VOLUME 8 NUMBER 3 • SEPTEMBER 2011
107
SA JOURNAL OF DIABETES & VASCULAR DISEASE
REVIEW
ruled out any influence of changes in body weight associated with
metformin therapy on TSH levels.
2
Our study also confirms these
findings.
Enhancement of inhibitory feedback of thyroid hormones on
TSH secretion is another mechanism suggested by Cappelli
et al
.
2
Induced constituent activation of the TSH receptor and increased
dopaminergic tone has also had been suggested by Vigersky
et
al
.
4
Previous studies have suggested that there is a disruption of
the neuroendocrine mechanisms in women with PCOS, mainly
due to a deficiency in hypothalamic dopamine.
5
Metformin
administration improves endogenous hypothalamic dopaminergic
tone, simultaneously with decreasing the insulin resistance in obese
PCOS patients.
6
The possibility that metformin administration
decreases TSH levels by increasing dopamine in the hypothalamus
may be the best explanation but needs to be fully elucidated by
further studies.
The main limitation of our study was the small number of
patients. However, a significant decrease in TSH levels was observed
in our patients.
Conclusion
In overweight PCOS patients with primary hypothyroidism,
treatment with metformin resulted in a significant fall in TSH and
in some cases improvement of hypothyroidism. We can begin
treatment of obese PCOS patients with subclinical hypothyroidism
with metformin and re-evaluate their thyroid function after six
months.
Funding
This research received no specific grant from any funding agency in
the public, commercial, or not-for-profit sectors.
Conflict of interest statement
The authors declare that they have no conflicts of interest.
Acknowledgements
This study was performed with the support of Mashhad Endocrine
Research Center. All authors have contributed significantly and are
in agreement with the content of the manuscript.
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