Study analysis · The Journal of nutrition · 2025
Too much selenium could be giving you diabetes — and you're probably taking it without knowing.
Eat 60 micrograms of selenium a day to stay healthy, but go over 255 and you might increase your risk of type 2 diabetes.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study looked at lots of other studies about how much selenium people in China need to stay healthy. It didn't test selenium itself—it just put together what others found. So we know selenium levels in the blood go up when people eat more, but we can't say for sure that eating more selenium makes you healthier or sicker.
What’s the bottom line?
Your body needs selenium to stay healthy, but too much can be harmful — this study figured out the perfect amounts for people in China.
How strong is this study?
This study did a good job collecting and combining many other studies, which is smart. But since the original studies weren't experiments where people were randomly assigned to eat different amounts of selenium, we can't be totally sure the results are because of selenium alone—maybe other things like diet or lifestyle played a role.
40 / 100
- COI disclosure+40/40
- Data availabilitydata not shared
- Code availabilitycode not shared
0 / 100
- Randomizationrandomization unclear
- Blindingblinding unclear
- Control groupno control group
- Sample sizeno sample size reported
- Follow-upno follow-up reported
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervals+15/15
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 547 / 100
Probability of being correct
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
This design cannot establish causation — the findings describe an association, not a cause. This is a systematic review and meta-analysis, but the primary studies included are not specified as randomized controlled trials. Since randomization, blinding, and control group details are unknown for the primary studies, they cannot be classified as RCTs. Therefore, the evidence level defaults to systematic review of observational studies (cohort), which cannot establish causation.
No Conflicts
No conflicts of interest identified
No conflicts of interest were declared, and the study was funded by a public health project with no indication of industry influence or author ties to commercial entities.
Funders
Conflict Details
Public Health Emergency Project Nutrition Health and Healthy Diet Campaign: Received funding for research
Public Health Emergency Project Nutrition Health and Healthy Diet Campaign: Received funding for research
Public Health Emergency Project Nutrition Health and Healthy Diet Campaign: Received funding for research
Public Health Emergency Project Nutrition Health and Healthy Diet Campaign: Received funding for research
The study relies on the SELECT trial for setting the tolerable upper intake level, but no industry funding or author affiliations with commercial entities were disclosed. All authors declared no conflicts of interest.
Key takeaways
- 01
50 micrograms a day fills your body’s selenium needs; 60 micrograms keeps almost everyone covered; more than 255 micrograms raises diabetes risk.
- 02
Yes — eating too much selenium (like from supplements) could make you more likely to get diabetes, while too little harms your immune system and thyroid.
Surprising findings
- The study used data from the SELECT trial — a U.S.-based cancer prevention study — to set dietary guidelines for Chinese adults.It’s unusual to extrapolate nutrient thresholds across such different populations with varying diets and soil selenium levels, yet the authors claim high confidence despite this mismatch.
- Infant selenium needs (15–20 mcg/day) were extrapolated from maternal intake and breast milk levels — not from direct infant trials.Most people assume infant guidelines are based on rigorous pediatric studies, but here they’re inferred from adult data — a major methodological gap.
Practical takeaways
Check your multivitamin label — if it contains more than 200 mcg of selenium, consider switching to one with 50–100 mcg or none at all if you eat Brazil nuts or seafood regularly.
This applies mainly to populations with moderate selenium intake; those in low-selenium regions (e.g., parts of China or Europe) may still benefit from supplementation.
high confidenceIf you take selenium supplements daily, track your total intake — including food (Brazil nuts = 544 mcg per ounce!) — and avoid exceeding 255 mcg/day.
The 255 mcg UL is for long-term daily intake; occasional spikes (e.g., from a single Brazil nut) are unlikely to cause harm.
high confidenceParents: Don’t give kids selenium supplements unless advised by a doctor — infant needs are easily met through breast milk or formula.
The infant AI values are extrapolated, not directly measured — so caution is warranted.
medium confidenceWhy this study matters
The Goldilocks Dose: 60 mcg is Just Right
The study found that 50 micrograms of selenium daily saturates selenoprotein P (SELENOP), the key biomarker for selenium status, while 60 micrograms ensures 97–98% of Chinese adults meet their needs. This is the target Recommended Nutrient Intake (RNI).
Most people think more supplements = better health, but this shows there’s a precise sweet spot — and going beyond it may backfire. Your multivitamin might already be pushing you past it.
The UL Drop: 400 → 255 mcg
The tolerable upper intake level (UL) for selenium was slashed from 400 to 255 micrograms per day based on data from the SELECT trial, which linked higher selenium intake to increased type 2 diabetes risk.
This isn’t just a tweak — it’s a 36% reduction in the safe limit. Many supplements still list 200–400 mcg as safe, making this a major red flag for consumers.
U-Shaped Danger Zone: Too Little OR Too Much
Selenium follows a U-shaped curve: deficiency harms thyroid and immune function, but excess intake above 255 mcg/day increases insulin resistance and diabetes risk — meaning both extremes are dangerous.
It flips the script on 'more is better' thinking. Selenium isn’t like vitamin C — it’s a tightrope walk, not a ladder to climb.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Your body needs selenium to stay healthy, but too much can be harmful — this study figured out the perfect amounts for people in China.
Research results
50 micrograms a day fills your body’s selenium needs; 60 micrograms keeps almost everyone covered; more than 255 micrograms raises diabetes risk.
What this means - more context
Yes — eating too much selenium (like from supplements) could make you more likely to get diabetes, while too little harms your immune system and thyroid.
This study establishes updated Dietary Reference Intakes (DRIs) for selenium for Chinese residents based on saturation of plasma selenoprotein P and adverse health effects from excess intake.
The study recommends a daily selenium intake of 50 μg to saturate SELENOP, 60 μg as the target RNI for adults, 15 μg/d for infants 0–6 months, and 20 μg/d for 7–12 months, while reducing the UL from 400 to 255 μg/d based on increased type 2 diabetes risk in the SELECT trial.
Methods Used
Derived from dose-response studies on SELENOP saturation in Chinese adults and analysis of the SELECT trial’s long-term, large-sample data on selenium intake and type 2 diabetes risk, with extrapolation from maternal intake to infant requirements.
Main Finding
A daily selenium intake of 50 μg saturates SELENOP; 60 μg is sufficient for 97–98% of Chinese adults; and the tolerable upper intake level should be reduced from 400 to 255 μg/d due to diabetes risk above this threshold.
Confidence Level
High — based on large, long-term RCT (SELECT), dose-response human studies, and consistent biomarker (SELENOP) data with clear saturation thresholds.
Study Flags
Red Flags
- •Relies on SELECT trial data from a U.S. population to set UL for Chinese adults
- •No new primary data collected — all recommendations extrapolated from prior studies
- •U-shaped risk model assumed without new dose-response validation in Chinese cohort
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Surprising Findings
The study used data from the SELECT trial — a U.S.-based cancer prevention study — to set dietary guidelines for Chinese adults.
It’s unusual to extrapolate nutrient thresholds across such different populations with varying diets and soil selenium levels, yet the authors claim high confidence despite this mismatch.
Practical Takeaways
Check your multivitamin label — if it contains more than 200 mcg of selenium, consider switching to one with 50–100 mcg or none at all if you eat Brazil nuts or seafood regularly.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 547 / 100
Probability of being correct
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
Human Meta-Analysis
Subject
Moderate probability
on the GRADE evidence scale
This study looked at lots of other studies about how much selenium people in China need to stay healthy. It didn't test selenium itself—it just put together what others found. So we know selenium levels in the blood go up when people eat more, but we can't say for sure that eating more selenium makes you healthier or sicker.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Comprehensive systematic review with meta-analysis of multiple studies
- Uses validated biomarkers (SELENOP, GPX3) to define nutritional requirements
- Incorporates large, well-conducted trials (SELECT) for upper intake level determination
Weaknesses
- Primary study designs are unknown and likely observational, limiting causal inference
- No explicit assessment of risk of bias across included studies
- Reliance on a single trial (SELECT) for UL recommendation without sensitivity analysis
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Your body needs selenium to stay healthy, but too much can be harmful — this study figured out the perfect amounts for people in China.
Research results
50 micrograms a day fills your body’s selenium needs; 60 micrograms keeps almost everyone covered; more than 255 micrograms raises diabetes risk.
What this means - more context
Yes — eating too much selenium (like from supplements) could make you more likely to get diabetes, while too little harms your immune system and thyroid.
This study establishes updated Dietary Reference Intakes (DRIs) for selenium for Chinese residents based on saturation of plasma selenoprotein P and adverse health effects from excess intake.
The study recommends a daily selenium intake of 50 μg to saturate SELENOP, 60 μg as the target RNI for adults, 15 μg/d for infants 0–6 months, and 20 μg/d for 7–12 months, while reducing the UL from 400 to 255 μg/d based on increased type 2 diabetes risk in the SELECT trial.
Methods Used
Derived from dose-response studies on SELENOP saturation in Chinese adults and analysis of the SELECT trial’s long-term, large-sample data on selenium intake and type 2 diabetes risk, with extrapolation from maternal intake to infant requirements.
Main Finding
A daily selenium intake of 50 μg saturates SELENOP; 60 μg is sufficient for 97–98% of Chinese adults; and the tolerable upper intake level should be reduced from 400 to 255 μg/d due to diabetes risk above this threshold.
Confidence Level
High — based on large, long-term RCT (SELECT), dose-response human studies, and consistent biomarker (SELENOP) data with clear saturation thresholds.
Study Flags
Red Flags
- •Relies on SELECT trial data from a U.S. population to set UL for Chinese adults
- •No new primary data collected — all recommendations extrapolated from prior studies
- •U-shaped risk model assumed without new dose-response validation in Chinese cohort
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Surprising Findings
The study used data from the SELECT trial — a U.S.-based cancer prevention study — to set dietary guidelines for Chinese adults.
It’s unusual to extrapolate nutrient thresholds across such different populations with varying diets and soil selenium levels, yet the authors claim high confidence despite this mismatch.
Practical Takeaways
Check your multivitamin label — if it contains more than 200 mcg of selenium, consider switching to one with 50–100 mcg or none at all if you eat Brazil nuts or seafood regularly.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 547 / 100
Probability of being correct
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
Human Meta-Analysis
Subject
Moderate probability
on the GRADE evidence scale
This study looked at lots of other studies about how much selenium people in China need to stay healthy. It didn't test selenium itself—it just put together what others found. So we know selenium levels in the blood go up when people eat more, but we can't say for sure that eating more selenium makes you healthier or sicker.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Comprehensive systematic review with meta-analysis of multiple studies
- Uses validated biomarkers (SELENOP, GPX3) to define nutritional requirements
- Incorporates large, well-conducted trials (SELECT) for upper intake level determination
Weaknesses
- Primary study designs are unknown and likely observational, limiting causal inference
- No explicit assessment of risk of bias across included studies
- Reliance on a single trial (SELECT) for UL recommendation without sensitivity analysis
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
This study did a good job collecting and combining many other studies, which is smart. But since the original studies weren't experiments where people were randomly assigned to eat different amounts of selenium, we can't be totally sure the results are because of selenium alone—maybe other things like diet or lifestyle played a role.
40 / 100
- COI disclosure+40/40
- Data availabilitydata not shared
- Code availabilitycode not shared
0 / 100
- Randomizationrandomization unclear
- Blindingblinding unclear
- Control groupno control group
- Sample sizeno sample size reported
- Follow-upno follow-up reported
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervals+15/15
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 547 / 100
Probability of being correct
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
This design cannot establish causation — the findings describe an association, not a cause. This is a systematic review and meta-analysis, but the primary studies included are not specified as randomized controlled trials. Since randomization, blinding, and control group details are unknown for the primary studies, they cannot be classified as RCTs. Therefore, the evidence level defaults to systematic review of observational studies (cohort), which cannot establish causation.
No Conflicts
No conflicts of interest identified
No conflicts of interest were declared, and the study was funded by a public health project with no indication of industry influence or author ties to commercial entities.
Funders
Conflict Details
Public Health Emergency Project Nutrition Health and Healthy Diet Campaign: Received funding for research
Public Health Emergency Project Nutrition Health and Healthy Diet Campaign: Received funding for research
Public Health Emergency Project Nutrition Health and Healthy Diet Campaign: Received funding for research
Public Health Emergency Project Nutrition Health and Healthy Diet Campaign: Received funding for research
The study relies on the SELECT trial for setting the tolerable upper intake level, but no industry funding or author affiliations with commercial entities were disclosed. All authors declared no conflicts of interest.
Standing
Who’s using this study?
The videos and claims on this site that lean on this study, and the researchers who wrote it.
1 video from Thomas DeLauer cite this study, drawing 1 claim from it.
- Strong evidence
At least some randomized or controlled trials support this claim.
Evidence
Authored by
4 researchersIf this is your work, this is how we attribute it on Fit Body Science. Feng Han is listed as the lead author.