspect a selenium deficiency is affecting your weight, consult a healthcare professional for a proper diagnosis. Blood tests can measure your selenium levels and help determine the right course of action. Do not self-diagnose or begin high-dose supplementation without a doctor's guidance due to the risks of excess intake.

Dietary sources of selenium are the safest way to increase your intake naturally. These include:

Brazil nuts (one or two a day is often enough due to their high concentration).
Meat and poultry.
Fish and shellfish.
Eggs and dairy products.
Enriched breads and cereals.
Sunflower seeds.

Conclusion

While not the sole cause, selenium deficiency can cause weight gain by disrupting the thyroid's ability to regulate metabolism effectively. The mineral's role in converting inactive thyroid hormone (T4) into the active form (T3) and protecting the thyroid from oxidative damage is vital for maintaining a healthy metabolic rate. Individuals with unexplained weight gain, especially those with other symptoms of hypothyroidism or who live in low-selenium areas, should discuss their selenium levels with a doctor. A balanced approach focusing on whole-food sources under professional guidance is the safest path to correcting a deficiency and supporting overall metabolic health. For more on selenium's function, refer to the National Institutes of Health(https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/).

Frequently Asked Questions

Selenium deficiency primarily affects metabolism by disrupting the function of the thyroid gland, the master regulator of the body's metabolic rate. Without enough selenium, the body cannot efficiently convert the inactive thyroid hormone (T4) into its active form (T3), leading to a metabolic slowdown that can cause fatigue and weight gain.

In cases where weight gain is directly linked to an underlying selenium deficiency affecting thyroid function, correcting the deficiency may help reverse the weight gain. Some studies show that supplementation, particularly in conjunction with a healthy diet, can lead to a reduction in body fat mass.

Common symptoms of selenium deficiency include fatigue, hair loss, a weakened immune system, muscle weakness, and in severe cases, more serious conditions like cardiomyopathy. Symptoms related to thyroid dysfunction, such as weight gain and cold intolerance, are also common.

A selenium deficiency is diagnosed by a healthcare professional, typically through a blood test that measures selenium levels. It is important to consult a doctor, as symptoms can overlap with other conditions, and self-diagnosing can be inaccurate.

Excellent food sources of selenium include Brazil nuts, meat and poultry, fish (like tuna and halibut), shellfish, eggs, dairy products, and enriched grains. The selenium content in plant-based foods can vary significantly depending on the soil composition where they were grown.

Taking a selenium supplement solely for weight loss is not recommended without medical advice. While correcting a deficiency may support weight management, excess selenium can be toxic. A doctor should determine if supplementation is necessary and at what dose.

Yes, some research suggests sex-specific differences. A study involving a large cohort found that lower selenium levels were associated with higher BMI and an increased prevalence of diabetes in females, but not in males. This could be related to differing impacts on fat distribution and thyroid function.