Light And Hypothyroidism – Cure Or Cause?

This article takes a look at the effects of near infrared laser therapy on thyroid hormone levels. Red and near-infrared therapy at low doses can decrease hypothyroidism and the autoimmune response sometimes causing it. Here I am going to look at some animal studies showing positive and negative effects on thyroid hormone. It seems that more is not better.

Positive Studies Using Light To Increase Thyroid Hormones

There are many LLLT studies showing positive effects on thyroid hormones in animals and humans, some of which I will go into detail in future. This rabbit study is a good example and has some similarities to the negative studies discussed after.

This study takes five groups of eight New Zealand rabbits. Groups 2 to 5 had surgery to install a dental implant. Groups 3 to 5 were irradiated with light therapy of differing doses. Group one served as an absolute control – neither surgery nor light therapy. Group 2 was a control for light therapy –  surgery only.

The animals were male and weighed 3 to 4kg. The device used was a GaAlAs laser with a wavelength in the near infrared (830nm). Power output was 50 mW (not pulsed).

In the laser treated groups the animals received either 5 J/cm2, 10 J/cm2, or 20 J/cm2 per session. That dose was split and applied to both sides of the animal: for example in the 5 J/cm2  group it would have had 2.5J/cm2 per side, per session. 7 sessions total were applied with 48hrs between them. The implantation site was used as the site for laser treatment.


“While animals were still under general anesthesia, those in the experimental groups were shaved and tattooed with a surgical marker over the region corresponding to the long axis of the dental implant, creating a target for laser irradiation.

The location of thyroid gland in rabbits seems to be closer to the mouth/teeth than in humans. It is unclear if the radiation was directly on the thyroid gland – if not it was close.

The laser treatment time was 51 seconds, 101 seconds and 201 seconds in the 5, 10, and 20J/cm2 groups. It’s unclear if this was both sides or combined time. Laser treatment was started immediately after the dental implant and repeated every 48 hours for seven total sessions over 13 days.

Animals had blood drawn at four time points –

  1. Baseline.
  2. During laser treatment period.
  3. Also during laser treatment period.
  4. 72 hrs after the last laser treatment.

Have a look at the results in the table 2. While there are variations in hormones in the different time points it seems that the general pattern of thyroid hormones from laser therapy is positive and in agreement with the statement from the authors.

C1 and C2 received no laser treatment. E5, E10 and E20 received LLLT.

”We found significant differences in thyroid hormone levels after LLLT, from time points 1–4.”  

I think the most significant measurement here might be the T3 levels at time point 4 (72 hours after the last treatment) in the group which had received 10 J/cm2. This was the highest level of thyroid hormone (T3) of all the groups and time points.

Negative Results Using Light On Thyroid

This second study [*] used smaller female rabbits (1.75kg), about half the size of the male rabbits used in the previous study. After an adaptation period to the laboratory 20 rabbits were divided into two groups. One group was kept as a control group and the other received laser therapy.  There was no dental implant procedure in this experiment.

The medical laser device used in this experiment had the same infrared wavelength as in the previous experiment – 830nm. The power output was 150 mW – the  previous experiment was only 50mW. This might an important factor. Though there are other differences between positive and negative studies the 150mW/50mW discrepancy stands out to me. In all of the other studies that I have read  the positive results were achieved using 30-50mW (unless pulsed).

The authors tell us that they used a spot size of 8 mm the distance from 1 cm. The previous study did not give information on spot size and it can’t be inferred that given. It’s also not clear whether the laser device was 150 mW at 0cm or at 1cm. If they had measured the power of the device at the tip of the device as 150mW and then used the device at a 1 cm distance the power of treatment would have been lower than  150 mW (but almost certainly significantly higher than 50mW).


The treatment duration in this study was significantly longer than the previous study, it’s described as twice daily for 15 minutes continuously. Again the reporting is unclear. This could be 7.5 minutes each side total per day – or it could mean 60 minutes total on only one side per day –  or anything in between. The abstract provides further confusion, seeming to indicate 5 minutes per side per day. It’s another significant difference in dosing either way.

This study had three consecutive days of laser treatment compared to the previous study which had seven days of treatment with one day off between every treatment.

This study only started sampling blood for thyroid hormones after the last treatment. After treatment it was found that total T3 decreased significantly and gradually –  total T3 also decreased in the control group, though initial T3 figures (after laser treatments)  were lower in the laser treatment group and remained lower throughout the 30 day testing period.

The control group showed a clear increase in T3 from about day 22 – T3 continued to decline in the laser treated group. By day 30 T3 in laser group was 68 compared with 106 for the control group. It seems there is some other antithyroid factor affecting both groups – though there is a clear difference between groups, with the laser group worse off.


T4 levels also decreased in both groups. The T4 levels were initially lower in the laser treated group,  there was a greater decline in T4 levels in the later treated group. The test results from day 25 to day 30 indicate that T4 may have begun to correct and increase – it was still far below day one.

Unlike the previous report this paper examined thyroid stimulating hormone (TSH).  TSH generally goes in the opposite direction of the thyroid hormones. This pattern was found in this study. TSH was higher in the laser group at all points during the study. TSH increased in the laser group peaking at around day 10 and decreasing toward the control group by date 30.


(Some of the text boxes on the graphs are incorrectly labelled in the original paper –  look at the vertical text in the graph box rather than underneath to avoid confusion.)

The authors of the paper reported that the animals were behaving in a manner that support blood test results toward hypothyroidism.

“The female rabbits irritated with LPLT 830 nm showed disquiet, coldness, dullness, depression, impairment and fatigue, since no such symptoms observed in the control group.”

Because of the different animals used and the incomplete reporting (which is par for the course in LLLT papers) it’s impossible to say with certainty which factor is the cause of the negative results. As I said the 150mw power and extended treatment period stands out to me. It may be that the power is too high, or the time is too long, or both combined, or something else.

I’ll lastly point out further confusion in the reporting. Paper one doses 50mW for 51s, paper 2 doses 150mW for 150-1500s (?) and yet both achieve 5J/m2. Accurate time and spot size reporting are required for comparison.


This study used similar animals to study 2 [*]. The study does not report many of the laser treatment metrics, they are perhaps similar to study 2. It does report a dose of 4J/cm2. The results for T3, T4 and TSH are similar to the second study – indicating low level laser induced hypothyroidism.The authors note that this study shows that LLLT could be used to treat hyperthyroidism.

“Finally, our findings serve as proof-of-principle that laser therapy could be used in treatment of goiter, hyperthyroidism and other thyroid diseases.”

Treating Hyperthyroidism?

One final reference for LLLT induced hypothyroidism. [*]

“These findings revealed that exposing normal thyroid glands of healthy rabbits to laser irradiation in a mentioned dose and time induces a case of hypothyroidism in the animals lasting for a time depending on the dose and time of exposure.”

Light therapy can treat hypothyroidism, cure hyperthyroidism or create hypothyroidism. Dosing needs to be carefully approached to achieve appropriate results.