A 20-Year Chinese Study Reveals Surprising Results
The trace mineral in your diet could be the key to maintaining healthy blood pressure.
Imagine a world where a simple dietary adjustment could help millions manage their blood pressure. For decades, scientists have puzzled over the relationship between selenium—an essential trace mineral—and hypertension. Some studies suggested benefits, others found no effect, and a few even pointed to potential harms. This scientific contradiction set the stage for a groundbreaking 20-year Chinese study that would finally shed light on this complex relationship, revealing that the answer isn't as straightforward as we might hope. 1
Selenium is a crucial trace element that our bodies require in small amounts but cannot produce independently. We obtain it primarily through food, with Brazil nuts, seafood, organ meats, and cereals being rich sources. Once ingested, selenium incorporates into vital proteins called selenoproteins, which serve as powerful antioxidants that protect our cells from damage caused by free radicals. 2
These selenoproteins, particularly glutathione peroxidase, play significant roles in reducing oxidative stress and inflammation throughout the body—both of which are key contributors to the development and progression of hypertension.
The connection between selenium and blood pressure regulation represents a fascinating intersection of nutrition and cardiovascular health. Research has shown that selenium deficiency can lead to increased oxidative stress in blood vessels, potentially causing them to constrict and stiffen, thereby raising blood pressure. 3
To unravel the selenium-hypertension mystery, researchers turned to the China Health and Nutrition Survey (CHNS), a comprehensive project that tracked the health and dietary patterns of thousands of Chinese adults over two decades. Published in 2021, this landmark research followed 13,668 participants from 1991 to 2011, specifically examining whether dietary selenium intake influenced their risk of developing hypertension. 4
Participants
Years Duration
New Hypertension Cases
Provinces Covered
The CHNS investigation represents a masterpiece in nutritional epidemiology, combining long-term follow-up with precise dietary assessment. Here's how the researchers conducted this important study:
The study employed a multistage random cluster sampling method across nine diverse provinces in China. This approach ensured representation from various geographic, economic, and cultural backgrounds, making the findings more generalizable to the broader Chinese population.
Participants underwent regular follow-up assessments every 2-4 years, with comprehensive data collection including dietary recalls, physical examinations, and lifestyle questionnaires. This longitudinal design allowed researchers to track how changes in selenium intake correlated with hypertension development over time. 5
Unlike many studies that rely on approximate food frequency questionnaires, the CHNS used detailed three-day food weighing measurements. Trained investigators visited households to weigh and record all food consumed from household stock, purchases, garden produce, and even food waste. This meticulous approach provided unprecedented accuracy in estimating actual selenium consumption. 6
The study yielded surprising results that helped explain previous contradictions in selenium research:
In northern China—a known low-selenium zone—higher selenium intake was associated with reduced hypertension incidence.
In southern China—where soil selenium levels are adequate—additional selenium provided no protective benefit against hypertension.
| Selenium Intake (μg/day) | Hypertension Incidence (per 1000 person-years) |
|---|---|
| 21.0 ± 5.1 | 30.1 |
| 33.2 ± 2.8 | 30.5 |
| 43.8 ± 3.6 | 30.6 |
| 68.3 ± 25.2 | 31.2 |
Source: China Health and Nutrition Survey (1991-2011) 7
| Trajectory Group | Description | Hazard Ratio for Hypertension |
|---|---|---|
| Group 1 | Stable low intake | 1.00 (Reference) |
| Group 2 | Moderate increasing | 0.89 |
| Group 3 | High stable | 0.85 |
| Group 4 | High decreasing | 0.82 |
Source: China Health and Nutrition Survey (1991-2011) 8
After following participants for over 1.2 million person-years and documenting 4,039 new hypertension cases, researchers discovered that selenium's benefits depended entirely on baseline regional selenium status.
In northern China, where soil selenium levels are naturally low, participants with the highest selenium intake had significantly lower hypertension risk—approximately 15-18% reduction compared to those with the lowest intake. This protective effect showed a clear dose-response relationship, with higher intake correlating with greater protection.
Conversely, in southern China with adequate soil selenium, no such protective relationship existed. In some high-intake southern subgroups, there was even a trend toward increased hypertension risk, suggesting the possibility of a U-shaped relationship where both deficiency and excess might be problematic.
Understanding how selenium research is conducted helps appreciate the robustness of these findings:
Detailed interview to assess all food and beverages consumed in the previous 24 hours
Reference data linking specific foods to their nutrient content, including selenium
Highly sensitive technique to measure selenium concentrations in biological samples
Standardized devices for accurate blood pressure measurement
Statistical methods to account for confounding factors
Long-term follow-up of participants to track health outcomes
The CHNS findings carry important implications for both public health policy and individual dietary choices:
The research suggests that regional selenium status should guide nutritional recommendations. Selenium supplementation programs would likely benefit populations in documented deficiency zones but might offer little advantage—or potential harm—in regions with adequate selenium.
In China, this means different dietary guidance might be appropriate for northern versus southern residents. Similar regional approaches could be valuable in other large countries with varying soil selenium levels.
For most people, the study reinforces the importance of obtaining nutrients primarily through a balanced diet rather than supplements. Unless you live in a known selenium-deficient region and have confirmed low intake, selenium supplementation is unlikely to benefit your blood pressure and could potentially be harmful in excessive amounts.
The research also highlights how individual nutritional needs can vary based on geographic location and local food systems—a concept often overlooked in blanket dietary recommendations.
The 20-year Chinese cohort study represents a significant advance in our understanding of selenium's relationship with hypertension. By revealing the crucial importance of regional background levels, the research helps explain previous contradictory findings and provides a more nuanced perspective on this essential nutrient.
The key takeaway is that selenium appears to follow a Goldilocks principle—too little increases hypertension risk in deficient populations, but more is not necessarily better for those with adequate status. As with many aspects of nutrition, balance and context matter profoundly.
The selenium-hypertension connection demonstrates that in nutrition, context is everything—the same substance can be medicinal, neutral, or potentially harmful depending on your starting point and environment.