Researchers studied over 1,400 Chinese women over 45 to understand how selenium (a mineral found in foods) affects blood sugar control. They discovered that having too much selenium in the blood, especially a form called selenoprotein P, was linked to higher diabetes risk and worse blood sugar control. The study also found that inflammation in the body may explain why this happens. While selenium is important for health, this research suggests that more isn’t always better, and too much could be harmful for blood sugar management.

The Quick Take

  • What they studied: Whether having different amounts of selenium in the blood affects blood sugar control and diabetes risk in middle-aged and older women
  • Who participated: 1,430 Chinese women over 45 years old from a large national health survey conducted between 2015-2017
  • Key finding: Women with high levels of a selenium form called selenoprotein P had 48% higher risk of type 2 diabetes and worse blood sugar control markers compared to those with lower levels
  • What it means for you: If you’re a woman over 45, getting enough selenium is important, but excessive amounts from supplements or diet may harm your blood sugar control. Talk to your doctor before taking selenium supplements, especially if you’re concerned about diabetes risk.

The Research Details

This was a cross-sectional study, which means researchers took a snapshot in time of 1,430 women and measured their selenium levels and blood sugar markers all at once. They didn’t follow people over time, but rather looked at data collected during a large Chinese national health survey from 2015-2017. The researchers measured three different forms of selenium in the blood and compared them to several blood sugar measurements, including fasting blood glucose, insulin levels, and a marker called HbA1c that shows average blood sugar over three months. They also measured inflammation markers in the blood to understand how selenium might affect blood sugar through inflammation.

This study design is useful for finding patterns and associations between selenium levels and blood sugar problems. However, because it’s a snapshot rather than following people over time, we can’t prove that too much selenium actually causes blood sugar problems—only that they tend to occur together. The researchers also looked at inflammation as a possible explanation for why selenium might affect blood sugar, which helps us understand the mechanism.

The study used a large, nationally representative sample of Chinese women, which is a strength. The researchers measured multiple forms of selenium and multiple blood sugar markers, giving a more complete picture. However, this is a cross-sectional study, so it can’t prove cause-and-effect relationships. The study was conducted in China, so results may not apply equally to other populations. The researchers also calculated combined inflammation and oxidative stress scores, which is a sophisticated approach but requires careful interpretation.

What the Results Show

The main finding was that high levels of selenoprotein P (a specific form of selenium) were associated with a 48% higher risk of type 2 diabetes. Women with high selenoprotein P also had higher fasting blood glucose (the amount of sugar in blood after not eating), higher insulin levels, higher HbA1c (long-term blood sugar marker), and higher HOMA-IR (a measure of insulin resistance, meaning the body isn’t responding well to insulin). Regular plasma selenium was also linked to higher fasting blood glucose, higher insulin, and higher insulin resistance. A third form of selenium called GPx3 was only associated with higher fasting blood glucose. These associations were statistically significant, meaning they’re unlikely to be due to chance.

The researchers found that inflammation markers, particularly a substance called interleukin-6 (IL-6), partially explained the connection between selenium and blood sugar problems. This suggests that excessive selenium may harm blood sugar control partly by increasing inflammation in the body. The researchers created combined inflammation and oxidative stress scores to capture the overall inflammatory state, and these scores also showed mediation effects, meaning they helped explain why selenium affects blood sugar.

Previous research on selenium and blood sugar has been mixed and unclear. Some studies suggested selenium was protective, while others found it harmful. This study adds important evidence that too much selenium may be problematic, especially in middle-aged and older women. The finding that inflammation mediates this relationship is new and helps explain why previous studies may have found conflicting results—the effect of selenium on blood sugar may depend on whether it increases inflammation in a particular person.

This study is cross-sectional, so it shows associations but cannot prove that excess selenium causes blood sugar problems. The study only included Chinese women over 45, so results may not apply to men, younger women, or other ethnic groups. The researchers measured selenium and blood sugar at only one point in time, so we don’t know if these associations are stable or change over time. The study couldn’t account for all possible factors that might affect blood sugar, such as physical activity levels or detailed dietary information. Finally, the mediation analysis (showing inflammation as a link) is based on statistical modeling and needs confirmation in future studies.

The Bottom Line

Based on this research, women over 45 should aim to get adequate selenium from food sources (like Brazil nuts, fish, and eggs) rather than taking high-dose supplements without medical guidance. If you’re considering selenium supplementation, discuss it with your doctor first, especially if you have risk factors for diabetes or prediabetes. The recommended daily amount of selenium for adult women is 55 micrograms, and most people eating a varied diet get enough. This research suggests more is not better when it comes to selenium.

This research is most relevant to women over 45, particularly those with family history of diabetes, prediabetes, or metabolic concerns. Men and younger women should also be cautious about excessive selenium intake, though this study specifically examined older women. People taking selenium supplements should discuss their intake with their healthcare provider. Those with existing diabetes or blood sugar problems should be especially careful about selenium supplementation.

Blood sugar changes from selenium exposure likely develop gradually over months to years, not days or weeks. If you reduce excessive selenium intake, improvements in blood sugar markers would likely take several weeks to months to become apparent. Long-term monitoring through regular blood work is important for tracking changes.

Want to Apply This Research?

  • Track daily selenium intake from food sources and supplements (target: 55 micrograms for women). Log sources like Brazil nuts (1 nut = ~95 mcg), fish servings, and eggs. Compare weekly averages to recommended amounts.
  • If currently taking selenium supplements, work with your doctor to determine if supplementation is necessary. Replace high-dose supplements with food sources of selenium. Set a reminder to discuss selenium intake at your next doctor’s visit, especially if you have blood sugar concerns.
  • Schedule fasting blood glucose and HbA1c tests every 6-12 months if you have risk factors for diabetes. Track any changes in energy levels, thirst, or other diabetes symptoms. Monitor supplement intake monthly to ensure you’re not exceeding recommended amounts. Keep records of dietary selenium sources to identify if intake is excessive.

This research shows an association between high selenium levels and blood sugar problems in middle-aged Chinese women, but cannot prove that excess selenium causes diabetes. Results may not apply to all populations. This information is for educational purposes and should not replace professional medical advice. If you have concerns about your blood sugar, selenium intake, or diabetes risk, consult with your healthcare provider before making dietary changes or starting supplements. Anyone with existing diabetes or prediabetes should work with their doctor before adjusting selenium intake.