The Dual Nature of Selenium: A Non-Linear Relationship
Studies on US adults have consistently shown that the relationship between dietary selenium intake and chronic disease risk is often U-shaped or curvilinear. This means moderate intake is associated with reduced risk for certain chronic diseases and mortality, while both deficiency and very high intake levels can be harmful.
Associations with Cardiovascular Disease
Recent analyses, including those utilizing NHANES data, have investigated the link between dietary selenium and cardiovascular disease (CVD). A consistent inverse relationship has been observed between moderate selenium intake and a lower risk of CVD, including coronary heart disease (CHD), stroke, and atherosclerotic cardiovascular disease (ASCVD). This protective effect on heart health shows a clear nonlinear trend, potentially weakening or reversing at intake levels above around 135 µg/day.
The Complex Link to Cancer
The association between selenium and cancer risk is widely studied. While some observational studies show an inverse relationship, randomized controlled trials (RCTs) have yielded mixed results, particularly with supplementation. Observational data has suggested that higher dietary selenium intake is associated with a lower risk of certain cancers. However, trials like SELECT found no beneficial effect of selenium supplementation on prostate cancer risk and raised concerns about potential increased risk for other issues, highlighting differences between selenium from food and supplements.
Effects on Other Chronic Conditions and Overall Mortality
Selenium's influence extends to other chronic conditions and overall longevity.
- Diabetes: Research suggests a complex association with diabetes risk. Insufficient levels may increase risk, while long-term, high-dose supplementation has been linked to a higher risk of developing type 2 diabetes.
- Sarcopenia: A study of US adults showed an inverse relationship between dietary selenium intake and the prevalence of sarcopenia.
- Mortality: The nonlinear association with mortality is also evident. Moderate dietary selenium appears protective against all-cause mortality, particularly for adults over 50, but the highest levels may not offer further benefits.
Comparison of Selenium Intake and Health Outcomes
| Health Outcome | Effect at Low Intake | Effect at Moderate Intake | Effect at High Intake (Excessive) |
|---|---|---|---|
| Cardiovascular Disease | Potential increased risk | Decreased risk of CVD, stroke, ASCVD | Protective effects may weaken or reverse |
| Cancer | Potential increased risk in deficient populations | Mixed results; observational link to lower risk | Supplementation has shown no benefit and potential harm |
| All-Cause Mortality | Increased risk associated with deficiency | Protective effect, especially over age 50 | Protective effect may diminish or reverse |
| Type 2 Diabetes | Potential increased risk | No significant association found consistently | Increased risk of development linked to long-term supplementation |
| Sarcopenia (Muscle Loss) | Increased prevalence linked to lower intake | Lower prevalence observed | No clear association documented in cited studies |
Nutritional Strategies for Balancing Selenium
For US adults with generally sufficient intake, focusing on dietary balance over supplementation is recommended.
Key strategies include:
- Incorporate selenium-rich foods: Prioritize foods high in selenium.
- Moderate Brazil nut consumption: Brazil nuts are very high in selenium; a few per week can be sufficient.
- Diversify protein sources: Include seafood, poultry, and eggs.
- Choose whole grains and legumes: These are also good sources.
Conclusion
The associations between dietary selenium, chronic disease, and mortality in US adults are complex and often non-linear. Moderate dietary intake, typically from a balanced diet, is linked to reduced risk of CVD, sarcopenia, and overall mortality. However, exceeding certain thresholds, particularly via high-dose supplementation, may increase risks for conditions like type 2 diabetes and certain cancers. The evidence supports a balanced dietary approach to maintain optimal selenium status, rather than relying on supplements unless a deficiency is diagnosed. Further research is ongoing.
For more information on selenium and disease, the NIH Office of Dietary Supplements is a valuable resource.
