Brazil Nuts and Thyroid Support
Brazil nuts are not recommended as a routine supplement for thyroid support in adults taking levothyroxine, as there is insufficient evidence to support selenium supplementation for preventing or treating hypothyroidism in any population. 1
The Evidence on Selenium and Thyroid Function
The 2012 AACE/ATA clinical practice guidelines explicitly state that despite selenium's theoretical potential for beneficial effects on hypothyroidism and thyroid autoimmunity, "there are simply not enough outcome data to suggest a role at the present time for routine selenium use to prevent or treat hypothyroidism in any population." 1
What the Research Shows:
Mixed results from clinical trials:
- A European trial of 2,143 euthyroid women found that 200 µg/day selenomethionine reduced autoimmune thyroid disease, postpartum thyroiditis, and hypothyroidism 1
- However, a UK trial of 501 patients over age 60 found that varying selenium doses (100-300 µg/day) for 6 months showed no beneficial changes in T4 to T3 conversion 1
- A meta-analysis in Hashimoto's thyroiditis patients on levothyroxine found selenium decreased anti-TPO antibodies and improved mood, but caused no significant changes in levothyroxine dosing requirements 1
Important safety concern: One follow-up study found selenium supplementation was associated with an increased risk of diabetes 1
Specific Concerns About Brazil Nuts
Selenium Toxicity Risk
Brazil nuts contain extremely variable selenium content (2.7-11 µg Se/g), with each nut weighing 3-4g 2. This means a single Brazil nut can contain 8-44 µg of selenium—making it easy to exceed safe limits with just 2-3 nuts daily. The consumption of Brazil nuts "can increase the likelihood of Se toxicity, regardless of the quantity of the nuts consumed" 2.
Additional Health Risks:
- Aflatoxin contamination (external infection of nuts) 2, 3
- Allergic reactions in sensitive individuals 2, 3
- Radioactivity concerns 3
- Weight gain potential 3
- Se-induced type 2 diabetes mellitus 3
Critical Interaction with Levothyroxine
Timing is crucial if any food supplement is consumed. Levothyroxine should be taken 30-60 minutes before breakfast on an empty stomach for optimal absorption 1, 4. The FDA label explicitly states to "administer levothyroxine sodium tablets at least 4 hours before or after drugs known to interfere with levothyroxine sodium absorption" and to "evaluate the need for dosage adjustments when regularly administering within one hour of certain foods" 4.
Clinical Bottom Line
For adults on levothyroxine:
- Continue prescribed levothyroxine therapy as directed
- Take levothyroxine 30-60 minutes before breakfast with water 1, 4
- Monitor TSH every 6-8 weeks after dose changes, then every 6-12 months when stable 4
- Do not add Brazil nuts or selenium supplements without clear medical indication, as they provide no proven benefit for thyroid hormone dosing or clinical outcomes in hypothyroid patients on levothyroxine 1
Common Pitfall to Avoid:
Many "thyroid support" supplements marketed to patients may contain undisclosed thyroid hormone (9 out of 10 studied contained >91 µg/day levothyroxine and/or >10 µg/day triiodothyronine) 1. Physicians should specifically ask patients about all supplements, particularly those marketed as "thyroid support."
The focus should remain on optimizing levothyroxine dosing based on TSH monitoring, ensuring proper medication timing, and addressing any absorption issues—not on adding unproven nutritional supplements like Brazil nuts.