Can we link Vitamin D deficiency to benign prostatic enlargement? An observational case control study

Benign prostatic enlargement (BPE) is one of the most prevalent ageing-related derangements in men and has a significant impact on quality of life (1). Prevalence of BPE ranges from 40-50% at the age of 50, 80% at the age of 70 and about 90% by the ninth decade (2). It is entrenched that normal, as well as malignant prostate cells, express vitamin D receptors (3), which are responsible for regulating cell growth and replication (4,5). Vitamin D3 and a few of its analogues can be used to modulate the growth and differentiation of prostatic cells (6). Consequently vitamin D deficiency could potentially be a modifiable risk factor for the prevention of BPE in addition to other risk factors like obesity, diabetes mellitus, diet and lifestyle (7). We aimed to study the association of prostatic volume, prostatomegaly grade and IPSS (International Prostate Symptom Score) with vitamin D deficiency if any.


Introduction
Benign prostatic enlargement (BPE) is one of the most prevalent ageing-related derangements in men and has a significant impact on quality of life (1). Prevalence of BPE ranges from 40-50% at the age of 50, 80% at the age of 70 and about 90% by the ninth decade (2). It is entrenched that normal, as well as malignant prostate cells, express vitamin D receptors (3), which are responsible for regulating cell growth and replication (4,5). Vitamin D3 and a few of its analogues can be used to modulate the growth and differentiation of prostatic cells (6). Consequently vitamin D deficiency could potentially be a modifiable risk factor for the prevention of BPE in addition to other risk factors like obesity, diabetes mellitus, diet and lifestyle (7). We aimed to study the association of prostatic volume, prostatomegaly grade and IPSS (International Prostate Symptom Score) with vitamin D deficiency if any.

Materials and methods
After obtaining approval from the Institutional Ethics Committee, an observational case-control study was conducted at Government Medical College, Calicut, Kerala, from May 2017 to December 2018. One fifty men aged between 50 to 75 years, presenting with BPE and LUTS with a negative urine dip for urinary tract infection and PSA<4 ng/ml were enrolled in the study. The sample size was decided based on the sample size of previous studies and the fulfilment of inclusion criteria. Successively all the patients were tested for serum 25-hydroxyvitamin D 25(OH) D level. Patients diagnosed with vitamin D deficiency were classified as "cases" and those with normal vitamin D levels were classified as "controls". All the patients had voluntarily consented to their inclusion in the study. Patients with a history of neurogenic bladder, stricture urethra, carcinoma of bladder or prostate, vesical calculi and serum PSA level > 4ng/ml were excluded from the study.
Key words: vitamin D deficiency, benign prostatic hyperplasia, prostate volume, IPSS Patients with PSA of more than 4ng/ml and a family history of prostatic malignancy were referred to a cancer clinic for further evaluation.

Clinical variables
The prostate gland was assessed by digital rectal examination for size grading and the Siemens ® Acuson X-300 colour Doppler machine was used for prostate volume measurement by a fixed assigned clinician. Participants were instructed to fill the International Prostate Symptom Score (IPSS) questionnaire in English/ Malayalam translation (8) which includes 7 questions, having each response scored from 0 to 5, giving a maximum score of 35. The response was graded as 0-7 being mildly symptomatic, 8-19 being moderately symptomatic, 20-35 being severely symptomatic. Prostatomegaly grading was done as per classification described by Romero et al (9). Working diagnosis of BPE was made depending on the presence of LUTS, prostate volume greater than 20 ml and serum PSA less than 4ng/ml.

Blood sampling and laboratory testing
For submitting blood samples patients were instructed to observe overnight fast and abstain from smoking for at least 12 hours. Centrifuged samples were immediately stored at-80°C before assay. The circulating form of vitamin D (25OHD) was assayed by liquid chromatography with mass spectrometry detection (LC-MS/MS). Eurolyser CUBE -S kit was utilized for measuring serum PSA levels. Vitamin D levels were classified as vitamin D deficiency (level <20ng/ml), vitamin D insufficiency (level -20-30ng/ml) and normal level (level >30ng/ml).

Statistical analyses
Results were expressed as medians (interquartile ranges) or (mean ± standard deviation) for the quantitative variables and percentages for qualitative variables.
Qualitative variables were compared between groups using the Chi-square test. Mann-Whitney U test was done to compare the difference in the distribution of DRE grades and IPSS. Quantitative variables were compared using the T-test. Participants were divided into 2 groups, based on serum 25(OH) D levels, namely, cases (BPE with vitamin D deficiency, level <20ng/ml) and control group (BPE with vitamin D insufficiency, level 20-30ng/ml or normal level >30ng/ml).
Associations of vitamin D deficiency with prostate volume, grade and IPSS were assessed using linear regression models in multivariate adjustment, for possible confounders. The results were expressed as odds ratios (ORs) with the corresponding 95% CI. Statistical significance was defined as P value <0.05. Statistical analysis was performed using SPSS for Windows (version 24.0. Armonk, NY: IBM Corp).

Results
Participants with vitamin D deficiency (cases) were older than those with normal vitamin D levels (controls). The age difference noted was statistically significant (P=0.035). The median age of cases was 61.04 whereas the median age of controls was 57.77. The BMI (Body Mass Index) was found to be significantly higher in cases compared to the controls (P=0.029). The mean BMI in cases was 22.66 Kg/m 2 and in controls, it was 21.54 Kg/m 2 .
The median serum level of 25(OH) D in the study participants was 18.95ng/ml. Vitamin D deficiency was detected in 70% of participants, which were classified as cases and the rest 30% were classified as controls. Compared to the controls the median serum level of 25(OH) D in the cases was significantly lower 12

Prostate volume
As shown in table 1, the mean prostate volume in the cases was 41.32ml, which was 23.42ml in controls. The difference between the two was statistically significant. The prostate volume was greater than 20ml in 65.1% of cases with vitamin D deficiency versus 34.2% of controls (P<.003). There was a significant negative correlation between 25(OH) D level and prostate volume, which suggests lower the 25(OH) D levels higher the prostate volume (r = -0.328, P<.001)

Prostatomegaly grade
When the grade of prostate size was assessed by digital rectal examination (DRE) in the cases its distribution was observed as 41.9%, 35.2% and 22.9% for grades I, II and III respectively. While in the controls its distribution was 62.67% and 33.33% for grades I and II respectively. None of the controls had grade III prostatomegaly. As table 1 depicts, this difference in the distribution of prostatomegaly grades was statistically significant (P=0.001).

Discussion
Although ageing and the presence of androgens are known to be the most important factors in the pathogenesis of BPE, the exact mechanism is still ambivalent. Ageing-related changes in the skin, renal function, gut absorption, and reduced sunlight exposure may adversely impact the formation of vitamin D in elderly men (10,11,12). The median age of the study population, as well as controls, was comparable with other studies (13,14). The median serum level of 25(OH) D in our participants was 18.95 ng/ml and vitamin D deficiency was detected in 70% of participants. We found that the mean prostate volume in vitamin D deficiency cases was 41.32 ml, which was significantly higher than 23.42 ml in controls. Our findings are complementary to the findings reported by Zhang et al (15). They observed that the median prostate volume in vitamin D deficiency was 42 ml and in the control group it was 28 ml. In line with our study, an inverse correlation between serum 25-OH D level <20 ng/ml and prostate volume was reported by Murphy et al (16).
Our study population was found to have significantly  (15). and Mohamed Elshazly et al (13). Unlike, Elshazly et al (15). we did not find any statistically significant association between serum PSA level and 25(OH) D level.
Our study was not devoid of limitations. Enlisting a few, we did not take into consideration age-specific PSA levels, instead, we used a PSA cut off <4 ng/ml. There is a possibility of seasonal variation of Vitamin-D levels in our patients, which was not taken into consideration. The median age and BMI of cases and controls were not comparable, acting as confounding factors.
To conclude, this study was aimed to demonstrate the relationship of vitamin D deficiency with prostate volume and severity of IPSS in men with BPE. The men having BPE and vitamin D deficiency were found to have a greater prostate volume, higher prostatomegaly grade on DRE and higher IPSS in comparison to men with BPE and normal vitamin D levels. If further studies confirm this association, vitamin D deficiency may be used as a therapeutic target for preventing and treating BPE.