Thyroid hormones play an important role in cell differentiation, growth, and metabolism. Several investigators have documented the role of thyroid hormones in the development of prostate cancer. However, to date there are only limited data available regarding thyroid hormone levels in benign prostatic hyperplasia (BPH).

A total of 5708 men aged 40 to 59 years who had participated in a health examination were included in the study. Lower urinary tract symptoms (LUTS)/BPH were assessed by international prostate symptom score (IPSS), prostate volume, maximal flow rate (Qmax), and a full metabolic workup. Serum levels of thyroid-stimulating hormone (TSH) and free thyroxine (T4) were measured using chemiluminescence immunoassay by commercial kits. We divided participants into quartiles based on their TSH and free T4 levels: first quartile, Q1; second quartile, Q2; third quartile, Q3; and fourth quartile, Q4. We then investigated their relationship using the chi-squared test, the Cochran-Armitage trend test, logistic regression analyses, and a propensity score matched case-control study.

The mean age of the study group was 51.1 ± 5.2 years, and the mean free T4 and median TSH were 1.05 ± 0.14 and 1.44 (0.96–2.13)ng/mL, respectively. In addition, the ratio of metabolic syndrome and low testosterone (<3.5 ng/mL) were 41.9% and 11.8%, respectively. There was a significant increase in the percentage of men with IPSS>7, Qmax<10 mL/sec, and  prostate volume ≥30 mL, with increase of free T4 quartile (IPSS>7(%): Q1:57.2, Q2:56.7, Q3:60.3, Q4:62.5, P=.001; Qmax<10 mL/sec(%): Q1:3.5, Q2:3.2, Q3:4.1, Q4:4.8, P=.038; total prostate volume ≥30 mL(%): Q1:15.2, Q2:16.4, Q3:18.0, Q4:19.3, P=.002). After adjusting for age, body mass index, testosterone, and metabolic syndrome, the odds ratio for prostate volume ≥30 mL of free T4 Q3 and free T4 Q4 were significantly higher than free T4 Q1 [odds ratio; 5-95 percentile interval), P value; Q1:.000 (references); Q2:1.140(.911-1.361), P=.291; Q3:1.260 (1.030-1.541), P=.025; Q4:1.367(1.122-1.665), P=.002]. After adjusting for age, body mass index, testosterone, metabolic syndrome, and prostate volume, the odds ratio for IPSS>7 of free T4 Q4 were significantly higher than that of free T4 Q1 (odds ratio (5-95 percentile interval), P value; Q1:.000 (references); Q2:.969 (.836-1.123), P=.677; Q3:1.123 (.965-1.308), P=.133; Q4:1.221 (1.049-1.420), P=.010). However, the odds ratio for Qmax<10 mL/sec was not significantly different between free T4 quartile groups after adjusting confounding factors. In propensity score matched analysis (matched for age, metabolic syndrome, testosterone, and body mass index at a 1:1 ratio), 1362 cases (Q4 of free T4) and 1362 control subjects (Q1, Q2, and Q3 of free T4) were included for comparison. The ratio of prostate volume ≥30 mL (15.1% vs. 19.3%, P = .004) and mean prostate volume (23.7±6.7 vs. 24.6±7.3 mL, P=.001) was higher in the case group than in the control group. Qmax and IPSS were not different between case and control groups. TSH was not significantly related to IPSS, Qmax, and total prostate volume in univariate and multivariate analyses.

Prostate volume, IPSS, and Qmax are significantly related to free T4, and prostate volume is significantly and independently related to free T4 in this study.

We found a potential role of thyroid hormone in developing BPH.