What is The Impact of Excessive Iodine and Semen Quality in Fertile Men of China: An Association Study

Background: Iodine is an essential element for hormones synthesized by the human thyroid gland. Thyroid hormone deciency affects all body tissues, including multiple endocrine changes that alter growth hormones, corticotrophin, glucocorticoids, and gonadal function. In many countries, subfertility is an important problem affecting about 10–15% of all couples trying to conceive. Male subfertile factors have accounted for 25–30% of all cases in their studies. The aim of this study was to study the correlation between urinary iodine concentration (UIC) and semen quality of fertile male in China. Methods: semen and urine samples were collected from males who attended a survey for the reproductive physiological constants of male and female in China. All participants were fertile and they should be free from diseases of male reproductive system and thyroid related diseases. We studied the correlation between UIC and semen quality parameters in fertile males and the effect of iodine concentration on male reproduction. Participants were divided into six groups based on UIC. We measured semen parameters and UIC. Semen parameters or time-to-pregnancy (TTP) were analyzed by Spearman correlation, linear regression and multivariable logistic regression. Results: 1089 men were recruited in the study. The mean and median age of participants were 27.46±0.12 and 27±3.88 years, respectively. UIC of 274 (25.16%) men was lower than the UIC of WHO recommended. UIC of 405 men located in the region of WHO recommended. 62.35% of them were not located in the optimal region. Semen concentration and total sperm count were found to decrease when UIC increases when the UIC ≥ 100 ug/L. Conclusions: A male with decient UIC or excessive UIC has more risk of lower semen quality such as sperm concentration and total sperm count. In addition, if a male with decient UIC or excessive UIC, his wife has longer TTP than the males who had normal UIC. Decient UIC associated with lower semen quality and TTP than excessive UIC.

Each participant underwent a physical examination on the day of semen collection. Volunteers provided their semen samples as instructed by clinicians in a private room near the laboratory. Samples were collected in a wide-mouthed clean and clear plastic container. We analyzed semen samples within the rst hour after collection and assessed semen quality according to the criteria of the World Health Organization (WHO) standardized methods. We analyzed the pH, volume, density, total sperm count, spermatozoa with progressive and nonprogressive motility, immobile spermatozoa, and total motile sperm count following the guidance of the WHO (World Health Organization, 2010). In addition, two professional physicians veri ed and con rmed all sperm motility analyses using videos after on-site analysis.

Laboratory determinations
At least 20 ml urinary samples were collected on-site and frozen at −20°C until laboratory analysis. We measured all urinary samples using the same batch of kits. We measured UIC using a modi cation method based on Sandell-Kolthoff reaction (Pino et al., 1996).
Chi-square tests were used to compare categorical variables. The differences between the three UIC groups and the various sperm parameters were compared according to the Kruskal-Wallis test. We conducted linear regression (when the outcome was continuous) or multivariable logistic regression (when the outcome was dichotomous) to assess the association between UIC categories and semen parameters or TTP using random intercept models (Michael L, 2014) [22] . All regression models were adjusted for the following confound factors: age, body mass index (BMI), period of abstinence, alcohol consumption, smoking status, and education level. We considered con dence intervals that excluded one-or two-tailed P-values of <0.05 to be statistically signi cant. We performed all statistical analyses using the SPSS 19 software package (SPSS, Inc., Chicago, IL, USA).

Characteristics of participants
The general characteristics of 1089 men are provided in Table 1. UIC of 274 (25.16%) men was lower than the optimal UIC of WHO recommended. UIC of 405 men were higher than the optimal UIC of WHO recommended. 62.35% of them were not located in the optimal region.

Reproductive relative parameters and semen parameters
Reproductive relative and semen parameters of 1089 subjects are showed according to UIC grouping in Table 2. The wives of all the participants are being pregnancy. About 7% has more than 3 pregnant history 22.3% participants have more than one child. 5.1% couples have more than 12 months TTP. The sperm concentration (95.8%) and total sperm count (94.7%) were located in normal regions according to the WHO standard. 855 (78.51) samples had all normal semen parameters in 1089 participants.

Association between higher UIC and semen parameters
We found a linear association between excessive UIC and an increased incidence of low semen concentration (<15 M/ml) and low total sperm count (<39 M) (see Table 3, 4).
After unadjusted and adjusted multivariable logistic analyses, the relative risk for excessive UIC with abnormal parameters was signi cant in semen concentration and total sperm count. Men with excessive UIC had 18.53 times higher odds of having a low semen concentration (95% CI 4.20-81.73). When a man had excessive UIC, he had an 8.64 times higher odds of also having a low total sperm count (95% CI 3.07-24.34). In semen pH, however, excessive UIC was a protective factor (95% CI 0.48-0.98). If a man had excessive UIC, he had a more normal semen pH than other men (see Table 5).

Association between higher UIC and TTP
The average and median TTP were 4.569 and 3 months, respectively. TTP range was from 1 to 36 months. TTP increased with UIC, the unadjusted and adjusted regression coe cients were r = 0.251 (P = 0.000) and r = 0.253 (P =0 .000), respectively. According to logistical analyses, when a male had excessive UIC, his wife had 7.49 times higher risk of longer TTP (95% CI 3.34-16.80; 95% CI 3.37-16.00) in unadjusted and adjusted models, respectively (see Table 3 -5).

Association between de ciency UIC and semen parameters
We found a linear association between de ciency UIC and an increased incidence of low semen concentration (<15 M/ml) and low total sperm count (<39 M; see Table 6, 7).
After unadjusted and adjusted multivariable logistic analyses, the relative risk for de cient UIC with abnormal parameters was signi cant in semen concentration and total sperm count (see Table 7). This trend was depended on the UIC. The lower UIC associated with more risk for decreased semen quality once UIC was de ciency. When the UIC was severe, moderate, or mild de ciency, men had 22.84 (95% CI 1.86-269.95), 18.66 (95% CI 3.35-98.54) and 19.40 (95% CI 4.46-84.45) times higher odds of having a lower semen concentration than 15×106/ml. When a man had severe, moderate, or mild de cient UIC, he had 20.00 (95% CI 3.36-118.94), 9.06 (95% CI 2.67-30.70) and 9.13 (95% CI 3.39-24.55) times higher odds of having a lower total sperm count than 39×10 6 (see Table 8).

Association between de cient UIC and TTP
The average and median TTP were 5.367±4.97 and 3 months, respectively. TTP range was from 1 to 55 months. TTP decreased with UIC, the unadjusted and adjusted regression coe cients were r = 0.299 (P = 0.000) and r = 0.327 (P =0 .000), respectively. According to logistical analyses, When a man had severe, moderate, or mild de cient UIC, his wife had 16.93 (95% CI 3.81-75.19), 11.63 (95% CI 4.63-26.89) and 8.67 (95% CI 4.23-17.89) times higher risk of longer TTP in unadjusted models. The same trend was also showed in adjusted models (see Table 6-8).

Discussion
Public health problems induced by excess iodine are now emerging in many iodine-su cient regions (Partal-Lorente et al., 2017). In this study, we investigated the association between UIC and semen parameters for normal fertile men in Han, China. The study showed a relationship between de cient or excessive UIC and low semen concentration and total sperm count in semen parameters. When UIC was in de cient or excess, men had a higher incidence of low semen concentration and low total sperm count.
Few studies have reported the association between iodine and semen quality, especially in fertile populations. In 1992, it was reported that semen quality had declined gradually over the past 50 years (Carlsen et al., 1992). Swan reanalyzed data from 61 studies and used multiple linear regression and nonlinear models, which supported a signi cant decline in semen density. As a result, an environmental factor was deemed to be clearly warranted in addition to regional and temporal differences ( States began to change between 1965 and 1969. Similar results were found in Paris, France, and in Britain. In Toulouse, France, however, no sperm count alteration was exhibited. Toulouse faces the Mediterranean Sea, and adequate iodine intake was obtained from seafood. Similarly, because of the habit of eating seafood, sperm count had not altered in the past year in Japan. Based on these studies, this sperm count trend appeared to be consistent with iodine supplementation (Sakamoto et al., 2004). In 2017, adequate iodine intake associated with semen quality in men was proven by Partal-Lorente et al (Partal-Lorente et al., 2017). In this study, men with high semen iodine levels had more morphological sperm. Men with higher urinary iodine levels had lower motile sperm count. The participants came from 96 couples consulting for infertility at the Assisted Reproduction Unit of the hospital.
In another study, UIC was the prime indicator of iodine status in a population and was used to assess the nature and timeliness of salt iodization (Rohner et al., 2014). Our study focused on the association between excessive UIC and semen quality. We used UIC an indicator to analyze the association of semen quality of fertile men in China. Our study had some differences from other studies. The participants were proved fertile because their partners were pregnant.
They all were Hans and came from different regions of China. UIC has been associated with semen concentration and total sperm count in different statistical models. We did not determine total sperm count to be an independent semen parameter because it was the calculated product of semen concentration and semen volume. Excessive UIC posed greater risk with a lower semen concentration and lower total sperm count. According to research, the possible effect of excess iodine on spermatozoa was lower in humans than in animals. Some animal studies might explain the harmful effects of excessive iodine on sperm parameters. Oxidative stress was a proven male factor for subfertility because of its damaged semen quality (Ebisch et al., 2008). Increased oxidative stress could be generated after excess iodine intake (Chakraborty et al., 2016). In a rat study, excess iodine intake increased reactive oxygen species. As a result, iodine affected male fertility potentially by initiating apoptosis in spermatozoal cells (Mahapatra and Chandra, 2017).
This study had three limitations. First, we analyzed only one semen sample from each volunteer. Considering the study was investigated in a normal fertile population, one sample was suitable to assess semen quality in an epidemiological study (Stokes-Riner et al., 2007). Second, we randomly collected urinary samples on-site. Third, some important semen parameters, such as sperm DNA fragmentation, could not be analyzed because of poor laboratory conditions in some investigation elds. Forth, some CIs were wide, re ecting small sample sizes for select variables.

Conclusion
In this study, we associated de cient or excessive UIC with harmful effects on semen quality, which affected the TTP in the fertile male in China. Many studies have focused on the clinical manifestation of thyroid hormone de ciency, whereas few studies have shown that excessive iodine intake is related to male reproduction. Our results indicated that iodine may play a role in semen quality or male reproduction. Men with de cient or excessive UIC are associated with low semen density and low total sperm count. De cient or excessive UIC associated with lower semen quality and TTP than excessive UIC. This pro le requires additional studies to fully explain the role iodine may play in male reproduction. The study was approved by the Ethics Committee of the National Research Institute for Family Planning. All participants were informed about this study and signed consent forms before completing the questionnaire, agreeing to donate the sample of semen and a random sample of midstream specimen of urine the use in the current scienti c research.

Consent for publication
Not applicable.

Availability of data and materials
The datasets analyzed is available from the corresponding author on reasonable request.

Competing interests
The authors do not have any con icts of interest to declare. Authors' contributions NW and SCZ conducted the data analyses and manuscript writing; NW and FL designed the study and the outline of the manuscript; SCZ designed the questionnaire, GY and SMW collected the data. All authors read and approved the nal manuscript. UIC group: SD: severe de ciency( 20 ug/L), MOD: moderate de ciency(≥20 50 ug/L), MID: mild de ciency(≥50 100 ug/L), OREF: optimal(≥100 200 ug/L), MTA: more than adequate(≥200 300 ug/L), PE: possible excess(≥300ug/L)   Semen parameters was dichotomized per WHO standard. Multivariable logistic regression was performed for estimating ORs. Model 1 was cruded model and model 2 adjusted for age, education level, smoke status, alcohol status, BMI and residence. OREF: optimal(≥100 200 ug/L), MTA: more than adequate(≥200 300 ug/L), PE: possible excess(≥300ug/L)