No association of serum PSA with vitamin D or total oxidant-antioxidant capacity in healthy men

Abstract

Background and aim: Vitamin D deficiency and oxidative stress were suggested to be related to prostate cancer risk. We aimed to investigate the association of serum PSA concentration with vitamin D and total oxidant/antioxidant levels.

Materials and methods: A total of 95 healthy men were enrolled for the cross sectional study. Serum PSA, 25(OH)D, serum total oxidant status, and total antioxidant status were measured.

Results: Serum PSA was significantly negatively correlated with serum total oxidant status (r= −0.309, p = .003) but there was no significant correlation between PSA and 25(OH)D (p = .383) or total antioxidant levels (p = .233). After adjustment for age BMI and smoking status with multiple regression analysis, there was no significant association between serum PSA and total oxidant status.

Conclusion: We find no evidence for an association between PSA and vitamin D levels or serum total oxidant/antioxidant levels.

Keywords:

• Vitamin D
• PSA
• BMI
• smoking
• total oxidant status

1. Introduction

Prostate cancer is the most common cancer in men and the widespread use of prostate specific antigen (PSA) screening increased the incidence rates of this disease [1]. Aging, family history, and race are non-preventable risk factors of prostate cancer [2]. By which mechanisms aging alters prostate carcinogenesis is not clear. Investigating aging related metabolic and hormonal factors may reveal the underlying mechanisms. Aging is related to reduced circulating 25(OH)D and 1,25(OH)₂ D as a result of decreased renal and skin production of vitamin D [3]. Vitamin D has effects on sexual hormones and metabolic parameters which can modify prostate cancer risk and deficiency of vitamin D was proposed as a risk factor for prostate carcinogenesis. There is evidence that vitamin D has apoptotic, anti-inflammatory, and anti-angiogenic effects on prostate cancer cells and administration of 1, (25) OHD₂ and vitamin D analogs inhibit growth of established tumors in animal models [4]. However, the results of epidemiological studies are inconclusive. Most of the studies reported that low vitamin D levels are not associated with increased risk of prostate tumor development [5–8]. Some studies demonstrated an association between low 25(OH)D concentrations and prostate tumor grade [9]. In addition to epidemiological studies a few intervention studies evaluated vitamin D and vitamin D analogs as therapeutic agents in prostate cancer. In patients with low risk prostate cancer vitamin D3 supplementation at 4000 IU decreased gleason scores in 55% of subjects [10] but in other studies administration of 1,25(OH)D did not show a clear beneficial effect [11,12].

Oxidative stress is another factor suggested to be involved in prostate cancer development and progression. Prostate cancer is strongly associated with aging and accumulation of oxidative damage is linked to aging process [13]. Intrinsic conditions such as metabolic alterations, androgen receptor activation and mutation-induced mitochondrial dysfunctions, extrinsic environmental factors such as inflammation, xenobiotic metabolism, and hypoxia may lead to increased reactive oxygen species (ROS) production in prostate cancer [14]. Although oxidative stress is regarded as a risk factor in prostate carcinogenesis antioxidant agents did not reduce prostate cancer incidence in some studies [15,16]. Serum PSA levels are known to be associated with prostate cancer risk. In the present study, we aimed to investigate the relation of serum 25(OH)D, serum total oxidant status, and serum total antioxidant status with PSA levels in healthy subjects.

2. Material and methods

2.1. Study population

Study population was recruited from males attending Tepecik Teaching and Research Hospital outpatient clinics during November 2013 and January 2014. Subjects eligible for the study were healthy males over 18 years of age. Exclusion criteria included prostatic cancer or other malignant diseases, inflammatory and metabolic diseases, use of any medications, and symptoms suggestive of prostatic disorders. Study was approved by local institutional review board and written informed consents were obtained from all participants.

2.2. Data collection and measurements

Data on demographic characteristics, medical history, and smoking status were obtained by interviewer-administered questionnaires. Weight and height of subjects were measured using standard protocols and BMI was calculated (kg/m²). Venous blood was collected from all participants into serum separator tubes with gel and centrifuged at 1300 g for 10 min. PSA was analyzed in fresh samples. Aliquoted serum was stored at −80 $°\mathrm{C}$ until total oxidant status and total antioxidant status analysis.

Serum PSA was measure using electrochemiluminescence immunoassay on Cobas E601 analyzer (Roche Diagnostics, Mannheim, Germany). Total oxidant status and total antioxidant status were measured on AU 5800 autoanalyzer with colorimetric method using commercially available kits (REL assay diagnostics, Mega Tip, Gaziantep, Turkey). Total oxidant status assay is a colorimetric assay based on the oxidation of the ferrous ion–chelator complex to ferric ion. The ferric ion makes a colored complex with chromogen in an acidic medium. The color intensity, which can be measured spectrophotometrically, is related to the total amount of oxidant molecules present in the sample. The assay is calibrated with hydrogen peroxide and the results are expressed in terms of micromole hydrogen peroxide equivalent per liter (μmol H₂O₂ Equiv./L). Total antioxidant status assay is based on the reduction of dark blue-green colored ABTS radical to colorless reduced ABTS form by antioxidants in the sample. The change of absorbance at 660 nm is related with total antioxidant level of the sample. The assay is calibrated with a stable antioxidant standard solution which is traditionally named as Trolox Equivalent that is a vitamin E analog.

2.3. Statistical analysis

The characteristics of the study participants were compared with Student’s t test and Chi-square test. Variables were checked for normal distribution with Kolmogorov–Smirnov test. Non-normally distributed variables were log transformed. Log (total oxidant status) and Log (PSA) was used for statistical analysis. Person correlation was used to assess the correlation between PSA and other variables. Multiple regression analysis was used to determine the independent relationship between PSA and other factors. SPSS software, version 17 (SPSS, Chicago, IL), was used for statistical analysis. p < .05 was considered as statistically significant.

3. Results

Of the 118 subjects invited for the study, 23 refused participation. A total 95 healthy males were included in the study. Biochemical and clinical characteristics of the study participants are presented in Table 1, overall and in different PSA groups. The mean age of the subjects was 43 ± 14 (range 18–77), and the mean BMI was 27.6 ± 4.6. There were 48 overweight and 26 obese men. 24 subjects was current or former smoker. Vitamin D concentrations of the subjects ranged from 6.3 to 43.5 ng/mL. About half (48%) of the study participants had vitamin D deficiency (<20 ng/mL). Age, BMI, total oxidant status, and smoking status were significantly different between PSA groups (p = .043, .006, .010, and .015, respectively) (Table 1).

Table 1. Biochemical and clinical characteristics of study participants.

		PSA
	Overall	<0.61 (ng/mL) (n = 47)	>0.61 (ng/mL) (n = 48)	p
Age	43 ± 14	40 ± 12	46 ± 16	.043^a
BMI (kg/m^2)	27.6 ± 4.6	28.9 ± 4.5	26.3 ± 4.5	.006^a
Total oxidant status (μmol H2O2 Equiv./L)	17.4 ± 13.1	20.5 ± 16.5	14.2 ± 7.0	.010^a
Total antioxidant status (Trolox Equiv.)	1.57 ± 0.17	1.59 ± 0.19	1.56 ± 0.17	.438^a
Vitamin D (ng/mL)	21.4 ± 7.8	21.3 ± 8.2	21.5 ± 7.6	.937^a
Smoking	24 (25.2%)	17 (36.2%)	7 (14.6%)	.015^b

^a Student t-test p values.

^b Chi-square p values.

Bold values indicate p < .05.

Circulating PSA concentrations was significantly correlated with age (r = 0.261, p = .011), BMI (r= −0.303, p = .003), total oxidant status (r= −0.309, p = .003), and smoking (r = 0.261, p = .011). Total antioxidant status and 25(OH) vitamin D levels were not significantly correlated with PSA (p = .233, p = .383, respectively). Multivariate linear regression analysis was performed with PSA as dependent variable. Variables significantly correlated with PSA were entered in the model as predictors of serum PSA concentrations. Regression analysis showed that age, BMI, and smoking was independently associated with PSA concentrations (p < .001, p = .001, and p = .006, respectively). Total oxidant status was marginally non-significant (p = .087) (Table 2).

Table 2. Multivariate regression model with log (PSA) as a dependent variable.

	B	Std. error	p
Constant	0.348	0.214	.109
Age	−0.198	0.071	<.001
BMI	0.009	0.002	.001
Smoking	−0.226	0.130	.006
Log (total oxidant status)	−0.023	0.007	.087
Model R^2 = 0.314

4. Discussion

It is well established that higher baseline PSA concentrations are associated with higher risk of developing prostate cancer [17,18]. Thus, a higher serum PSA value can be translated into higher risk of developing prostate cancer. This forms the rationale for the current study which investigated the association between suggested risk factors for prostate cancer and PSA concentrations.

Our results showed no association between serum 25(OH)D concentrations and PSA levels in healthy men. Although there is evidence that vitamin D has tumor suppressor effects on prostatic tissue [12,19] studies on the effect of vitamin D in preventing prostate cancer occurrence yielded inconclusive results [8]. In a study by Anic et al., vitamin D was not associated with PSA, similar to our results [20]. In another study by Chandler et al., the effect of vitamin D supplementation up to 4000 IU daily on PSA levels was investigated and no change in PSA was reported with vitamin D supplementation [21] in agreement with the results of our study. The inconsistency between different studies may be due to the different doses of vitamin D since studies reporting tumor suppressor effects on prostate cancer cells used large doses of vitamin D [12]. However, a vitamin D level at suboptimal range seems to be insufficient to show antitumor affects.

Testosterone and prostate volume are factors that can modify circulating PSA. Previous studies found a positive correlation between total testosterone and PSA [22–25]. Prostate volume is also known to be associated with PSA concentration. Although vitamin D was reported to be associated with higher circulating total testosterone and lower prostate volume, our study do not support a link between vitamin D and PSA concentration [22].

Our results also showed no association of PSA with total antioxidant status and total oxidant status. Furthermore, the direction of the association between PSA and total oxidant status was negative although being non-significant. There are substantial data supporting the role of oxidative stress in prostate cancer [13] but interventional studies did not report preventive effects for vitamin E supplementation [15,26]. The assays used for measurement of oxidative stress are different across studies. Our results do not support a role for serum oxidant status parameters in changing PSA levels. These results should be interpreted with caution because total oxidant and antioxidant status assays do not show directly prostatic tissue oxidative damage.

Age is a strong predictor of prostate cancer and known to be strongly correlated with PSA levels. In addition to age, our results showed that BMI and smoking are also negatively and significantly correlated with PSA levels in healthy man. These results are consistent with literature. It was reported that higher BMI values are associated with lower PSA levels [27,28].

One of the limitations of the study is that PSA is not an ideal marker for prostate cancer risk. Another limitation is cross-sectional design of the study. All measurements reflect a single point in time and do not shows temporal changes.

In conclusion, our findings show no association of PSA with serum 25(OH)D, total oxidant and antioxidant status in healthy men.

Disclosure statement

The authors declare that there is no conflict of interest.