Selenium is an essential trace mineral that the human body requires in small amounts for proper function. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps. The connection between selenium intake and blood pressure regulation is complex and has been a subject of considerable scientific investigation. Understanding this relationship involves exploring the mineral’s biological roles, the effects of its varying levels in the body, and how diet and supplementation factor into maintaining a healthy balance.
The Antioxidant Role of Selenium
Selenium’s influence on the body is primarily exerted through its incorporation into a unique group of proteins known as selenoproteins. There are 25 identified human selenoproteins, and many of them function as enzymes with a variety of roles. A principal function of these specialized proteins is to act as antioxidants, which are compounds that protect cells from damage.
One of the most well-studied selenoproteins is glutathione peroxidase (GPx), an antioxidant enzyme. The primary job of GPx is to neutralize excessive reactive oxygen species (ROS), which are unstable molecules that can cause damage to cells, proteins, and DNA through a process called oxidative stress. Unchecked oxidative stress contributes to chronic inflammation, a state that can harm the delicate inner lining of blood vessels, known as the endothelium.
This damage to the endothelium is a factor in the development and progression of hypertension, or high blood pressure. A compromised endothelium loses its ability to properly regulate vascular tone, the contraction and relaxation of blood vessels that helps control blood flow and pressure. By supporting the function of enzymes like GPx, selenium helps to mitigate oxidative stress and inflammation, thereby protecting vascular integrity and function.
Impact of Selenium Levels on Blood Pressure
The relationship between the amount of selenium in the body and its effect on blood pressure is not straightforward. Research suggests a complex, U-shaped or biphasic association, meaning that both too little and too much selenium can be detrimental. Both selenium deficiency and selenium excess have been correlated with an increased prevalence of hypertension in various studies.
Studies have shown that in populations with low selenium status, supplementation can sometimes help manage conditions associated with deficiency, such as certain types of heart muscle disease. In these cases, restoring selenium to adequate levels supports the body’s antioxidant defenses, which can have a beneficial impact on the cardiovascular system. However, the benefits appear to plateau once selenium concentrations are sufficient.
Conversely, in populations where selenium intake is already adequate or high, such as in the United States, studies have observed a different trend. Research analyzing data from the National Health and Nutrition Examination Survey (NHANES) found that higher serum selenium concentrations were associated with a greater prevalence of hypertension. For instance, one analysis showed that individuals with serum selenium levels at or above 120 μg/L had a significantly higher association with hypertension.
Dietary Selenium and Supplementation
Most individuals can achieve adequate selenium intake through a well-rounded diet, as the mineral is present in a variety of foods. The amount of selenium in plant-based foods, such as grains and vegetables, is highly dependent on the selenium content of the soil in which they were grown. This can lead to significant geographic variation in the selenium content of local produce.
Excellent dietary sources of selenium include:
- Brazil nuts
- Seafood like tuna and shellfish
- Organ meats
- Muscle meats from poultry and beef
- Eggs
- Whole grains
- Dairy products
The Recommended Dietary Allowance (RDA) for selenium for most adults is 55 micrograms (mcg) per day, with slightly higher recommendations for pregnant and lactating women. In the United States, the average daily intake from food alone often exceeds this recommendation, typically ranging around 108 mcg.
Given that most people meet their selenium needs through food, supplementation is generally not necessary unless a specific deficiency has been diagnosed by a healthcare provider. It is important to consider all sources, including fortified foods and multivitamins, when assessing total selenium consumption to avoid unintentionally exceeding safe levels.
Understanding Selenium Toxicity
Consuming too much selenium can lead to a toxic condition known as selenosis. This condition is almost exclusively caused by taking high-dose supplements over a prolonged period, rather than from dietary sources alone. A notable exception is the overconsumption of Brazil nuts, which are exceptionally high in selenium; a single ounce (about 6-8 nuts) can contain more than 544 mcg, far exceeding the daily recommended amount.
The Tolerable Upper Intake Level (UL) for selenium for adults is set at 400 micrograms per day from all sources. Regularly consuming amounts above this level increases the risk of developing symptoms of toxicity. Early signs of selenosis can include a distinct garlic-like odor on the breath, a metallic taste in the mouth, nausea, and diarrhea.
If excessive intake continues, more severe symptoms can develop. These may include hair loss, brittle or discolored nails, skin rashes or lesions, fatigue, and irritability. In more advanced cases, neurological issues such as dizziness, motor weakness, or a burning or prickling sensation in the extremities can occur.