Selenium is an essential trace mineral, often obtained through diet, that the human body requires for proper function. This micronutrient is incorporated into numerous proteins, known as selenoproteins, which play varied roles in health. The question of whether selenium intake, particularly from supplements, affects blood pressure is common, given its involvement in cardiovascular processes.
Selenium’s Role in Vascular Function
Selenium’s primary function in the circulatory system is tied to its role in forming selenoproteins, such as glutathione peroxidases (GPx). These selenoproteins are powerful components of the body’s antioxidant defense system. They work to neutralize harmful molecules called reactive oxygen species (ROS), thereby reducing oxidative stress within blood vessels. This action helps maintain a healthy internal environment.
Blood pressure regulation relies heavily on the health of the endothelium, the inner lining of all blood vessels. Oxidative stress can damage this lining, leading to endothelial dysfunction and impaired vasodilation. Selenium supports normal vascular function by protecting the endothelium from this damage, allowing blood vessels to widen and lower pressure.
This protective action is a mechanism by which adequate selenium levels support the body’s natural ability to regulate blood flow and pressure. For instance, the selenoprotein GPx3 is active outside of cells and helps regulate endothelial function.
Current Scientific Consensus on Blood Pressure Effects
The effects of selenium on blood pressure are highly dependent on the individual’s initial status and the dose consumed. Most scientific evidence suggests that deficiency is more likely to negatively impact blood pressure than optimal intake. Studies in animal models have shown that long-term selenium deficiency can cause hypertension, partially by increasing oxidative stress and impairing the kidneys’ ability to excrete sodium.
In human populations, epidemiological studies on the link between selenium levels and hypertension have yielded contradictory results. Some analyses have shown that higher baseline selenium concentrations were associated with a lower risk of developing high blood pressure. Other studies, however, have found that very high serum selenium levels correlated with an increased prevalence of hypertension.
A systematic review and meta-analysis of randomized controlled trials involving supplementation found that selenium intake significantly increased systolic blood pressure by a small amount. This finding reinforces the idea that while low selenium is detrimental, increasing levels above the point of sufficiency may be counterproductive for blood pressure control. The current scientific understanding points toward a U-shaped relationship, where both too little and too much selenium may be associated with negative health outcomes.
Symptoms and Dangers of Excessive Selenium Intake
Excessive intake of selenium leads to selenosis, the toxic end of the spectrum. The Tolerable Upper Intake Level (UL) for adults is 400 micrograms (µg) per day, and symptoms typically occur when this limit is regularly exceeded. Early signs of toxicity often include a metallic taste in the mouth and breath that smells like garlic.
As toxicity progresses, symptoms develop, such as hair loss, nail brittleness, and deformation. Gastrointestinal issues like nausea and diarrhea are also common. Severe, life-threatening cardiovascular complications are rare, but they are associated with extreme, acute overdoses.
Selenosis usually results from high-dose dietary supplements or the overconsumption of selenium-rich foods, like Brazil nuts. Chronic overexposure can also occur in rare instances of environmental exposure, such as areas with extremely high soil selenium. Maintaining intake below the UL is the most effective way to prevent chronic selenium toxicity.
Guidelines for Safe Dietary Intake
To ensure adequate intake without risking toxicity, adults should aim for the Recommended Dietary Allowance (RDA) of 55 µg of selenium per day. Most people meet this requirement through their regular diet alone. The maximum daily intake considered safe, the UL, is 400 µg for adults.
Natural foods are the best sources of this trace mineral, generally providing selenium in a safe and balanced way. Brazil nuts are an exceptional source, with just one nut potentially containing more than the daily RDA.
Other reliable sources include:
- Seafood, such as tuna and halibut.
- Lean meats.
- Eggs.
- Whole grains.
Individuals concerned about their selenium status should consult a healthcare provider before starting supplementation. Supplements often contain doses ranging from 100 to 400 µg, which can quickly push total daily intake over the safe upper limit. Supplementation is typically only recommended for those with confirmed deficiency, which is uncommon in North America.