Both chronic pain and obesity are known to affect reproductive hormone profiles in male patients. However, the effect of these conditions, alone or in combination, on male fertility potential has received less attention. 20 chronic musculoskeletal pain patients and 20 healthy controls were divided into lean and overweight subgroups according to their BMI. Current level of chronic pain (visual analogue scale) and pressure pain thresholds (PPTs) in 16 predefined sites, classically described and tested as painful points on the lower body, were measured. Levels of reproductive hormone and lipid profiles were assessed by ELISA. Sperm concentration and motility parameters were analyzed using a computer-aided sperm analysis system. Sperm concentration, progressive motility, and percentage of hyperactivated sperm were generally lower in the chronic pain patients in both lean and overweight groups. The overweight control and the lean chronic pain groups demonstrated a significantly lower percentage of progressively motile sperm compared with the lean control group, suggesting that musculoskeletal chronic pain may have a negative influence on sperm quality in lean patients. However, due to the potential great negative influence of obesity on the sperm parameters, it is difficult to propose if musculoskeletal chronic pain also influenced sperm quality in overweight patients. Further research in chronic pain patients is required to test this hypothesis.
Male factor infertility accounts for approximately 40% of infertility cases [
The World Health Organization (WHO) defines overweight and obesity as excessive or abnormal fat accumulation, which impairs health [
In contrast to the extensive attention paid to the effect of obesity on many health-related issues, the impact of obesity on reproduction has received less attention [
The role of reproductive hormones in pain is not well understood. Many hormonal effects on pain which were initially thought to be due to gonadal release of the hormone may actually be due to the hormone synthesis in tissues such as the brain and spinal cord (e.g., progesterone and estradiol). Many of the central regions implicated in pain and analgesia contain receptors for both estrogens and androgens and have the ability to synthesize steroids locally. Binding of specific steroids to their receptors within these central and peripheral regions is likely involved in ligand-dependent transcriptional events, thereby influencing the expression of various neurotransmitters and receptors. It has been suggested that sex steroids have profound effects not only on developmental organization but also on the ongoing dynamics of the nervous system [
Musculoskeletal disorders (MSDs) are generally associated with pain due to a sensory disturbance, caused by proinflammatory conditions [
Neuroplasticity is the alteration of neural pathways and synapses due to changes in behavior, environment, and neural process as well as changes resulting from physical injury like obesity [
Obesity can affect chronic pain, and a link between obesity and semen quality exists. Considering that both obesity and chronic pain can affect the reproductive hormonal profiles in male patients, this study aimed to assess and compare reproductive hormones and semen quality in overweight and normal weight chronic pain patients and healthy controls to provide a deeper insight into the possible relation between obesity, chronic pain, and male fertility potential.
This study was performed at the orthopedics department, Aalborg University Hospital, and Fertility Clinic in Dronninglund, Denmark, from June 2014 to December 2015, following approval from the Scientific Ethics Committee of the Northern Jutland Region, Denmark (approval reference no. N-20140025).
Patients attending the orthopedics department of Aalborg University Hospital (Aalborg, Denmark), with a history of at least 3 months of low back pain and lower extremity chronic pain with a minimum score of three on the visual analogue scale (VAS), were considered and invited by the study healthcare professional to take part in this study as the test group. Healthy volunteers with no previous history of chronic musculoskeletal pain were also recruited from males visiting the clinic for checkups or as accompanying persons. Age (18–46 years) and BMI (lean < 25 kg/m2 < overweight) were initially considered to recruit a sufficient number of patients for all study groups.
All participants provided written consent and filled a questionnaire describing the history of the chronic pain and information regarding possible confounding factors (i.e., medication, reproductive surgery, or complications), which were taken into account for the patients’ inclusion and assessment of results. Based on the approved protocol, participants using medications including strong analgesics (e.g., opioids), having an ongoing infection, with current or previous neurologic, musculoskeletal, or mental illnesses, malignancy, drug addiction (cannabis, opioids, or other psycho drugs), reproductive surgery, and related complications were not included in the study.
Height and weight were measured to calculate the body mass index (BMI). A BMI ≥ 25 kg/m2 was considered as overweight in this study. Recruitment was continued until each of the chronic pain and control groups had equal numbers (10) of participants in the overweight and lean groups (determined based on BMI).
The subgroups (2 × 2 design) based on BMI and pain status (10 patients in each group) are as follows: Overweight patients with chronic pain (OP) Overweight patients without chronic pain (OC) Lean patients with chronic pain (LP) Lean patients without chronic pain (LC).
The mean (±SD) and median (min–max) age and BMI of the participants have been demonstrated in Table
The age and BMI (body mass index) of the participants in the study groups. Multivariate two-way analysis of variance (MANOVA) was used to compare differences in BMI and age.
Age (years) | BMI | |||
---|---|---|---|---|
Mean ± SD | Median (min, max) | Mean ± SD | Median (min, max) | |
OP | 30.8 ± 9.7 | 30 (18, 46) | 29.7 ± 5.2 | 27.9 (25.2, 41.4) |
OC | 26.1 ± 3.8 | 25 (22, 33) | 26.2 ± 1.5 | 25.6 (25.1, 29.8) |
LP | 27.6 ± 5.4 | 26 (19, 36) | 23.7 ± 1.3 | 24.4 (20.9, 24.7) |
LC | 25.9 ± 6.9 | 23 (19, 42) | 22.4 ± 0.5 | 22.4 (21.3, 22.9) |
BMI: body mass index (kg/m2); OP: overweight with chronic pain; OC: overweight control; LP: lean with chronic pain; LC: lean control (N = 10 per group).
Schematic timeline demonstrating the order procedures performed in the study.
The chronic pain patients were asked to rate their minimum and maximum pain intensity at rest condition during the previous three months, by marking on a 10 cm horizontal visual analogue scale (VAS) of 0–10 (0 = “no pain”; 10 = “the most pain imaginable”). The updated Short Form McGill Pain Questionnaire (SF-MPQ-2) [
Quantitative sensory testing paradigms such as pressure pain threshold (PPT) mapping by dynamic pressure algometry have been used to assess the functional status of the excitability of the pain system and to describe mechanical pain sensitivity in larger areas of the body covering one or more muscles [
The anatomic sites for pressure pain threshold evaluations over the muscles, patellar tendon, pes anserinus bursae, and supraspinous ligaments in the anterior, posterior, and lateral views. 1: vastus medialis muscle; 2: rectus femoris muscle; 3: vastus lateralis muscle; 4: adductor longus muscle; 5: tibialis anterior muscle; 6: peroneus longus muscle; 7: patellar tendon; 8: pes anserinus bursae; 9: popliteous muscle; 10: iliacus muscle; 11: quadrates lumborum muscle; 12: supraspinous ligaments, area between L5–S1 and S1–S2; 13, 14: extensor digitorum brevis; 15: extensor hallucis longus; 16: flexor halluces longus; C: deltoids.
A gradually increasing pressure was applied to the predefined points by the investigator, while subjects were instructed to press the stop button to record the PPT at “the point where the pressure sensation just becomes painful.” A display on the algometer aided the investigator to deliver a constant increasing pressure (30 kPa/s), with the algometer tip (1 cm2 probe area) applied perpendicularly at the stimulation site. The procedure was repeated three times with an interval of 1 min for all test points. Averages of the three repetitions were considered as the subject’s PPT for each test point and used for further analysis.
All participants were asked to fast for ≥12 hours prior to attending the assessment sessions. Blood samples from all participants were collected from the median cubital, cephalic, or basilic veins by an experienced technician at the laboratory of clinical biochemistry at Aalborg University Hospital (Aalborg, Denmark) and assessed for lipid profiles (triglyceride, total cholesterol, LDL, VLDL, and HDL), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) according to the routine protocols. Testosterone levels were analyzed and reported by the “Statens Serum Institut (SSI)” (Copenhagen, Denmark).
Semen samples were collected by masturbation and allowed to liquefy for 30–45 minutes at room temperature. Following liquefaction, the total volume of each sample was measured using a graduated pipette, before being divided into three parts to be used for the following assessments.
Five microliters of the liquefied sperm suspension was loaded into a “Leja chamber slide” (20
The SCA motility module provided detailed velocity and motion-path kinematic parameters. The default cutoff values of the SCA were used to assess the following motion parameters as also specified by the WHO (WHO [
The percentage of hyperactivated spermatozoa was assessed based on the VCL, LIN, and ALH parameters at 50 fps.
Air-dried sperm smears were prepared and stained using “Spermblue” (Microptic S/L, Barcelona, Spain) according to the manufacturer’s instructions (10 minutes in fixative solution followed by 10 minutes in sperm blue stain) before being assessed using the morphology module of the SCA (automatically quantified measurements of sperm head and midpiece) at 1000x magnification.
The DNA fragmentation of the samples was assessed using the Halosperm kit (Halotech, Madrid, Spain) according to the manufacturer’s instructions. In general, unfixed sperm cells are immersed in an agarose microgel on a slide incubated in an acid unwinding solution that transforms DNA breaks into single-stranded DNA, followed by immersion in a lysing solution to remove protamines. After staining, the spermatozoa without fragmented DNA show stained nucleoids with big halos of spreading of DNA loops, whereas those with fragmented DNA appear with a small or no halo. The halo sizes and fragmentation index were assessed using the “SCA DNA fragmentation” module.
Data are shown as mean ± standard deviation (SD) unless stated differently. All data were checked for normal distribution, and parametric tests were applied. For nonnormal cases, either the Kruskal–Wallis nonparametric test was used or data were corrected using logarithmic transformation prior to further assessments. Multivariate two-way analysis of variance (MANOVA) was used to compare differences in weight, lipid profile parameters (cholesterol triglyceride, HDL, and LDL), hormones (LH, FSH, and testosterone), and semen kinematic parameters in a full factorial model with pain group (pain and no pain) and weight group (lean and overweight) as the factors in this model. A
All participants completed the study and no safety issues were reported or recorded following the procedures applied in the study sessions.
Overweight and lean chronic pain patients reported their minimum pain intensity levels of 5.15 ± 2.21 and 4.7 ± 1.97 cm and maximum peak pain intensities of 7.78 ± 1.97 and 8.01 ± 1.77 cm on the VAS, respectively, which corresponded to their pain within the last 3 months.
Figure
Superimposed pain distribution areas as indicated in OP (overweight chronic pain, (a)) and LP (lean chronic pain, (b)) patients.
No statistically significant difference in pressure pain thresholds (PPTs) was observed in any of the assessed spots between the subgroups. However, pain groups (LP and OP) demonstrated a trend towards lower pain thresholds compared with the control groups (LC and OC) (Table
Pressure pain threshold values in overweight pain patient (OP), overweight control patient (OC), lean pain patient (LP), and lean control patient (LC) in 16 different test points in the body. Provided values are mean ± standard deviation. Multivariate two-way analysis of variance (MANOVA) was used to compare differences in each parameter in pressure pain thresholds.
Group test point | LC | LP | OC | OP | ||||
---|---|---|---|---|---|---|---|---|
Mean | Std. deviation | Mean | Std. deviation | Mean | Std. deviation | Mean | Std. deviation | |
p1: Vastus medialis muscle | 386.29 | 134.97 | 231.84 | 103.78 | 366.24 | 155.36 | 211.37 | 154.97 |
p2: Rectus femoris | 457.84 | 192.78 | 241.20 | 78.95 | 351.00 | 172.91 | 221.41 | 181.40 |
p3: Vastus lateralis muscle | 369.40 | 221.56 | 227.64 | 82.77 | 325.52 | 210.58 | 190.75 | 177.75 |
p4: Adductor longus muscle | 305.93 | 137.61 | 291.75 | 113.72 | 289.77 | 149.49 | 110.35 | 96.00 |
p5: Tibialis anterior muscle | 355.74 | 197.83 | 244.14 | 107.21 | 277.60 | 161.21 | 178.05 | 149.39 |
p6: Peroneus longus muscle | 404.23 | 198.05 | 247.66 | 102.08 | 304.76 | 174.70 | 227.83 | 144.37 |
p7: Patellar tendon | 460.37 | 316.30 | 217.08 | 67.81 | 282.99 | 102.49 | 207.53 | 200.58 |
p8: pes anserinus bursae | 316.84 | 174.43 | 225.36 | 82.27 | 276.56 | 155.86 | 200.82 | 112.23 |
p9: Popliteous muscle | 332.07 | 197.19 | 272.26 | 90.40 | 295.79 | 161.76 | 244.15 | 168.62 |
p10: Iliacus muscle | 399.08 | 91.24 | 244.86 | 133.52 | 318.13 | 135.21 | 228.00 | 149.85 |
p11: Quadrates lumborum muscle | 283.61 | 124.37 | 233.43 | 66.02 | 254.01 | 186.66 | 227.16 | 102.97 |
p12: Supraspinous ligaments area between L5–S1 and S1–S2 | 304.00 | 154.53 | 289.28 | 109.48 | 296.07 | 170.83 | 217.15 | 119.43 |
p13: Extensor digitorum brevis | 252.22 | 73.37 | 207.25 | 96.08 | 230.14 | 104.66 | 183.10 | 90.70 |
p14: Extensor digitorum brevis | 317.94 | 128.46 | 239.44 | 126.77 | 242.30 | 74.64 | 224.30 | 146.16 |
p15: Extensor hallucis longus | 297.27 | 173.54 | 198.99 | 49.99 | 256.87 | 188.01 | 245.38 | 62.91 |
p16: Flexor halluces longus | 252.70 | 148.90 | 235.00 | 116.33 | 257.00 | 93.43 | 190.20 | 55.60 |
Control: Deltoids | 358.38 | 128.38 | 244.91 | 126.80 | 260.58 | 100.78 | 232.87 | 110.40 |
None of the ANOVA results are significant.
Semen analysis parameters were assessed using the SCA, and the results are summarized in Table
Sperm quality parameters in overweight with chronic pain (OP), overweight control (OC), lean with chronic pain (LP), and lean control (LC). Provided values are median (25–75 percentiles), and superscripted letters mark pairwise significant differences (
OP | OC | LP | LC | |
---|---|---|---|---|
Motility (WHO [ |
||||
Concentration (m/ml) | 37.4 (31.9–92.3) | 63.9 (45.3–78.5) | 16.2 (8.0–50.3) | 49.8 (23.9–100.9) |
Immotile (%) | 22.3 (13.0–44.5) | 28.9 (19.6–42.7) | 40.9 (39–48.7) | 29 (12.1–57.0) |
Nonprogressive motile (%) | 50.5 (31.3–62.6) | 26.35 (23.7–32.8) | 28 (23.9–34.075) | 22.85 (16.9–25.5) |
Progressively motile (%) | 24.2 (23.3–25.0) | 39.5 (26.1–57.7)b | 29.7 (22.8–33.4)a | 42.6 (22.7–66.7)a,b |
Hyperactivated sperm (%) | 5.15 (2.0–10.4) | 12.6 (5.9–17.6) | 4.1 (1.8–4.6) | 10.7 (4.7–24.1) |
DNA fragmentation (%) | 41.7 (30.3–65.3) | 41.3 (28.1–66.7) | 55.4 (39.2–72.0) | 29 (16.5–76.1) |
Normal morphology (%) | 3.7 (3.1–6.5) | 5 (2.7–13.8) | 8 (7.0–9.9) | 13.1 (7.4–20.6) |
Both lean and obese control groups demonstrated insignificantly higher mean concentrations compared with their respective chronic pain groups.
The LC group demonstrated a significantly higher percentage of progressively motile sperm (
Moreover, BMI demonstrated a significant influence on the percentage of sperm with progressively motility among both lean and overweight groups (
Chronic pain demonstrated a significant influence on VCL, STR, and WOB in overweight patients, with significantly decreased (
Median (25–75 percentiles) kinematic parameters of sperm motility in overweight with chronic pain (OP), overweight control (OC), lean with chronic pain (LP), and lean control (LC) groups. Superscripted letters mark pairwise significant differences (
Average kinematic parameters | OP | OC | LP | LC |
---|---|---|---|---|
VCL ( |
38.0 (27.2–39.4)a | 42.8 (40.85–63.1)a,b | 31.7 (28.4–36.3) | 47.5 (31.1–54.1)b |
VSL ( |
14.5 (11.2–21.5) | 18.7 (14.55–29.8) | 11.4 (10.3–14.1) | 17.6 (12.2–21.2) |
VAP ( |
20.9 (16.5–29.9) | 25.5 (20.45–39.9) | 17.0 (15.1–20.0) | 24.2 (17.0–28.3) |
LIN (%) | 36.8 (31.6–43.9) | 42.3 (35.6–46.0) | 36.8 (34.5–40.1) | 43.3 (36.8–46.8) |
STR (%) | 66.9 (63.1–72.8)a,b | 73.3 (70.95–76.1)a | 69.1 (63.5–70.8)b | 75.0 (68.6–76.2) |
WOB (%) | 51.2 (45.0–54.8)a,b | 57.3 (50.80–61.0)a | 55.2 (53.2–56.3)b | 56.8 (54.5–62.4) |
ALH ( |
2.8 (2.6–3.8) | 3.2 (2.90–3.3) | 2.5 (2.30–3.0) | 2.6 (2.3–2.9) |
BCF (HZ) | 5.1 (3.8–6.2) | 6.5 (5.9–6.7) | 4.8 (4.5–5.0) | 5.6 (4.9–6.1) |
VCL also showed a significantly (
There was no significant difference in the morphology and DNA fragmentation in lean and overweight chronic pain patients compared with the healthy controls. Both lean and obese chronic pain groups displayed a trend towards higher percentage of DNA fragmentation and lower percentage of normal morphology compared with the respective control groups (Table
The plasma testosterone levels remained within the reference ranges for the hormone (10.3–27.4 nmol/L) (“Testosterone (R-nr. 515)—Statens Serum Institut,” 2015) and did not show any significant difference between the lean and overweight chronic pain patients and their healthy controls. Both chronic pain (LP and OP) subgroups demonstrated a tendency towards lower average values of FSH and higher values of LH compared with the control group (Figure
Estimated marginal means of reproductive hormones in overweight pain patient (OP), overweight control patient (OC), lean pain patient (LP), and lean control patient (LC). Provided values are mean ± standard deviation. Multivariate two-way analysis of variance (MANOVA) was used to compare differences in lipid profile. None of the ANOVA results are significant.
There was a tendency towards higher cholesterol levels in the LP and OP groups compared with LC and OC groups (Table
Lipid profile values in overweight pain patient (OP), overweight control patient (OC), lean pain patient (LP), and lean control patient (LC). Provided values are median (25–75 percentiles). Multivariate two-way analysis of variance (MANOVA) was used to compare differences in lipid profile.
OP | OC | LP | LC | |
---|---|---|---|---|
Cholesterol (mmol/L) | 4.3 (3.7–5.0) | 4.3 (3.4–5.0) | 5.0 (4.6–5.5) | 4.4 (3.9–5.9) |
Triglyceride | 0.7 (0.5–1.0) | 1.0 (0.7–1.4) | 1.2 (0.9–1.6) | 0.7 (0.6–1.3) |
LDL (mg/dl) | 2.6 (2.0–3.2) | 2.6 (1.8–3.2) | 3.3 (2.6–3.6) | 2.5 (2.1–4.2) |
HDL (mg/dl) | 1.5 (1.3–1.8) | 1.3 (1.1–1.4) | 1.3 (1.1–1.4) | 1.2 (1.1–1.7) |
None of the ANOVA results are significant.
The novelty of this study resides in investigating the influence of musculoskeletal chronic pain as a factor by itself, or in combination with obesity, on sperm quality as a biomarker of fertility potential in men.
For the first time, we investigated sperm motility including detailed kinematic parameters, sperm morphology, DNA fragmentation, and reproductive hormone levels as biomarkers of male fertility in lean and overweight chronic pain patients compared with lean and overweight healthy controls.
Chronic pain and obesity have been advocated as independent risk factors for decreased serum testosterone levels and altered sperm fertility potential [
Chronic pain has also been considered as a drive for stress response, and this recurrent stressor effect on the HPA axis and GnRH axis has been demonstrated as a possible risk factor for testosterone decrease [
The demonstrated tendency for lower PPT values (higher sensitivity) in overweight chronic pain patients compared to overweight healthy matched controls supports the previous reports, suggesting that pain sensitivity may be mediated by sociocultural, psychological, and biological factors [
Androgens also play an essential regulatory role in spermatogenesis and the maturation and motility of the spermatozoa during their transportation through the epididymis and vas deferens [
The OP group also demonstrates lower median values of progressively motile sperm compared with the OC group; however, the difference remained insignificant. Previous studies have similarly reported that obesity has a negative correlation with testosterone levels and consequently sperm quality parameters, leading to decreased fertility potential [
It may be speculated that even the insignificant change of testosterone levels observed in this study may have an effect on the maturation process of the sperm, thereby affecting the sperm motility and kinematic parameters. On the other hand, despite the demonstrated lower tendency in testosterone levels for chronic pain patients compared with the related healthy control group, it still remained within the (lower) reference range, and therefore, a significant difference and more conclusive results could be expected in a larger sample size. Prospective data are necessary to confirm these findings and explain the possible mechanism involved in the effects of chronic pain on male sperm quality, especially the kinematic parameters.
Collectively, our results indicate that chronic pain has no or minimal effect on sperm morphology and DNA fragmentation but significantly reduces the percentage of progressively motile sperm in lean men and exerts a negative effect on sperm concentration and kinematic parameters, which can be considered as valuable biomarkers of male fertility potential. However, the adverse overlapping effect of obesity on sperm quality makes it difficult to propose the exact effect of musculoskeletal chronic pain on sperm quality in overweight patients.
The newer generation of CASA systems used to assess detailed motility and kinematics of sperm samples in this study has the capability of providing more precise and objective results than previous generations [
While sample size of this study may not preclude a type 2 error, the results strongly suggest that musculoskeletal chronic pain has a significantly negative influence on sperm quality, seen as a significantly lower percentage of progressively motile sperm in lean men.
Despite significantly lower values of VCL, STR, and WOB in the overweight men with chronic pain compared to healthy controls, no significant difference in the percentage of sperm in different motility groups was observed which could be related to the overlapping negative influence of obesity on the sperm parameters. Further investigation to discriminate the effect of overweight and chronic pain in cases where both complications exist is suggested to confirm this hypothesis. Further studies are also warranted to assess the possible preventive or treatment strategies to break the link between obesity, chronic pain, and sperm quality.
The authors declare that there are no conflicts of interest.
The authors would like to acknowledge the financial aid received from the Department of Health Science and Technology (Aalborg University, Denmark) for this study. Appreciation extends to Aalborg University Hospital for collaboration in recruiting patients and their technical support and to Dr. Afshin Samani for his excellent guidance in statistical analysis.