Thyroid health and anemia are linked in a large study of adults
☕ Includes a question for the family ↓
Thyroid healthPart of a story we are following · 2 articles · See every update
If you feel tired a lot, your thyroid health may be part of the story. A large study found that your thyroid and your blood are connected. People with higher levels of the main thyroid hormone were less likely to have anemia.
Anemia means your blood has too few red blood cells or too little hemoglobin, the part that carries oxygen. It can leave you tired and short of breath. The thyroid is a small gland in your neck. Its hormones help set how your body uses energy, including in the bone marrow, where red blood cells are made.
How the study worked
Researchers looked at 13,247 adults from a long-running Brazilian health study. The adults were civil servants, active or retired, ages 35 to 74, in six Brazilian locations. They were examined between 2008 and 2010. The team checked two thyroid measures and compared them with anemia. The results were published Sept. 28, 2026, in the Revista da Associação Médica Brasileira. The study looked at everyone at one point in time, so it shows a link, not which one comes first.
What they found
The two thyroid measures were free thyroxine and TSH. Free thyroxine is the main hormone your thyroid releases into the blood. TSH is the signal your brain sends to tell the thyroid to work.
People were sorted into five equal groups by free thyroxine level, from lowest to highest. Compared with the lowest group, the other four groups all had less anemia. The drop was biggest in the middle and upper groups. In the fourth group, the odds of anemia were about half those of the lowest group (an odds ratio of 0.49). The highest group was almost the same, at 0.52.
Here is how the groups compared with the lowest group:
| Free thyroxine group | Odds of anemia compared with the lowest group |
|---|---|
| Second | 0.80 |
| Third | 0.55 |
| Fourth | 0.49 |
| Fifth (highest) | 0.52 |
The pattern showed up in both women and men, with no differences between them. TSH, the brain’s signal, had no link to anemia.
What does this mean for you?
This study does not tell you to change anything on its own. It adds a useful piece to the picture. If tiredness or anemia has no clear cause, the thyroid is one more place worth a look. It also shows that thyroid hormone levels and red blood cells may be tied together more closely than many people think.
What you can do today
If you often feel tired and don’t know why, write down when it happens and bring the note to your next checkup. Ask whether a blood count and a thyroid test make sense for you. If you already take thyroid medicine, keep up with your regular blood checks.
Talk about it at home
Your thyroid is a small gland in your neck, and it works a bit like a dimmer switch for the energy in your body. Scientists looked at the health records of thousands of grown-ups and noticed that people with more of the thyroid’s main message in their blood tended to have healthier red blood cells, the tiny carriers that bring oxygen around the body.
Question for the table
The scientists only looked at everyone on one single day, like taking one photograph. How is a photograph different from a video, and what could a video show that a single picture cannot?
Keep exploring
Copies this article and its questions so you can paste them into ChatGPT, Claude, Gemini or the AI you use, and keep the conversation going.
Questions and answers
- What is free thyroxine?
- It is the main hormone your thyroid gland releases into the blood. A simple blood test can measure it.
- What did the study find about anemia?
- People with higher free thyroxine levels were less likely to have anemia. This held for both men and women.
- Was TSH linked to anemia?
- No. The study found no link between TSH levels and anemia.
- Does this mean I should get a thyroid test?
- Not by itself. If you have unexplained tiredness, ask your doctor whether a thyroid test and a blood count make sense.
