Normal Thyroid Hormone Levels Linked to Higher Sperm Counts in German Fertility Clinic Study

Men whose thyroid stimulating hormone falls within the standard laboratory reference range appear to have significantly higher sperm counts than men whose levels sit outside it, according to a retrospective study of 346 men conducted at a reproductive medicine center in Göttingen, Germany. The finding, published in Basic and Clinical Andrology, adds a piece of evidence to a long-standing and stubbornly contradictory debate: whether routine thyroid testing belongs in the andrology laboratory at all.

Thyroid function has been studied extensively in women seeking fertility treatment, but men have rarely been investigated, the authors note. Thyroid hormone receptors are expressed in the human testis, where they modulate the functioning of Sertoli and Leydig cells, and the role of thyroid hormones in testicular physiology before and during puberty is well established. What remains unclear is how much the thyroid matters for the adult testis and for semen quality. Clinical practice guidelines for assisted reproductive technology worldwide do not recommend routine screening for asymptomatic thyroid dysfunction, and thyroid evaluation is generally reserved for men presenting with ejaculatory or erectile dysfunction.

The research team, led by Alireza Alizadeh Moghadam Masouleh and colleagues, examined all men referred for the first time to the andrology laboratory at gyn-medicum in Göttingen between 2021 and 2023 for semen analysis as part of routine diagnostic workup or pre-ART examination. Men with azoospermia, genital infections, hormone supplementation, or heavy medical treatments such as radiotherapy or chemotherapy were excluded. The final cohort comprised 346 fertile and infertile men. Each participant provided a brief questionnaire covering age, smoking habits, and alcohol intake, and a single non-fasting blood sample was drawn on the same day as semen collection to measure TSH, FSH, LH, prolactin, testosterone, and the LH-to-testosterone ratio.

The cohort was relatively young, with a mean age of 35.8 years and a mean body mass index of 27.1 kilograms per square meter. Thirty-seven percent of participants reported being smokers. Alcohol consumption was low to moderate: three percent drank daily, 35 percent weekly, 44 percent monthly, and 17 percent not at all. By body weight classification, 37 percent were normal weight, 37 percent overweight, and 26 percent obese. Semen samples were collected after two to five days of abstinence and analyzed according to World Health Organization 2021 guidelines, with sperm concentration and motility assessed by two expert embryologists under quality control certification from the German Society of Andrology.

Of the 309 men for whom TSH values were recorded, using a normal range of 0.4 to 4 milli-international units per liter, 95 percent fell within the reference interval. Only one percent were below it and four percent above it. Two subjects had clearly low TSH levels of 0.01 milli-international units per liter, and one subject had a clearly elevated value of 8.6. Notably, TSH levels were not significantly affected by age, body mass index, smoking, alcohol consumption, or season, factors the authors deliberately included in their models because they are known confounders of thyroid function.

Among the various sex hormones evaluated, only one significant correlation emerged: a positive association between TSH and prolactin, with a Spearman coefficient of 0.199 and a p-value of 0.0001. A tendency toward a negative correlation between TSH and LH was suggested but did not reach statistical significance. The central result came from multivariate logistic regression, in which semen parameters were dichotomized according to WHO reference values and regressed on TSH levels while adjusting for age, body mass index, smoking, alcohol consumption, and season. When TSH values were within the normal range, sperm counts were significantly higher, with an odds ratio of 1.302, a p-value of 0.043, and a 95 percent confidence interval of 1.009 to 1.681. Age, unsurprisingly, influenced sperm count, concentration, and both total and progressive motility.

The authors also report that sperm concentration and motility were increased in men with normal TSH levels, although these differences did not reach statistical significance, and that among the few participants with above-normal TSH values, the frequency of abnormal sperm parameters, including count, total motility, and progressive motility, was higher. Because the study was retrospective, the team emphasizes that no causal relationship can be established. The number of men with abnormal TSH levels was small, which limits the statistical power of subgroup analyses, and the single-center design may restrict generalizability.

The new data land in a field crowded with conflicting results. Meeker and colleagues reported in 2007 that TSH levels were not associated with semen parameters in a large cohort of US men, and subsequent studies in men diagnosed with hypothyroidism, as well as Italian and Greek reports, similarly found no association. On the other side of the ledger, a Pakistani study found that each 1 milli-international unit per liter increase in serum TSH was accompanied by a decrease in sperm count of 5.9 million per milliliter and a 2.7 percent decrease in sperm motility, and researchers in India reported inverse correlations between TSH and semen volume, sperm motility, and sperm morphology in infertile men. A 2016 Italian study found that 7.4 percent of males from infertile couples had subclinical hypothyroidism and 3.7 percent subclinical hyperthyroidism, slightly above general population frequencies, and a recent meta-analysis pointed to adverse effects of subclinical hypothyroidism on sperm quality parameters. In China, a retrospective study of 8,478 men consulting for fertility problems found that in non-azoospermic men, high levels of free T3 were associated with better sperm motility, findings the German authors say confirm their own results.

The prevalence context matters for interpreting the Göttingen numbers. Thyroid dysfunction affects roughly one percent of the general population in the form of hyperthyroidism and six percent as hypothyroidism, and population-based studies place the prevalence of thyroid disorders between two and six percent worldwide, peaking at 6.6 percent among European and American adults. In Germany specifically, the age-standardized prevalence of at least one TSH measurement per 1,000 men rose from 165 in 2008 to 238 in 2017, levothyroxine was among the five most frequently prescribed drugs in Germany in 2021, and one cited report estimates that undiagnosed thyroid disorders, whether morphological or functional, may be found in up to 75 percent of the adult German population. Against that backdrop, the finding that only five percent of men in this fertility clinic cohort had abnormal TSH values is itself informative.

The authors conclude that male patients with abnormal TSH levels are not very common in their region, but they argue that TSH assessment in infertile couples should be routine in both partners, given the recorded worldwide increase in thyroid dysfunction and iodine deficiency. They call for further studies on thyroid testing in the andrology laboratory, noting that future work should account for iodine and selenium levels, which depend heavily on geographical location. The study’s limitations temper the message: thyroid function was assessed using TSH alone, since T3 and T4 measurements were not consistently available, preventing the researchers from distinguishing subclinical from overt thyroid dysfunction. Sperm morphology was not included because of incomplete and non-standardized data, and interobserver variability in semen assessment was not formally quantified. Larger prospective studies including a full thyroid profile and standardized semen analysis, the team writes, are needed to confirm these findings and clarify the role of thyroid function in male fertility.

Subject of Research: The association between thyroid stimulating hormone levels and semen parameters in men attending a German fertility clinic

Article Title: Thyroid stimulating hormone (TSH): does it live up to its promises in the andrology laboratory?

Article References: Alizadeh Moghadam Masouleh, A., Tobler, M., Atrabi, M. J., Vesali, S., Hosseini, R., Drevet, J., & Schmutzler, A. G. (2026). Thyroid stimulating hormone (TSH): does it live up to its promises in the andrology laboratory?. Basic and Clinical Andrology, 36(1), Article 21. https://doi.org/10.1186/s12610-026-00315-3

Image Credits: AI Generated

DOI: 10.1186/s12610-026-00315-3

Keywords: TSH, thyroid function, male infertility, sperm count, semen parameters, andrology, reproductive medicine, hypothyroidism, logistic regression, Göttingen, thyroid dysfunction, fertility clinic