High-dose vitamin D to attenuate bone loss in patients with prostate cancer on androgen deprivation therapy: A phase 2 RCT

Abstract

Background:

Androgen deprivation therapy (ADT) inhibits prostate cancer growth. However, ADT causes loss of bone mineral density (BMD) and an increase in fracture risk; effective interventions for ADT-induced bone loss are limited.

Methods:

A phase 2 randomized controlled trial investigated the feasibility, safety, and preliminary efficacy of high-dose weekly vitamin D (HDVD, 50,000 IU/week) versus placebo for 24 weeks in patients with prostate cancer receiving ADT, with all subjects receiving 600 IU/day vitamin D and 1000 mg/day calcium. Participants were ≥60 years (mean years, 67.7), had a serum 25-hydroxyvitamin D level <32 ng/mL, and initiated ADT within the previous 6 months. At baseline and after intervention, dual-energy x-ray absorptiometry was used to assess BMD, and levels of bone cell, bone formation, and resorption were measured.

Results:

The HDVD group (N = 29) lost 1.5% BMD at the total hip vs. 4.1% for the low-dose group (N = 30; p = .03) and 1.7% BMD at the femoral neck vs. 4.4% in the low-dose group (p = .06). Stratified analyses showed that, for those with baseline 25-hydroxyvitamin D level <27 ng/mL, the HDVD group lost 2.3% BMD at the total hip vs 7.1% for the low-dose group (p < .01). Those in the HDVD arm showed significant changes in parathyroid hormone (p < .01), osteoprotegerin (p < 0.01), N-terminal telopeptide of type 1 collagen (p < 0.01) and C-terminal telopeptide of type 1 collagen (p < 0.01). No difference in adverse events or toxicity was noted between the groups.

Conclusions:

HDVD supplementation significantly reduced hip and femoral neck BMD loss, especially for patients with low baseline serum 25-hydroxyvitamin D levels, although demonstrating safety and feasibility in prostate cancer patients on ADT.

INTRODUCTION

Prostate cancer is often associated with significant bone loss (osteopenia or osteoporosis), even before treatment initiation.¹ Further exacerbating bone loss, patients with prostate cancer often receive androgen deprivation therapy (ADT) during the course of their treatment.^2–4 Older patients with prostate cancer are more likely than younger patients to be treated with ADT than with other modalities including watchful waiting, and the use of ADT is increasing.⁵ Approximately 50% of all patients with prostate cancer will receive ADT during their treatment, with a median treatment duration of 2 to 3 years.^{6, 7} Patients with prostate cancer on ADT incur a 5- to 10-fold greater annual loss of bone mineral density (BMD) than similarly aged men without cancer.^8–12 The highest rate of bone loss occurs during the first year of ADT; the rate of bone loss slows thereafter.¹³ In addition to significant BMD loss, loss of lean muscle mass on the order of 2% to 5% occurs shortly after ADT initiation.^14–16 As a result, men treated with ADT have up to a 7-fold increase in risk of fracture compared with age-matched cancer-free men,^17–20 resulting in a significantly increased mortality rate.²¹

Treatment options for ADT-induced bone loss are limited. Current guidelines recommend 800 IU/day of vitamin D and 1200 to 1500 mg/day of calcium for all ADT patients. Antiresorptive bone drugs like bisphosphonates and denosumab should be considered for those with baseline osteopenia or osteoporosis.²² However, bisphosphonates, although effective in increasing BMD in ADT patients, come with significant side effects, including atypical femoral fractures, upper gastrointestinal symptoms, and osteonecrosis of the jaw.^23–27 Atypical fractures are often attributed to the poor quality of newly formed bone, including suboptimal size, shape, microstructure, and mechanical properties.²⁵ Consequently, compliance with these drugs at 1 year is low (20%–75%),²⁸ and the US Food and Drug Administration (FDA) suggests limiting their duration of use.²⁹ Hence, there is a need for alternative therapies to maintain bone density during ADT, ideally with agents that can be initiated before bone loss occurs or before starting bone drugs.

High-dose vitamin D (HDVD) is a promising therapy to maintain bone density during ADT, complementing current guideline-supported treatments. Low 25-hydroxyvitamin D [25(OH)D] levels are common in patients with prostate cancer,³⁰ and studies show that 50,000 IU/week of vitamin D significantly boosts serum 25(OH)D levels in patients with cancer.^31–33 Recent research confirms the long-term safety of HDVD based on a 4-year randomized controlled trial (RCT), which was both safe and well-tolerated without increasing adverse events (AEs).³⁴ Caution should still be used with HDVD, especially when selecting participants based on 25(OH)D levels because research has shown HDVD can increase fracture risk in vitamin D–replete patients with preexisting osteoporosis.³⁵ Although vitamin D is crucial for bone health, there is no consensus on the ideal serum concentration. The Institute of Medicine recommends 600 IU of vitamin D daily for those aged <70 years and 800 IU for those aged ≥70 years, aiming to maintain serum 25(OH)D levels above deficiency (≥20 ng/mL) for optimal bone health. However, a 2019 ASCO Expert Panel reviewed vitamin D supplementation in ADT patients and found that the commonly recommended doses (600–1000 IU/day) are insufficientto prevent BMD loss, especially in the oncology setting, “in men undergoing ADT found that the (vitamin D) doses commonly recommended are inadequate to prevent the loss of BMD… standard dosing may not be adequate in the oncology setting.”³⁶

We conducted a phase 2 RCT investigating the feasibility, safety, and preliminary efficacy of HDVD (50,000 IU/week)for the prevention of BMD loss versus the Institutes of Medicine’s recommendation (800 IU/week) for 24 weeks in patients with prostate cancer receiving ADT. We also investigated markers of bone formation (bone-specific alkaline phosphatase [BSAP], procollagen type I N-propeptide [PINP], osteocalcin), bone resorption (N-terminal telopeptide of type 1 collagen [NTX] and C-terminal telopeptide of type 1 collagen [CTX]), and bone cell regulators (parathyroid hormone [PTH], osteoprotegerin [OPG], sclerostin) to further elucidate the mechanisms by which HDVD affects bone integrity.

METHODS

Study sites and participants

Following approval by the University of Rochester Research Subjects Review Board, the study coordinator in collaboration with the treating physician screened and approached patients after their outpatient visits at the University of Rochester Medical Center. A targeted enrollment of 75 subjects was planned over 26 months. Potential subjects were preliminarily deemed eligible if they had a confirmed diagnosis of stage I to IV prostate cancer with no bone metastases (patients with bone metastases were excluded because antiresorptive bone agents are needed and would significantly alter bone biomarkers and BMD changes), had started ADT within the past 6 months with an additional 6 months planned, were able to read English, and were aged 60 years or older. Subjects were excluded if they had taken antiresorptive bone agents (e.g. denosumab, bisphosphonates) during the previous year (or planned on taking them), had a myocardial infarction in the past year, did not have physician permission for fitness testing, had a history of hypercalcemia, and/or were diagnosed with stage IV chronic kidney disease. If subjects were interested and preliminarily eligible, informed consent was reviewed and signed and a blood draw was done to confirm final eligibility; a total serum calcium of ≤10.5 mg /dL, a serum 25-hydroxyvitamin D level of <32 ng/mL (75 nmol), and an estimated glomerular filtration rate of ≥30 within the past 30 days. The 25 (OH)D level of <32 ng/mL was chosen because this is often the level defined as vitamin D insufficiency and the cutoff associated with improvements in bone and other related outcomes such as muscle mass.^37–39

Trial design

At the baseline visit, subjects completed questionnaires, physical fitness testing, a dual-energy x-ray absorptiometry (DXA) scan, and a blood draw. Questionnaires included information on sociodemographics, fatigue, physical activity, and quality of life. A fasting blood draw was done to determine serum levels of vitamin D, calcium, and bone metabolism biomarkers. ADXA scan measured BMD for the lumbar spine (L1–L4) and the total hip, which includes the femoral neck, trochanter, intertrochanter, and Ward’s triangle. Subjects were then randomized in block sizes of four to one of two treatment arms. Subjects in arm 1 were assigned to receive weekly HDVD (50,000 IU/week; vitamin D₃, Bio-Tech Pharmacal) along with a daily multivitamin (800 IU/day vitamin D þ 210 mg/day calcium; Centrum Men’s Plus Minerals, Haleon) and calcium supplements (800 mg/day calcium; Turns Ultra, GlaxoSmithKline) for 24 weeks. A certificate of analysis showed our HDVD supplement contained 62,155 IU, 24% more than 50,000 IU, which is a typical practice to satisfy the FDA’s requirement for shelf life. Subjects in arm 2 were assigned to receive a weekly vitamin D placebo along with a daily multivitamin (800 IU/day vitamin D þ 210 mg/day calcium) and calcium supplements (800 mg/day calcium) for 24 weeks. All study investigators, study co-ordinators, and subjects were blinded; only the research pharmacist had access to group assignment. Blood draws at weeks 6 and 18 were scheduled as a safety check to assess serum calcium and serum 25 (OH)D levels. At weeks 12 and 24, participants returned to repeat the same procedures performed in the baseline assessment, with the exception of the DXA, which was repeated only at week 24. Compliance with the supplementation regimen was monitored through a pill count at 12 and 24 weeks.

Outcomes

Bone mineral densities of the lumbar spine (L1–L4), femoral neck, and total hip were measured by means of DXA at baseline and week 24. All BMD results were assessed in a blinded fashion by a reader at a central location (Clinical Research Center, University of Rochester Medical Center). Serum 25-hydroxyvitamin D tests were performed by Mayo Medical Labs using the following methods: deuterated stable isotope is added as internal standard. 25-Hydroxyvitamin D2, 25-hydroxyvitamin D3, and the internal standard are extracted. The extracts are then derivatized before being analyzed by liquid chromatography-tandem mass spectrometry using multiple reaction monitoring. 25-Hydroxyvitamin D2 and 25-hydroxyvitamin D3 are quantified and reported individually and as a sum. Bone biomarkers (bone resorption, bone formation, bone cell regulators) were measured at baseline and week 24. Serum samples were run in singlets (Luminex Magpix); a median of 50 beaded reactions per well was used to determine concentration per participant in pg/mL, which was quantified using MILLIPLEX Analyst software. MILLIPLEX xMAP human bone panel kits (EMD Millipore kit#HBNMAG-51 K) for targets osteocalcin, osteopontin, OPG, sclerostin, and PTH were used. All kits for each biomarker were from the same lot and run in tandem.

Enzyme-linked immunosorbent assay kits were used per manufacturer’s protocol for NTX, CTX, and BSAP, with all samples run in one batch and all kits for each analyte coming from the same lot. All samples were run by the same technician for consistency.

Safety

Calls were made to subjects every 2 weeks to assess study drug adherence, remind subjects about upcoming appointments, and evaluate any AEs. Our original intent was to set an upper limit for 25(OH)D of 150 ng/mL, in line with the clinical practice guidelines.³⁹ Despite these guidelines, the University of Rochester Research Subjects Review Board required we institute an upper limit of 70 ng/mL for 25 (OH)D levels. Participants with 25(OH)D > 70 ng/mL during the study were dose reduced to 50,000 IU every 2 weeks (25,000 IU/week). Serum 25(OH)D levels were rechecked within 3 weeks to ensure their levels dropped <70 ng/mL. If 25(OH)D levels were still >70 ng/mL following the first dosage reduction, participants were instructed in an additional dosage reduction to 50,000 IU every 4 weeks (12,500 IU/week) and had their levels rechecked within 3 weeks. If 25(OH)D values still exceeded 70 ng/mL, the participant was removed from the study. Once levels resumed <70 ng/mL, participants were maintained at that dosage. One participant in arm 1 had to be withdrawn from the study because of continued high levels even after a second dose reduction; this subject had no hypercalcemia.

Statistical considerations

The primary aim of the study was to obtain preliminary efficacy estimates (mean changes, SDs) of HDVD vs placebo for improving BMD in patients with prostate cancer on ADT at week 24, as measured by DXA. We originally planned a total accrual of 76 subjects, with a 20% assumed dropout rate, resulting in 60 evaluable subjects. Based on the results of recent vitamin D RCTs,⁴⁰ we performed post hoc secondary analyses that examined changes in BMD by group stratified by baseline serum 25(OH)D level. We originally planned to stratify by the Institute of Medicine definition of deficiency (<20 ng/mL vs ≥ 20 ng/mL), but we did not have enough subjects with baseline 25(OH)D levels <20 ng/mL, so we stratified by median to maximize statistical power. Last, we analyzed the change in serum biomarkers both within-group and between-group from baseline to week 24. Because the distributions of bone biomarkers were skewed, these values were −2 log-transformed to provide increased normality and were used in all statistical analyses.

Clinical and sociodemographic variables were evaluated with two-sided (α = 0.05) t tests for continuous variables and chi-square tests for categorical variables to assess differences between treatment arms. Analysis of covariance (ANCOVA) models, with arm as the main factor, corresponding baseline levels and baseline serum 25(OH)D as the covariate, and arm by baseline interaction, were used to evaluate treatment effects on the BMD outcomes. If the interaction term was found to be statistically nonsignificant (p ≥ .10), it was removed from ANCOVA models. Estimated within-group effects from ANCOVA models were expressed as mean difference from baseline to week 24. Additionally, effect sizes (ES) were calculated by dividing the mean change by the baseline SD of the study population. To determine whether changes were clinically significant, we defined the minimal clinically important difference as outcomes having an effect size of at least 0.3.⁴¹ The intent-to-treat principle was followed because multiple imputation was used on any subjects who had missing data. A sensitivity analysis showed multiple imputation estimates that accounted for missing data were very similar to the complete case analysis.

RESULTS

Study population

A total of 95 patients with prostate cancer undergoing ADT provided consent, with 70 patients meeting full eligibility criteria after screening for 25(OH)D levels. A total of 59 patients agreed to participate, with 52 (88%) patients completing the 24-week intervention (Figure 1). There were no differences in subject characteristics between subjects who did and did not complete the trial. Table 1 shows the baseline characteristics of the study group by arm. Baseline characteristics were generally well balanced between the two groups, although the difference in race by study arm approached statistical significance (p = .07). Overall, the majority of subjects were married/partnered, well educated, White, and an average of 20 months post diagnosis.

FIGURE 1.

CONSORT diagram.

TABLE 1.

Baseline characteristics of study population.

Mean age, years (SD)	Placebo (n = 30)		Vitamin D (n = 29)		p value
	67.8	4.35	67.5	6.36	.84
Race
White	27	93.1%	22	75.9%
Non-White	2	6.9%	7	24.1%	.07
Marital status
Married/long-term partner	24	82.8%	25	86.2%
Divorced/single	5	17.2%	4	13.8%	.71
Work status
Currently working	13	44.8%	11	37.9%
Retired/disability	16	55.2%	18	62.1%	.79
Education
College or graduate school	24	82.8%	23	79.3%
High school or less	5	17.2%	6	20.7%	.73
BMI, mean	29.4	4.60	29.9	4.80	.71
BMI, categorical
Normal	5	16.7%	4	13.8%
Overweight	12	40.0%	8	27.6%
Obese	13	43.3%	17	58.6%	.53
Exercise
Currently exercising	12	41.4%	13	44.8%
Not currently but plans to do so	11	37.9%	12	41.4%
Not currently and no plans	6	20.7%	4	13.8%	.88
Tumor stage
T1	4	14.3%	6	21.4%
T2	11	39.3%	13	46.4%
T3	13	46.4%	9	32.1%	.57
Lymph nodes
N0	19	67.9%	18	62.1%
N1 or higher	9	32.1%	11	37.9%	.78
Metastatic involvement
M0	26	92.9%	26	89.7%
M1a	2	7.1%	3	10.3%	.67
Days on ADT at baseline (SD)	57.0	18.0	59.0	17.4	.67
Mean 25(OH)D, ng/mL (SD)	26.5	5.84	24.1	5.42	.11
Mean serum calcium, mg/dL (SD)	9.1	0.45	9.1	0.37	.93

Abbreviations: 25(OH)D, 25-hydroxyvitamin D; ADT, androgen deprivation therapy; BMI, body mass index.

^aAll metastatic involvement was within lymph nodes.

Baseline mean 25(OH)D and calcium levels are also shown in Table 1, in which the placebo arm had a slightly higher 25(OH)D level (placebo = 26.5 ng/mL vs high-dose = 24.1 ng/mL; p = .11). Figure 2 shows the change in 25(OH)D levels over the course of 24 weeks. Serum 25(OH)D levels rose rapidly in the high-dose group, with an increase of 21.7 ng/mL by week 6 compared with an increase of 3.2 ng/mL (p < .01) in the placebo group at week 6. At week 24, 25(OH)D levels increased by 32.8 ng/mL for the high-dose group and 3.6 ng/mL for the placebo group (p < .01). Although there was a marked difference in 25(OH)D levels, there was no statistical difference in serum calcium levels between the arms at any time point (Figure 3). For the high-dose group, serum calcium levels rose until week 12, at which point calcium levels stabilized and decreased slightly by week 24. There was no difference in the change in serum calcium levels from baseline to week 24 between the high-dose (þ0.12 mg/dL) and placebo (þ0.23 mg/dL; p = .39) groups.

FIGURE 2.

Change in serum 25(OH)D levels. 25(OH)D indicates 25-hydroxyvitamin D.

FIGURE 3.

Change in serum calcium.

Bone mineral density

Table 2 shows the baseline, final, and change in BMD by bone site; change scores were adjusted for corresponding baseline BMD value and baseline 25(OH)D levels. HDVD was associated with increased BMD at the total hip and femoral neck compared with the placebo. In the HDVD group, BMD at the total hip and femoral neck increased by 2.6% (high-dose: −1.5% vs placebo: −4.1%; Cohen’s = 0.23; p = .03) and 2.8% (high-dose: −1.7% vs placebo: −4.4%; Cohen’s = 0.22; p = .06), respectively, over the placebo group at week 24. There was a 2% increase in BMD for the high-dose group compared with the placebo for the trochanter (high-dose: −1.0% vs placebo: −3.0%; Cohen’s = 0.14; p = .10), but the difference was not significant. The HDVD group lost slightly more bone in the total spine compared with the placebo group (high-dose: −1.2% vs placebo: −0.5%) but the difference was not significant (p = .56).

TABLE 2.

Change in BMD and T-score by bone site.

Bone site	Baseline			Follow-up		Change scorea
	Mean	SD	p value	Mean	SD	Mean	SE	%	Cohen’s d	p value
Total hip
BMD
Vitamin D	1.079	0.12		1.058	0.12	−0.016	0.03	−1.52
Placebo	1.055	0.12		1.016	0.11	−0.044	0.06	−4.13
Vitamin D - placebo	0.024		.48	0.042	0.11	0.027		2.61	0.23	.03
T-score
Vitamin D	0.11	0.82		0.04	0.76	−0.09	0.19
Placebo	0.05	0.92		−0.16	0.73	−0.29	0.35
Vitamin D - placebo	0.06		.78	0.20		0.20			0.23	.01
Femoral neck
BMD
Vitamin D	0.948	0.11		0.910	0.12	−0.016	0.04	−1.67
Placebo	0.904	0.11		0.886	0.10	−0.040	0.05	−4.44
Vitamin D - placebo	0.045		.16			0.024		2.77	0.22	.06
T-score
Vitamin D	−0.53	0.78		−0.790	0.86	−0.118	0.30
Placebo	−0.81	0.75		−0.958	0.69	−0.286	0.36
Vitamin D - placebo	0.28		.20			0.167			0.22	.08
Trochanter
BMD
Vitamin D	0.835	0.11		0.808	0.13	−0.008	0.03	−0.95
Placebo	0.797	0.11		0.792	0.11	−0.023	0.04	−2.95
Vitamin D - placebo	0.039		.23			0.016		2.00	0.14	.10
T-score
Vitamin D	−0.02	0.86		−0.223	0.95	−0.049	0.21
Placebo	−0.32	0.80		−0.357	0.80	−0.183	0.26
Vitamin D - placebo			.21			0.135			0.16	.06
Ward’s triangle
BMD
Vitamin D	0.674	0.13		0.641	0.14	−0.015	0.05	−2.27
Placebo	0.638	0.12		0.637	0.12	−0.019	0.10	−3.02
Vitamin D - placebo	0.036		.31			0.004		0.75	0.03	.86
T-score
Vitamin D	−1.25	1.01		−1.498	1.08	−0.112	0.35
Placebo	−1.52	0.86		−1.562	0.81	−0.176	0.68
Vitamin D - placebo	0.16		.30			0.065			0.07	.67
Total spine
BMD
Vitamin D	1.253	0.21		1.241	0.19	−0.015	0.30	−1.20
Placebo	1.236	0.21		1.250	0.22	−0.006	0.29	−0.49
Vitamin D - placebo	0.017		.76			−0.009		−0.71	−0.04	.56
T-score
Vitamin D	0.73	1.79		0.62	1.67	−0.129	0.42
Placebo	0.57	1.83		0.72	1.89	−0.029	0.49
Vitamin D - placebo	0.16		.74			−0.100			−0.06	.46

Abbreviation: BMD, bone mass density.

^aAdjusted for corresponding baseline BMD and baseline serum 25-OH vitamin D.

Table 3 displays the results of the change in BMD stratified by baseline 25(OH)D level (median: <27 ng/mL vs ≥ 27 ng/mL). HDVD therapy was associated with significantly increased BMD of the total hip and femoral neck in subjects with lower baseline 25(OH)D levels. Among subjects with baseline 25(OH)D levels <27 ng/mL, the HDVD group had an absolute difference of 4.8% in BMD of the total hip (high-dose: −2.3% vs placebo: −7.1%; Cohen’s = 0.42; p < .01). A larger absolute difference of 5.9% was noted at the femoral neck for the high-dose group with lower baseline 25(OH)D levels (high-dose: −2.2% vs placebo: −8.0%; Cohen’s = 0.43; p = .03). There were no between-group differences in BMD at the trochanter (p = .36), Ward’s triangle (p = 0.17), and the total spine (p = .20).

TABLE 3.

BMD and T-score change stratified by baseline 25(OH)D.

Bone Site	Baseline 25(OH)D < 27 ng/mL					Baseline 25(OH)D ≥ 27 ng/mL
	Change scorea					Change scorea
	Mean	SE	%	Cohen’s d	p value	Mean	SE	%	Cohen’s d	p value
Total hip
Vitamin D	−0.025	0.008	−2.3			−0.013	0.015	−1.2
Placebo	−0.077	0.014	−7.1			−0.028	0.011	−2.7
Vitamin D - placebo	0.052	0.016	4.8%	0.42	<.01	0.015	0.019	1.5	0.13	.44
Total hip - T-score
Vitamin D	−0.151	0.058				−0.065	0.100
Placebo	−0.481	0.095				−0.201	0.068
Vitamin D - placebo	0.330	0.111		0.41	<.01	0.136	0.121		0.19	.27
Femoral neck
Vitamin D	−0.021	0.012	−2.2			−0.019	0.013	−2.0
Placebo	−0.075	0.020	−8.0			−0.024	0.009	−2.6
Vitamin D - placebo	0.054	0.024	5.9	0.43	.03	0.005	0.015	0.6	0.05	.76
Femoral neck - T-score
Vitamin D	−0.156	0.094				−0.144	0.085
Placebo	−0.601	0.153				−0.142	0.058
Vitamin D - placebo	0.445	0.179		0.54	.02	−0.002	0.104		0.00	.99
Trochanter
Vitamin D	−0.015	0.008	−1.9%			−0.002	0.011	−0.2
Placebo	−0.030	0.014	−3.8%			−0.018	0.007	−2.3
Vitamin D - placebo	0.015	0.016	1.9	0.15	.36	0.016	0.013	2.0	0.13	.25
Trochanter - T-score
Vitamin D	−0.106	0.063				−0.007	0.079
Placebo	−0.250	0.102				−0.133	0.053
Vitamin D – placebo	0.144	0.120		0.20	.24	0.126	0.098		0.13	.21
Ward’s triangle
Vitamin D	−0.029	0.019	−4.3			0.005	0.024	0.8
Placebo	0.023	0.031	3.5			−0.030	0.016	−4.8
Vitamin D - placebo	−0.052	0.037	−7.8	−0.36	.17	0.035	0.029	5.6	0.33	.23
Ward’s triangle - T-score
Vitamin D	−0.224	0.116				0.050	0.183
Placebo	0.030	0.191				−0.223	0.126
Vitamin D - placebo	−0.253	0.224		−0.23	.27	0.273	0.222		0.34	.23
Total spine
Vitamin D	−0.019	0.014	−1.5			0.004	0.015	0.3
Placebo	0.015	0.022	1.1%			−0.018	0.010	−1.5
Vitamin D - placebo	−0.034	0.026	−2.6	−0.18	0.20	0.023	0.019	1.9	0.11	.23
Total spine - T-score
Vitamin D	−0.163	0.128				0.030	0.138
Placebo	0.158	0.193				−0.138	0.091
Vitamin D - placebo	−0.321	0.232		−0.20	.18	0.168	0.167		0.10	.32

Abbreviation: 25(OH)D, 25-hydroxyvitamin D.

^aAdjusted for corresponding baseline BMD and baseline serum 25-OH Vitamin D.

Bone biomarkers

The change in bone biomarkers by group assignment is shown in Table 4. Both groups experienced a significant decrease in PTH from baseline to follow-up, but there was no between-group difference (high-dose: −0.44 pg/mL vs placebo: 0.32 pg/mL; p = .55). Levels of osteoprotegerin and sclerostin increased for the high-dose group but did not reach between-group statistical significance (p = .10 and p = .09, respectively) compared with the placebo group. The bone formation markers BSAP and osteocalcin increased for both groups, with no difference between the groups (p = .67 and p = .16, respectively). Bone resorption markers CTX and NTX increased across the study, with the high-dose group having significantly higher levels at follow up (p = 0.02 and p = .01, respectively) versus the placebo group.

TABLE 4.

Change in bone biomarkers by group.

	Baseline			Follow-up			Change scorea
	N	Mean	SD	N	Mean	SD	Delta changea	SE	Within-group Cohen’s da	p value	Between-group Cohen’s da	p value
PTH (pg/mL)
Vitamin D	25	4.95	1.11	24	4.52	0.80	−0.52	0.18	−0.46	.02
Placebo	27	4.32	1.17	27	4.14	1.15	−0.39	0.16	−0.34	<.01
Vitamin D – placebo		0.64	1.14		0.38	1.01	−0.13	0.24			−0.11	.60
Osteoprotegerin (pg/mL)
Vitamin D	25	8.34	0.54	24	8.46	0.52	0.18	0.08	0.26	.04
Placebo	27	8.09	0.80	27	8.19	0.44	0.02	0.08	0.03	.80
Vitamin D - placebo		0.25	0.69		0.27	0.48	0.16	0.11			0.23	.16
Sclerostin (pmol/L)
Vitamin D	25	11.00	0.94	24	11.21	1.03	0.15	0.07	0.15	.05
Placebo	27	10.98	1.04	27	11.13	1.01	0.04	0.07	0.04	.52
Vitamin D - placebo		0.02	0.99		0.08	1.02	0.11	0.10			0.11	.09
Osteocalcin (pg/mL)
Vitamin D	24	10.45	1.91	23	11.18	1.78	0.64	0.19	0.35	<.01
Placebo	27	11.17	1.75	27	11.64	1.57	0.45	0.18	0.25	.01
Vitamin D - placebo		−0.72	1.83		−0.46	1.67	0.19	0.26			0.10	.47
BSAP (μg/L)
Vitamin D	25	3.86	0.45	23	4.01	0.48	0.16	0.18	0.32	.36
Placebo	27	3.73	0.54	25	3.70	0.98	−0.11	0.16	−0.22	.49
Vitamin D - placebo		0.13	0.50		0.32	0.78	0.27	0.24			0.54	.26
PINP (μg/L)
Vitamin D	22	15.84	0.80	20	16.24	0.78	0.41	0.11	0.53	<.01
Placebo	27	15.72	0.77	27	16.02	0.69	0.32	0.10	0.41	.01
Vitamin D - placebo		0.12	0.78		0.23	0.73	0.09	0.15			0.12	.55
Osteopontin (ng/mL)
Vitamin D	25	12.36	2.31	24	12.13	2.09	0.06	0.31	0.03	.84
Placebo	27	12.29	1.58	27	11.96	2.38	−0.26	0.30	−0.13	.39
Vitamin D - placebo		0.08	1.97		0.16	2.25	0.32	0.43			0.16	.46
CTX (BCE/mmol creatinine)
Vitamin D	25	−1.44	0.57	25	−1.08	0.56	0.51	0.11	0.80	<.01
Placebo	27	−1.64	0.71	27	−1.26	0.67	0.37	0.10	0.58	<.01
Vitamin D - placebo		0.21	0.64		0.19	0.62	0.14	0.15			0.22	.36
NTX (BCE/mmol creatinine)
Vitamin D	25	1.48	0.54	25	1.79	0.60	0.31	0.06	0.70
Placebo	27	1.41	0.34	27	1.49	0.33	0.07	0.06	0.16	.19
Vitamin D - placebo		0.07	0.45		0.30	0.48	0.24	0.08			0.54	.01

Abbreviations: BCE, bone collagen equivalence; BSAP, bone-specific alkalaine phosphatase; CTX, C-terminal telopeptide of type 1 collagen; NTX, N-terminal telopeptide of type 1 collagen; PINP, procollagen type I N-propeptide.

^aAdjusted for corresponding baseline biomarkers level.

Safety

Overall, the rate of AEs in this RCT was low (Table 5). The most common AE was hypercalcemia, which was expected to be the most common AE based on previous RCTs of vitamin D supplementation. There were two grade 1 hypercalcemia AEs in the high-dose group and three grade 1 hypercalcemia AEs in the placebo group (p = .74). All hypercalcemia events were grade 1, asymptomatic, did not require any intervention, and resolved on their own. There were no significant differences in any of the other AEs between the groups. There was a death in the placebo group, resulting from infection and organ failure, which was unrelated to the study.

TABLE 5.

Adverse events by group.

	Arm 1: vitamin D (n = 29)							Arm 2: placebo (n = 30)
	CTCAE grade							CTCAE grade
Adverse event	None	1	2	3	4	5	Any	None	1	2	3	4	5	Any
Confusion	29	0	0	0	0	0	0	30	0	0	0	0	0	0
Constipation	29	0	0	0	0	0	0	30	0	0	0	0	0	0
Headache	28	1	0	0	0	0	1	29	1	0	0	0	0	1
Heart palpitations	29	0	0	0	0	0	0	30	0	0	0	0	0	0
Hypercalcemia	27	2	0	0	0	0	2	28	3	0	0	0	0	3
Hyperglycemia	28	0	1	0	0	0	1	29	0	1	0	0	0	1
Hyperphosphatemia	29	0	0	0	0	0	0	30	0	0	0	0	0	0
Multiorgan failure	29	0	0	0	0	0	0	29	0	0	0	0	1	1
Nausea	29	0	0	0	0	0	0	30	0	0	0	0	0	0
Poor appetite	29	0	0	0	0	0	0	30	0	0	0	0	0	0
Presyncope	29	0	0	0	0	0	0	29	1	0	0	0	0	1
Renal calculi	28	1	0	0	0	0	1	30	0	0	0	0	0	0
Vomiting	29	0	0	0	0	0	0	30	0	0	0	0	0	0
Weakness	29	0	0	0	0	0	0	30	0	0	0	0	0	0
Weight loss	29	0	0	0	0	0	0	30	0	0	0	0	0	0
Total		4	1	0	0	0	5	Total	5	1	0	0	1	7
High vitamin D (>70ng/mL)	21	8	0	0	0	0	8	30	0	0	0	0	0	0

Abbreviation: CTCAE, Common Terminology Criteria for Adverse Events Version 4.0.

DISCUSSION

In this 24-week RCT of patients with prostate cancer beginning ADT therapy, we found HDVD supplementation significantly reduced the amount of hip BMD loss (Cohen’s d = 0.23; p = .03) versus the control group. When stratified by the baseline median 25(OH)D level, those with levels <27 ng/mL in the high-dose group had an even larger, clinically significant reduction in BMD loss, specifically at the total hip (Cohen’s d = 0.42; p < .01) and femoral neck (Cohen’s d = 0.43; p = .03). Significant differences in BMD were limited to the total hip and femoral neck; not all bone sites benefited because between-group differences were not found at the trochanter, Ward’s triangle, or the total spine.

For the study cohort, BMD at baseline was generally in the normal range, with few subjects having osteopenia. The highest baseline BMD was at the spine, with a mean T-score of 0.7 compared with a mean T-score of 0.1 for the total hip and a mean T-score of −1.6 for the femoral neck. Overall, the rate of osteopenia at baseline was low (14% at the hip, 23% at the spine), and there were no subjects with osteoporosis. For this study, the greatest effects of HDVD were at bone sites that had the lowest baseline BMD (femoral neck and total hip).

HDVD supplementation worked rapidly to increase 25(OH)D levels because the HDVD group increased by more than 22 ng/mL byweek 6, compared with an increase of less than 3 ng/mL for the placebo group at week 6. In general, 25(OH)D levels plateaued around week 12 and remained relatively stable for the remainder of the study. A similar pattern was noted for serum calcium; levels peaked at week 1 2 and remained at the same level through the rest of the study. There were no between-group differences in mean calcium at anytime point. Additionally, there was no difference in the number of hypercalcemia events between the groups, with all hypercalcemia events being grade 1 and needing no intervention. These results demonstrate that 50,000 IU/week of vitamin D safely and rapidly increased serum 25(OH)D levels with minimal effects on serum calcium and a low rate of adverse events over 24 weeks.

Currently available bone drugs such as bisphosphonates and RANKL inhibitors have well-elucidated mechanisms,^42–44 whereas the mechanisms by which vitamin D influences bone health are not fully understood.^45,46 With this in mind, we tested markers of bone formation (BSAP, PINP, osteocalcin), bone resorption (NTX and CTX), and bone cell regulators (PTH, OPG, sclerostin). As expected, we saw PTH decrease in both groups. The high-dose group had increases in both bone formation makers OPG and sclerostin, but fell short of statistical significance (p = .10 and p = .09, respectively). The most important finding was a significant increase in bone resorption (NTX and CTX) for the HDVD group. This finding was expected because numerous other RCTs have shown significant increases in bone resorption following vitamin D supplementation.^47–49 Although levels of biomarkers of bone resorption increase in response to vitamin D, research shows the ability of osteoclasts to resorb bone is significantly decreased.^50,51 This reduction in resorption may be due to a reduced ability for cellular surface adhesion and reduction in migration.⁵² Furthermore, HDVD may increase resorption through an increase in osteoclast precursors.⁵³ OPG blocks osteoclast function by acting as a decoy receptor for RANKL.^54,55 Our study showed a significant increase in OPG activity for the high-dose group, which would significantly decrease the actual level of bone resorption despite higher biomarker levels. Overall, our biomarker data suggest that HDVD played a significant role in osteoclast differentiation based on increased CTX, NTX, and OPG, potentially explaining the paradoxical finding of increased BMD and increased resorption biomarker levels. Nevertheless, confirmatory research is needed before any conclusions can be drawn.

Although bisphosphonates and RANKL inhibitors are usually recommended after significant bone loss has already occurred (T-score < −1.5), our idea is that HDVD can be used before significant bone loss as a preventive agent. Although this study shows a significant effect of HDVD on hip BMD, the effect sizes we reported are lower than the effect sizes of currently available bone drugs.⁵⁶ Although bisphosphonates and RANKL inhibitors are extremely effective at increasing BMD and preventing fractures, they are hampered by a poor compliance rate and side effects.^{57, 58} In addition, the FDA and researchers have suggested limiting the total duration of use of bisphosphates because the benefit of these drugs may be limited beyond 5 years of use.^{59, 60} Based on these considerations and its demonstrated safety, HDVD might be an additional option to prevent bone loss in high-risk populations such as 25(OH) D-deficient ADT patients. It would be advantageous to employ a low-risk intervention like HDVD to prevent bone loss and delay the use of these bone drugs.

There are a number of limitations of this study, many of which can be addressed in future research. Our study lasted only 24 weeks, a short time to observe changes in BMD via DXA. It is possible that the duration of the intervention was too short to observe the effect on certain skeletal sites, such as the lumbar spine. Future studies should aim for an intervention of 1 year or longer, as is the standard in trials testing bone drugs, to fully understand the effects of HDVD. This study excluded subjects on bisphosphonates or RANKL inhibitors so that we could observe the effect of vitamin D alone on both BMD and bone biomarkers. However, growing evidence suggests that bisphosphonates combined with vitamin D are significantly more effective than bisphosphonates alone, and future trials of these bone drugs should look to incorporate vitamin D supplementation to increase efficacy.^{61, 62} Furthermore, generalizability is limited because of the small sample size, lack of African American participants, and limited geographic area from which subjects were recruited. African Americans generally have lower 25(OH)D levels,⁶³ and the effects of HDVD on this population need further study. Future studies should look to increase the sample size and recruit subjects from distinct geographical areas (multicenter studies) to increase the generalizability of future findings. Moreover, our results showed the benefits of HDVD were strongest in subjects with a baseline 25(OH)D < 27 ng/mL; other studies of HDVD have also shown a lack of effect in subjects with higher baseline vitamin levels.⁶⁴ Therefore, future studies should limit their study population to patients with 25(OH)D levels <27 ng/mL, as our results and the literature show there is limited benefit for those with higher baseline 25(OH)D levels. Last, although this study showed HDVD significantly increased serum 25(OH)D levels and reduced bone loss at the total hip, it remains unclear if this translates into decreased fracture risk or improves other clinically used measures. Further RCTs with longer study durations are needed to answer many of these questions.

In conclusion, HDVD supplementation was feasible, safe, and associated with a significant decrease in hip BMD loss in older men receiving ADT for prostate cancer, with the strongest effect observed in subjects with lower baseline serum 25(OH)D levels.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.