Vitamin D supplementation and total cancer incidence and mortality by daily vs. infrequent large-bolus dosing strategies: a meta-analysis of randomised controlled trials

The effect of physical activity on vitamin D: A systematic review and meta-analysis of intervention studies in humans

Objectives

Cross-sectional studies demonstrate a positive association between higher physical activity and serum 25-hydroxyvitamin D (25(OH)D) concentration. However, whether this association is causal is unclear. We conducted a systematic review to identify intervention studies that examined the effect of physical activity on serum 25(OH)D concentration in humans.

Study design

Systematic review and meta-analysis.

Methods

We searched PubMed, Scopus and Web of Science to identify full-text peer-reviewed articles published in English from inception until January 2023. Eligible studies were randomised controlled trials or quasi-experimental studies. We used random effects meta-analysis to calculate the weighted mean difference (WMD) in the change in 25(OH)D concentration between physical activity and control groups. We used the revised Cochrane risk-of-bias tool for randomized trials (RoB 2) to assess the methodological quality of included studies.

Results

We included 32 articles in the systematic review and 24 in the meta-analysis. The intervention varied from resistance and weight-bearing exercises (n = 13) to aerobic exercises (n = 10), moderate and moderate-to-vigorous exercises (n = 5), aquatic exercise (n = 2), and multicomponent traditional exercises (n = 2) (Tai Chi and Yijinjing). The WMD in 25(OH)D in the physical activity and control groups was 9.51 and 4.87, respectively (between-group mean difference 4.64, p = 0.002). However, the difference was only evident in studies that implemented the intervention outdoors (n = 3; between-group mean difference 17.33, p < 0.0001); when the intervention was indoors there was no significant effect of physical activity on 25(OH)D (n = 16; between-group mean difference 1.80, p = 0.113).

Conclusions

This meta-analysis of physical activity interventions in humans showed that physical activity does not lead to increased 25(OH)D independently of time outdoors. However, most studies were under-powered, in many the exercise was low intensity, and vitamin D was not the primary outcome.

Vitamin D in tuberous sclerosis complex-associated tumors

Mammalian target of rapamycin inhibitors (mTORi) have been used to treat pediatric tuberous sclerosis complex (TSC)-associated tumors, particularly in cases with contraindications to surgery or difficulties in complete tumor resection. However, some patients experience side effects and tumor regression after discontinuation of the treatment. Therefore, there is an urgent need to develop drugs that can be used in combination with mTORi to increase their efficacy and minimize their side effects. 1,25-Dihydroxyvitamin D3 (1,25-D), which has anticancer properties, may be a promising candidate for adjuvant or alternative therapy because TSC and cancer cells share common mechanisms, including angiogenesis, cell growth, and proliferation. Vitamin D receptor-mediated signaling can be epigenetically modified and plays an important role in susceptibility to 1,25-D. Therefore, vitamin D signaling may be a promising drug target, and in vitro studies are required to evaluate the efficacy of 1,25-D in TSC-associated tumors, brain development, and core symptoms of psychiatric disorders.

Consensus Statement on Vitamin D Status Assessment and Supplementation: Whys, Whens, and Hows

The 6th International Conference, "Controversies in Vitamin D," was convened to discuss controversial topics, such as vitamin D metabolism, assessment, actions, and supplementation. Novel insights into vitamin D mechanisms of action suggest links with conditions that do not depend only on reduced solar exposure or diet intake and that can be detected with distinctive noncanonical vitamin D metabolites. Optimal 25-hydroxyvitamin D (25(OH)D) levels remain debated. Varying recommendations from different societies arise from evaluating different clinical or public health approaches. The lack of assay standardization also poses challenges in interpreting data from available studies, hindering rational data pooling and meta-analyses. Beyond the well-known skeletal features, interest in vitamin D's extraskeletal effects has led to clinical trials on cancer, cardiovascular risk, respiratory effects, autoimmune diseases, diabetes, and mortality. The initial negative results are likely due to enrollment of vitamin D-replete individuals. Subsequent post hoc analyses have suggested, nevertheless, potential benefits in reducing cancer incidence, autoimmune diseases, cardiovascular events, and diabetes. Oral administration of vitamin D is the preferred route. Parenteral administration is reserved for specific clinical situations. Cholecalciferol is favored due to safety and minimal monitoring requirements. Calcifediol may be used in certain conditions, while calcitriol should be limited to specific disorders in which the active metabolite is not readily produced in vivo. Further studies are needed to investigate vitamin D effects in relation to the different recommended 25(OH)D levels and the efficacy of the different supplementary formulations in achieving biochemical and clinical outcomes within the multifaced skeletal and extraskeletal potential effects of vitamin D.

The Power of Vitamin D: Is the Future in Precision Nutrition through Personalized Supplementation Plans?

In the last few decades, vitamin D has undeniably been one of the most studied nutrients. Despite our ability to produce vitamin D through sunlight exposure, its presence in several natural food sources and fortified foods, and its widespread availability as a dietary supplement, vitamin D deficiency is a serious public health problem, affecting nearly 50% of the global population. Low serum levels of vitamin D are being associated with increased susceptibility to numerous health conditions, including respiratory infections, mental health, autoimmune diseases, and different cancer types. Although the association between vitamin D status and health is well-established, the exact beneficial effects of vitamin D are still inconclusive and indefinite, especially when considering the prevention and treatment of different health conditions and the determination of an appropriate dosage to exert those beneficial effects in various population groups. Therefore, further research is needed. With constant improvements in our understanding of individual variations in vitamin D metabolism and requirements, in the future, precision nutrition and personalized supplementation plans could prove beneficial.

Personalization matters: the effect of sex in multivitamin-multimineral-based cancer prevention

The prevention of non-communicable diseases like cancer contributes to healthy aging. Dietary supplements might support such prevention; their effect likely depends on the personal characteristics of the individuals receiving them. To evaluate the influence of sex on reducing cancer incidence with multivitamin-multimineral (MVM) supplementation, sex-specific results of the efficacy of MVM supplementation for cancer prevention were collected and meta-analyzed (using fixed effect (FE) and random effect (RE) models). Three trials included in the "US Preventive Services Task Force Recommendation Statement Report regarding Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer" were used, namely, COSMOS, SU.VI.MAX, and PHS2. A total of 28,558 men and 20,542 women were included. Multivitamin-multimineral supplementation significantly reduced cancer incidence in the entire population (HR 0.93 [95% CI, 0.88-0.99], FE and RE); sex-specific meta-analysis showed beneficial effects of supplementation in men (HR 0.91 [95% CI, 0.85-0.97] (FE)/0.88 [95% CI, 0.77-1.01] (RE)); however, there was no effect in women (HR 1.00 [95% CI, 0.88-1.14], FR and RE); (Pdifference = 0.17). Sex could influence the effect of MVM supplementation in reducing cancer incidence, with supplementation being effective only in male individuals. These results might be informative for future research and public health policy makers.

Integrative Oncology Approaches to Reduce Recurrence of Disease and Improve Survival

PURPOSE OF REVIEW

After a cancer diagnosis, patients ask what they can do in addition to the recommended treatments to increase their survival. Many turn to integrative medicine modalities and lifestyle changes to improve their chances of survival. Numerous studies have demonstrated that lifestyle changes can significantly improve survival rates for cancer patients. Less support exists for the use of natural products or supplements to improve cancer survival. In this manuscript, we review key findings and evidence in the areas of healthy eating habits, physical activity, stress management and social support, and sleep quality, as well as natural products and supplements as they relate to the cancer recurrence and survival.

RECENT FINDINGS

While more research is needed to fully understand the mechanisms underlying the associations between lifestyle changes and cancer survival, findings suggest that lifestyle modifications in the areas of diet, physical activity, stress management and social support, and sleep quality improve clinical cancer outcomes. This is especially true for programs that modify more than one lifestyle habit. To date, outside of supplementing with vitamin D to maintain adequate levels, conflicting conclusion within the research remain regarding the efficacy of using natural products or supplement to improve cancer recurrence of disease or cancer survival. A call for further research is warranted. Lifestyle screening and counseling should be incorporated into cancer treatment plans to help improve patient outcomes. While the scientific community strives for the pursuit of high-quality research on natural products to enhance cancer survival, transparency, dialogue, and psychological safety between patients and clinicians must continue to be emphasized. Proactive inquiry by clinicians regarding patients' supplement use will allow for an informed discussion of the benefits and risks of natural products and supplements, as well as a re-emphasis of the evidence supporting diet and other lifestyle habits to increase survival.

Higher Vitamin D Levels before Methotrexate Therapy Initiation Are Associated with Lower Subsequent Mortality in Patients with Rheumatoid Arthritis

(1) Vitamin D deficiency is associated with mortality in the general population and has been observed in one rheumatoid arthritis (RA) cohort. Here, we investigate the relationship between 25-hydroxyvitamin D (25(OH)D) levels before methotrexate (MTX) therapy initiation in patients with RA and the subsequent all-cause mortality in a national Veterans Affairs (VA) cohort. (2) This is a retrospective study on RA patients time-oriented around the initial MTX prescription and 25(OH)D levels before starting MTX. We examined survival in patients with 25(OH)D levels > 50 nmol/L and ≤50 nmol/L using the Cox Proportional Hazard Model and fully adjusted for risk factors. (3) In total, 15,109 RA patients were included in the nationwide cohort. RA patients with 25(OH)D levels > 50 nmol/L before starting MTX had a 28% reduced risk of mortality when compared to those with levels ≤ 50 nmol/L (HR: 0.72, CI: 0.64-0.80, p < 0.001) after adjusting for traditional risk factors. (4) In this national RA cohort receiving standard-of-care MTX, patients with 25(OH)D levels > 50 nmol/L have a lower subsequent mortality when compared to those with 25(OH)D levels ≤ 50 nmol/L. It remains to be determined whether increasing Vitamin D levels in RA patients initially found to be Vitamin D deficient impacts their all-cause mortality.

Vitamin D status during and after treatment and ovarian cancer survival

PURPOSE

Five-year relative survival for ovarian cancer remains below 50%. Strategies to improve outcomes are needed. Higher serum 25-hydroxyvitamin D [25(OH)D] concentrations [measure of vitamin D status] at and before diagnosis have been associated with longer survival in cancer patients; however, data for ovarian cancer are limited. We aimed to determine if 25(OH)D concentrations during and after primary treatment were associated with ovarian cancer-specific survival.

METHODS

We used data from a nationwide prospective cohort study of women with ovarian cancer. Among 886 participants treated with chemotherapy, 700 (79%) had a blood sample collected during (n = 591) and/or after (n = 458) primary treatment. These were tested for 25(OH)D. Clinical and survival data were abstracted from medical records. We used multivariable Cox proportional hazards regression to estimate hazard ratios (HR) and 95% confidence intervals (CI) for associations between 25(OH)D and ovarian cancer-specific survival.

RESULTS

Mean 25(OH)D concentrations were lower during than after primary treatment (82 and 91 nmol/L, respectively); only 14% and 8% had concentrations below 50 nmol/L during and after primary treatment, respectively. There was no association between 25(OH)D and ovarian cancer-specific survival during five years of follow-up [HR 1.10 (95% CI: 0.76, 1.61) and 0.95 (0.54, 1.68) for the highest vs. lowest quintile during and after treatment, respectively].

CONCLUSIONS

We did not observe any association between serum 25(OH)D concentration and ovarian cancer-specific survival. Our results suggest that, in the absence of vitamin D deficiency, vitamin D supplementation to improve ovarian cancer survival is not warranted.

Health Effects of Vitamin D Supplementation: Lessons Learned From Randomized Controlled Trials and Mendelian Randomization Studies

Vitamin D plays an important role in calcium homeostasis and many cellular processes. Although vitamin D supplements are widely recommended for community-dwelling adults, definitive data on whether these supplements benefit clinically important skeletal and extraskeletal outcomes have been conflicting. Although observational studies on effects of vitamin D on musculoskeletal and extraskeletal outcomes may be confounded by reverse causation, randomized controlled studies (RCTs) and Mendelian randomization (MR) studies can help to elucidate causation. In this review, we summarize the recent findings from large RCTs and/or MR studies of vitamin D on bone health and risk of fractures, falls, cancer, and cardiovascular disease, disorders of the immune system, multiple sclerosis, and mortality in community-dwelling adults. The primary analyses indicate that vitamin D supplementation does not decrease bone loss, fractures, falls, cancer incidence, hypertension, or cardiovascular risk in generally healthy populations. Large RCTs and meta-analyses suggest an effect of supplemental vitamin D on cancer mortality. The existence of extraskeletal benefits of vitamin D supplementations are best documented for the immune system especially in people with poor vitamin D status, autoimmune diseases, and multiple sclerosis. Accumulating evidence indicates that vitamin D may reduce all-cause mortality. These findings, in mostly vitamin D-replete populations, do not apply to older adults in residential communities or adults with vitamin D deficiency or osteoporosis. The focus of vitamin D supplementation should shift from widespread use in generally healthy populations to targeted vitamin D supplementation in select individuals, good nutritional approaches, and elimination of vitamin D deficiency globally. © 2023 American Society for Bone and Mineral Research (ASBMR).

Serum 25-Hydroxyvitamin D Levels and Risk of Colorectal Cancer: An Age-Stratified Analysis

BACKGROUND & AIMS

The role of circulating 25-hydroxyvitamin D (25(OH)D) in the prevention of early-onset colorectal cancer (CRC) in young adults aged <50 years is uncertain. We evaluated the age-stratified associations (<50 vs ≥50 years) between circulating 25(OH)D levels and the risk of CRC in a large sample of Korean adults.

METHODS

Our cohort study included 236,382 participants (mean age, 38.0 [standard deviation, 9.0] years) who underwent a comprehensive health examination, including measurement of serum 25(OH)D levels. Serum 25(OH)D levels were categorized as <10, 10 to 20, and ≥20 ng/mL. CRC, along with the histologic subtype, site, and invasiveness, was ascertained through linkage with the national cancer registry. Cox proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for incident CRC according to the serum 25(OH)D status, with adjustment for potential confounders.

RESULTS

During the 1,393,741 person-years of follow-up (median, 6.5 years; interquartile range, 4.5-7.5 years), 341 participants developed CRC (incidence rate, 19.2 per 105 person-years). Among young individuals aged <50 years, serum 25(OH)D levels were inversely associated with the risk of incident CRC with HRs (95% CIs) of 0.61 (0.43-0.86) and 0.41 (0.27-0.63) for 25(OH)D 10 to 19 ng/mL and ≥20 ng/mL, respectively, with respect to the reference (<10 ng/mL) (P for trend <.001, time-dependent model). Significant associations were evident for adenocarcinoma, colon cancer, and invasive cancers. For those aged ≥50 years, associations were similar, although slightly attenuated compared with younger individuals.

CONCLUSIONS

Serum 25(OH)D levels may have beneficial associations with the risk of developing CRC for both early-onset and late-onset disease.

Vitamin D supplementation and cognition-Results from analyses of the D-Health trial

BACKGROUND

Observational studies have consistently found a link between low serum 25-hydroxyvitamin D concentration and higher risk of cognitive impairment. Results from randomized controlled trials have been mixed, and few have been conducted in the general population.

METHODS

We recruited 21,315 community-dwelling Australians aged between 60 and 84 years to participate in the D-Health Trial, a randomized, double-blind, placebo-controlled trial. The intervention was monthly oral doses of 60,000 international units of vitamin D or placebo for 5 years. We assessed cognitive function in a randomly sampled group of participants aged ≥70 years using the Telephone Interview for Cognitive Status (TICS) at 2 and 5 years after randomization. The primary outcome for this analysis was TICS score; the secondary outcome was the proportion of people who had cognitive impairment (defined as TICS score ≤25). We analyzed data using mixed models (linear and logistic).

RESULTS

We interviewed 3887 participants at year 2 and 3614 participants at year 5. The mean TICS score at these time points was 32.3 and 32.2, respectively. Vitamin D supplementation did not affect cognitive function as measured by TICS score (mean difference between vitamin D and placebo groups 0.04; 95% CI -0.14 to 0.23), or alter risk of cognitive impairment (odds ratio 1.00; 95% CI 0.75 to 1.33).

CONCLUSIONS

Monthly bolus doses of vitamin D supplementation neither enhanced nor hindered cognitive function among older adults. Population-wide vitamin D supplementation of older adults that are largely vitamin D replete is unlikely to substantially benefit cognition.

Efficacy of vitamin D3 supplementation on cancer mortality: systematic review and individual patient data meta-analysis of randomised controlled trials

To evaluate the effect of vitamin D₃ supplementation on cancer mortality in the general population and on prognosis in cancer patients, a systematic review and meta-analysis of randomised, placebo-controlled trials (RCTs) and individual patient data (IPD) was conducted. Overall, 14 RCTs with a total of 104,727 participants (2,015 cancer deaths) were identified and 7 RCTs, including 90% of all study participants (n=94,068), could be included in the IPD meta-analyses. The main meta-analysis of the 14 RCTs yielded a statistically non-significant reduction in cancer mortality by 6% (risk ratio (RR) [95%-confidence interval (95%CI)]: 0.94 [0.86-1.02]). Subgroup analyses revealed a 12% lower cancer mortality in the vitamin D₃ group compared with the placebo group in 10 trials with a daily dosing regimen (RR [95%CI]: 0.88 [0.78-0.98]), whereas no mortality reduction was seen in 4 trials using a bolus regimen (RR [95%CI]: 1.07 [0.91-1.24]; p-value for interaction: 0.042). The IPD meta-analysis (RR [95%CI]: 0.93 [0.84; 1.02]) confirmed the finding of all trials. The IPD were used to test effect modification by age, sex, body mass index, ethnicity, baseline serum 25-hydroxyvitamin D concentration, adherence and cancer-related factors but no statistically significant findings were obtained in meta-analyses of all trials. When restricted to trials with daily dosing in a post-hoc analysis, adults aged ≥70 years (RR [95%CI]: 0.83 [0.77; 0.98]) and subjects with vitamin D₃ therapy initiation before cancer diagnosis (RR [95%CI]: 0.87 [0.69; 0.99]) appeared to benefit most from daily vitamin D₃ supplementation. Measurements of baseline 25-hydroxyvitamin D levels and inclusion of other than non-Hispanic White adults were too sparse in the trials to draw conclusions. Results for all-cause and cancer-specific survival of participants with cancer were comparable to those obtained in the general population for cancer mortality. In conclusion, vitamin D₃ did not reduce cancer mortality in the main meta-analysis of all RCTs because the observed risk reduction by 6% was not statistically significant. However, a subgroup analysis revealed that vitamin D₃ administered daily, in contrast to bolus supplementation, reduced cancer mortality by 12%.

The effects of exposure to solar radiation on human health

This assessment by the Environmental Effects Assessment Panel (EEAP) of the Montreal Protocol under the United Nations Environment Programme (UNEP) evaluates the effects of ultraviolet (UV) radiation on human health within the context of the Montreal Protocol and its Amendments. We assess work published since our last comprehensive assessment in 2018. Over the last four years gains have been made in knowledge of the links between sun exposure and health outcomes, mechanisms, and estimates of disease burden, including economic impacts. Of particular note, there is new information about the way in which exposure to UV radiation modulates the immune system, causing both harms and benefits for health. The burden of skin cancer remains high, with many lives lost to melanoma and many more people treated for keratinocyte cancer, but it has been estimated that the Montreal Protocol will prevent 11 million cases of melanoma and 432 million cases of keratinocyte cancer that would otherwise have occurred in the United States in people born between 1890 and 2100. While the incidence of skin cancer continues to rise, rates have stabilised in younger populations in some countries. Mortality has also plateaued, partly due to the use of systemic therapies for advanced disease. However, these therapies are very expensive, contributing to the extremely high economic burden of skin cancer, and emphasising the importance and comparative cost-effectiveness of prevention. Photodermatoses, inflammatory skin conditions induced by exposure to UV radiation, can have a marked detrimental impact on the quality of life of sufferers. More information is emerging about their potential link with commonly used drugs, particularly anti-hypertensives. The eyes are also harmed by over-exposure to UV radiation. The incidence of cataract and pterygium is continuing to rise, and there is now evidence of a link between intraocular melanoma and sun exposure. It has been estimated that the Montreal Protocol will prevent 63 million cases of cataract that would otherwise have occurred in the United States in people born between 1890 and 2100. Despite the clearly established harms, exposure to UV radiation also has benefits for human health. While the best recognised benefit is production of vitamin D, beneficial effects mediated by factors other than vitamin D are emerging. For both sun exposure and vitamin D, there is increasingly convincing evidence of a positive role in diseases related to immune function, including both autoimmune diseases and infection. With its influence on the intensity of UV radiation and global warming, the Montreal Protocol has, and will have, both direct and indirect effects on human health, potentially changing the balance of the risks and benefits of spending time outdoors.

Guidelines for Preventing and Treating Vitamin D Deficiency: A 2023 Update in Poland

Introduction: All epidemiological studies suggest that vitamin D deficiency is prevalent among the Polish general population. Since vitamin D deficiency was shown to be among the risk factors for many diseases and for all-cause mortality, concern about this problem led us to update the previous Polish recommendations. Methods: After reviewing the epidemiological evidence, case-control studies and randomized control trials (RCTs), a Polish multidisciplinary group formulated questions on the recommendations for prophylaxis and treatment of vitamin D deficiency both for the general population and for the risk groups of patients. The scientific evidence of pleiotropic effects of vitamin D as well as the results of panelists' voting were reviewed and discussed. Thirty-four authors representing different areas of expertise prepared position statements. The consensus group, representing eight Polish/international medical societies and eight national specialist consultants, prepared the final Polish recommendations. Results: Based on networking discussions, the ranges of total serum 25-hydroxyvitamin D concentration indicating vitamin D deficiency [<20 ng/mL (<50 nmol/L)], suboptimal status [20-30 ng/mL (50-75 nmol/L)], and optimal concentration [30-50 ng/mL (75-125 nmol/L)] were confirmed. Practical guidelines for cholecalciferol (vitamin D₃) as the first choice for prophylaxis and treatment of vitamin D deficiency were developed. Calcifediol dosing as the second choice for preventing and treating vitamin D deficiency was introduced. Conclusions: Improving the vitamin D status of the general population and treatment of risk groups of patients must be again announced as healthcare policy to reduce a risk of spectrum of diseases. This paper offers consensus statements on prophylaxis and treatment strategies for vitamin D deficiency in Poland.

Efficacy and Safety of a Personalized Vitamin D3 Loading Dose Followed by Daily 2000 IU in Colorectal Cancer Patients with Vitamin D Insufficiency: Interim Analysis of a Randomized Controlled Trial

A personalized vitamin D3 loading dose has not yet been tested in cancer patients. This interim analysis of the randomized, placebo-controlled VICTORIA trial analyzed the first recruited 74 German adults with nonmetastatic colorectal cancer, a tumor surgery within the past year, and 25-hydroxyvitamin D levels (25(OH)D) < 50 nmol/L. Study participants received a loading dose tailored for a baseline 25(OH)D level and BMI in the first 11 days, followed by a maintenance dose of 2000 IU of vitamin D3 daily until end of trial week 12. The mean 25(OH)D levels were 27.6, 31.0, and 34.1 nmol/L in the placebo group and 25.9, 63.1, and 75.5 nmol/L in the verum group during screening, visit 1 (end of loading dose), and visit 2 (end of maintenance dose), respectively. The prevalence of 25(OH)D) ≥ 50 nmol/L at visits 1 and 2 was 3.5% and 17.4% in the placebo group and 80.0% and 100% in the verum group. No events of 25(OH)D > 150 nmol/L or hypercalcemia were observed. Hypercalciuria events at visit 1 (n = 5 in verum and n = 1 in the placebo group; p = 0.209) receded after discontinuation of the study medication. The personalized loading dose effectively and safely increased the 25(OH)D levels, and 2000 IU of vitamin D3 daily sustained the achieved levels.

Comparing the Evidence from Observational Studies and Randomized Controlled Trials for Nonskeletal Health Effects of Vitamin D

Although observational studies of health outcomes generally suggest beneficial effects with, or following, higher serum 25-hydroxyvitamin D [25(OH)D] concentrations, randomized controlled trials (RCTs) have generally not supported those findings. Here we review results from observational studies and RCTs regarding how vitamin D status affects several nonskeletal health outcomes, including Alzheimer’s disease and dementia, autoimmune diseases, cancers, cardiovascular disease, COVID-19, major depressive disorder, type 2 diabetes, arterial hypertension, all-cause mortality, respiratory tract infections, and pregnancy outcomes. We also consider relevant findings from ecological, Mendelian randomization, and mechanistic studies. Although clear discrepancies exist between findings of observational studies and RCTs on vitamin D and human health benefits these findings should be interpreted cautiously. Bias and confounding are seen in observational studies and vitamin D RCTs have several limitations, largely due to being designed like RCTs of therapeutic drugs, thereby neglecting vitamin D’s being a nutrient with a unique metabolism that requires specific consideration in trial design. Thus, RCTs of vitamin D can fail for several reasons: few participants’ having low baseline 25(OH)D concentrations, relatively small vitamin D doses, participants’ having other sources of vitamin D, and results being analyzed without consideration of achieved 25(OH)D concentrations. Vitamin D status and its relevance for health outcomes can usefully be examined using Hill’s criteria for causality in a biological system from results of observational and other types of studies before further RCTs are considered and those findings would be useful in developing medical and public health policy, as they were for nonsmoking policies. A promising approach for future RCT design is adjustable vitamin D supplementation based on interval serum 25(OH)D concentrations to achieve target 25(OH)D levels suggested by findings from observational studies.

Post-Diagnosis Vitamin D Supplement Use and Survival among Cancer Patients: A Meta-Analysis

Vitamin D administered pre-diagnostically has been shown to reduce mortality. Emerging evidence suggests a role of post-diagnosis vitamin D supplement intake for survival among cancer patients. Thus, we conducted a meta-analysis to evaluate the relationship. PubMed and Embase were searched for relevant observational cohort studies and randomized trials published through April 2022. Summary relative risk (SRR) and 95% confidence interval (CI) were estimated using the DerSimonian–Laird random-effects model. The SRR for post-diagnosis vitamin D supplement use vs. non-use, pooling cohort studies and randomized trials, was 0.87 (95% CI, 0.78–0.98; p = 0.02; I² = 0%) for overall survival, 0.81 (95% CI, 0.62–1.06; p = 0.12; I² = 51%) for progression-free survival, 0.86 (95% CI, 0.72–1.03; p = 0.10; I² = 0%) for cancer-specific survival, and 0.86 (95% CI, 0.64–1.14; p = 0.29; I² = 0%) for relapse. Albeit not significantly heterogeneous by variables tested, a significant inverse association was limited to cohort studies and supplement use during cancer treatment for overall survival, and to studies with ≤3 years of follow-up for progression-free survival. Post-diagnosis vitamin D supplement use was associated with improved overall survival, but not progression-free or cancer-specific survival or relapse. Our findings require confirmation, as randomized trial evidence was insufficient to establish cause-and-effect relationships.