Gregory P. Levin

Genetic variants and associations of 25-hydroxyvitamin D concentrations with major clinical outcomes

CONTEXT Lower serum 25-hydroxyvitamin D concentrations are associated with greater risks of many chronic diseases across large, prospective community-based studies. Substrate 25-hydroxyvitamin D must be converted to 1,25-dihydroxyvitamin D for full biological activity, and complex metabolic pathways suggest that interindividual variability in vitamin D metabolism may alter the clinical consequences of measured serum 25-hydroxyvitamin D. OBJECTIVE To investigate whether common variation within genes encoding the vitamin D-binding protein, megalin, cubilin, CYP27B1, CYP24A1, and the vitamin D receptor (VDR) modify associations of low 25-hydroxyvitamin D with major clinical outcomes. DESIGN, SETTING, AND PARTICIPANTS Examination of 141 single-nucleotide polymorphisms in a discovery cohort of 1514 white participants (who were recruited from 4 US regions) from the community-based Cardiovascular Health Study. Participants had serum 25-hydroxyvitamin D measurements in 1992-1993 and were followed up for a median of 11 years (through 2006). Replication meta-analyses were conducted across the independent, community-based US Health, Aging, and Body Composition (n = 922; follow-up: 1998-1999 through 2005), Italian Invecchiare in Chianti (n = 835; follow-up: 1998-2000 through 2006), and Swedish Uppsala Longitudinal Study of Adult Men (n = 970; follow-up: 1991-1995 through 2008) cohort studies. MAIN OUTCOME MEASURE Composite outcome of incident hip facture, myocardial infarction, cancer, and mortality over long-term follow-up. RESULTS Interactions between 5 single-nucleotide polymorphisms and low 25-hydroxyvitamin D concentration were identified in the discovery phase and 1 involving a variant in the VDR gene replicated in independent meta-analysis. Among Cardiovascular Health Study participants, low 25-hydroxyvitamin D concentration was associated with hazard ratios for risk of the composite outcome of 1.40 (95% CI, 1.12-1.74) for those who had 1 minor allele at rs7968585 and 1.82 (95% CI, 1.31-2.54) for those with 2 minor alleles at rs7968585. In contrast, there was no evidence of an association (estimated hazard ratio, 0.93 [95% CI, 0.70-1.24]) among participants who had 0 minor alleles at this single-nucleotide polymorphism. CONCLUSION Known associations of low 25-hydroxyvitamin D with major health outcomes may vary according to common genetic differences in the vitamin D receptor.

Serum 25-Hydroxyvitamin D Concentration and Risk for Major Clinical Disease Events in a Community-Based Population of Older Adults: A Cohort Study

BACKGROUND Circulating concentrations of 25-hydroxyvitamin D [25-(OH)D] are used to define vitamin D deficiency. Current clinical 25-(OH)D targets based on associations with intermediate markers of bone metabolism may not reflect optimal levels for other chronic diseases and do not account for known seasonal variation in 25-(OH)D concentration. OBJECTIVE To evaluate the relationship of 25-(OH)D concentration with the incidence of major clinical disease events that are pathophysiologically relevant to vitamin D. DESIGN Cohort study. SETTING The Cardiovascular Health Study conducted in 4 U.S. communities. Data from 1992 to 2006 were included in this analysis. PARTICIPANTS 1621 white older adults. MEASUREMENTS Serum 25-(OH)D concentration (using a high-performance liquid chromatography-tandem mass spectrometry assay that conforms to National Institute of Standards and Technology reference standards) and associations with time to a composite outcome of incident hip fracture, myocardial infarction, cancer, or death. RESULTS Over a median 11-year follow-up, the composite outcome occurred in 1018 participants (63%). Defining events included 137 hip fractures, 186 myocardial infarctions, 335 incidences of cancer, and 360 deaths. The association of low 25-(OH)D concentration with risk for the composite outcome varied by season (P = 0.057). A concentration lower than a season-specific Z score of -0.54 best discriminated risk for the composite outcome and was associated with a 24% higher risk in adjusted analyses (95% CI, 9% to 42%). Corresponding season-specific 25-(OH)D concentrations were 43, 50, 61, and 55 nmol/L (17, 20, 24, and 22 ng/mL) in winter, spring, summer, and autumn, respectively. LIMITATION The observational study was restricted to white participants. CONCLUSION Threshold concentrations of 25-(OH)D associated with increased risk for relevant clinical disease events center near 50 nmol/L (20 ng/mL). Season-specific targets for 25-(OH)D concentration may be more appropriate than static targets when evaluating health risk. PRIMARY FUNDING SOURCE National Institutes of Health.

Seasonal Variation in 25-Hydroxyvitamin D Concentrations in the Cardiovascular Health Study

Low circulating concentrations of 25-hydroxyvitamin D (25(OH)D) are associated with adverse health outcomes in diverse populations. However, 25(OH)D concentrations vary seasonally with varying exposure to sunlight, so single measurements may poorly reflect long-term 25(OH)D exposure. The authors investigated cyclical trends in average serum 25(OH)D concentrations among 2,298 individuals enrolled in the Cardiovascular Health Study of community-based older adults (1992-1993). A sinusoidal model closely approximated observed 25(OH)D concentrations and fit the data significantly better than did a mean model (P < 0.0001). The mean annual 25(OH)D concentration was 25.1 ng/mL (95% confidence interval: 24.7, 25.5), and the mean peak-trough difference was 9.6 ng/mL (95% confidence interval: 8.5, 10.7). Male sex, higher latitude of study site, and greater physical activity levels were associated with larger peak-trough difference in 25(OH)D concentration (each P < 0.05). Serum concentrations of intact parathyroid hormone and bone-specific alkaline phosphatase also varied in a sinusoidal fashion (P < 0.0001), inversely to 25(OH)D. In conclusion, serum 25(OH)D varies in a sinusoidal manner, with large seasonal differences relative to mean concentration and laboratory evidence of biologic sequelae. Single 25(OH)D measurements might not capture overall vitamin D status, and the extent of misclassification could vary by demographic and behavioral factors. Accounting for collection time may reduce bias in research studies and improve decision-making in clinical care.

Allopurinol and mortality in hyperuricaemic patients

OBJECTIVES While studies have suggested that gout and hyperuricaemia are associated with the risk of premature death, none has investigated the role of urate-lowering therapy on this critical outcome. We examined the impact of allopurinol, the most commonly used urate-lowering drug, on the risk of mortality in hyperuricaemic patients. METHODS From a population of hyperuricaemic veterans of [serum urate level >416 micromol/l (7.0 mg/dl)] at least 40 years of age, we compared the risk of death between incident allopurinol users (n = 2483) and non-users (n = 7441). We estimated the multivariate mortality hazard ratio (HR) of allopurinol use with Cox proportional hazards models. RESULTS Of the 9924 veterans (males, 98% and mean age 62.7 years), 1021 died during the follow-up. Patients who began treatment with allopurinol had worse prognostic factors for mortality, including higher BMI and comorbidities. After adjusting for baseline urate levels, allopurinol treatment was associated with a lower risk of all-cause mortality (HR 0.78; 95% CI 0.67, 0.91). Further adjustment with other prognostic factors did not appreciably alter this estimate (HR 0.77; 95% CI 0.65, 0.91). The mean change from baseline in serum urate within the allopurinol group was -111 micromol/l (-1.86 mg/dl). Adjusting for baseline urate level, allopurinol users had a 40 micromol/l (0.68 mg/dl) lower follow-up serum urate value than controls (95% CI -0.55, -0.81). CONCLUSION Our findings indicate that allopurinol treatment may provide a survival benefit among patients with hyperuricaemia.

Estimating mean annual 25-hydroxyvitamin D concentrations from single measurements: the Multi-Ethnic Study of Atherosclerosis

BACKGROUND The seasonal variation in circulating 25-hydroxyvitamin D [25(OH)D] concentrations is large relative to mean values. Single measurements may misclassify annual exposure, which may lead to bias in research and complicate clinical decision making. OBJECTIVE We aimed to develop and validate a model for adjusting a single measurement of a serum 25(OH)D concentration to the time of year it was measured. DESIGN We measured serum 25(OH)D concentrations by using mass spectrometry in 6476 participants from the Multi-Ethnic Study of Atherosclerosis at baseline and again in a subset of 368 participants at a median of 17 mo later. We estimated a cosinor model to describe the seasonal variability in 25(OH)D concentrations and evaluated this model by using follow-up 25(OH)D measurements. RESULTS The mean age of subjects was 62.1 y, 61.2% of participants were nonwhite, and 53.3% of participants were women. The cosinor model predicted follow-up 25(OH)D concentrations better than a single measurement [difference in root mean squared error (RMSE): 1.3 ng/mL; P< 0.001]. The cosinor model also better predicted the measured annual mean 25(OH)D concentration (difference in RMSE: 1.0 ng/mL; P< 0.001). Annual mean 25(OH)D concentrations estimated from the cosinor model reclassified 7.1% of participants with regard to 25(OH)D deficiency, which was defined as <20 ng/mL. An estimated annual mean 25(OH)D concentration <20 ng/mL was significantly associated with lower bone mineral density, whereas an untransformed 25(OH)D concentration <20 ng/mL was not. CONCLUSIONS Cross-sectional data can be used to estimate subject-specific mean annual 25(OH)D concentrations from single values by using a cosinor model. The tool we developed by using this approach may assist research and clinical care of adults in North America by reducing the misclassification of 25(OH)D deficiency.

Comments on ‘Adaptive increase in sample size when interim results are promising: A practical guide with examples’

In their paper [1], Drs. Mehta and Pocock illustrate the use of a particular approach to revising the maximal sample size of a randomized clinical trial (RCT) by using an interim estimate of the treatment effect. Slightly extending the results of Gao, Ware, and Mehta [2], the authors define conditions on an adaptive rule such that one can know that the naive statistical hypothesis test that ignores the adaptation is conservative. They then use this knowledge to define an adaptive rule for a clinical trial. In our review of this paper, however, we do not find that such an adaptive rule confers any advantage by the usual criteria for clinical trial design. Rather, we find that the designs proposed in this paper are markedly inferior to alternative designs that the authors do not (but should) consider. By way of full disclosure, the first author of this commentary provided to the authors a signed referee’s report on an earlier version of this manuscript, and that report contained the substance (and most of the detail) of this review. In the comments to the editor accompanying that review, the first author described the dilemma that arose during that review. In essence, the methods described in the manuscript do not seem to us worthy of emulation. But on the other hand, the purpose of case studies in the statistical literature is to present an academic exposition of lessons that can be learned. From years of recreational spelunking, we have noted parallels between research and cave exploration. In both processes, explorers spend their time in the dark exploring the maze of potential leads, most often without a clear idea of where they will end up. Because the overwhelming majority of such leads are dead ends, the most useful companions to have along with you are the ones who will willingly explore the dead ends. However, they rapidly become the least useful companions if they have a tendency to explore the dead ends and then come back and tell you the leads went somewhere. Furthermore, the most important skill that any explorers can have is the ability to recognize when they are back at the beginning, lest they believe that the promising lead took them someplace new and become hopelessly lost. According to these criteria, then, the fact that we would not adopt some approach does not necessarily detract from the importance of a paper to the statistical literature. Instead, a paper’s value relates to the extent to which it contributes to our understanding of the methods, which can often be greatly enhanced by identifying dead ends and/or leads that take us back to the beginning. We note that there are several levels to what could be called the “recommended approach” in this paper. At the topmost level, it can be viewed merely as advocating the use of adaptive designs to assess the likelihood of future futility and efficacy of a clinical trial. But in illustrating that use, the authors seem also to advocate for adaptive methods resulting in sampling distributions that are less “heavy tailed” than analogous fixed sample designs (so that they can safely use naive analytic approaches), and they seem to fall prey to some of the difficulties in interpreting conditional power. We note that

An evaluation of inferential procedures for adaptive clinical trial designs with pre‐specified rules for modifying the sample size

Many papers have introduced adaptive clinical trial methods that allow modifications to the sample size based on interim estimates of treatment effect. There has been extensive commentary on type I error control and efficiency considerations, but little research on estimation after an adaptive hypothesis test. We evaluate the reliability and precision of different inferential procedures in the presence of an adaptive design with pre-specified rules for modifying the sampling plan. We extend group sequential orderings of the outcome space based on the stage at stopping, likelihood ratio statistic, and sample mean to the adaptive setting in order to compute median-unbiased point estimates, exact confidence intervals, and P-values uniformly distributed under the null hypothesis. The likelihood ratio ordering is found to average shorter confidence intervals and produce higher probabilities of P-values below important thresholds than alternative approaches. The bias adjusted mean demonstrates the lowest mean squared error among candidate point estimates. A conditional error-based approach in the literature has the benefit of being the only method that accommodates unplanned adaptations. We compare the performance of this and other methods in order to quantify the cost of failing to plan ahead in settings where adaptations could realistically be pre-specified at the design stage. We find the cost to be meaningful for all designs and treatment effects considered, and to be substantial for designs frequently proposed in the literature.

Genetic Variants Modifying the Influence of Vitamin D—Reply

terol effects would be small. Mean monounsaturated fat intake in the United States is 30 g/d and mean unsaturated fat is 46 g/d. Adding 0.8 to 1.6 g/d would be unlikely to have major effects. Potential dose responses for phenolic compounds are not established, and clinical benefits remain speculative. Even so, oleocanthal content in olive oil varies, and even rich sources provide small amounts in only 1 to 2 g/d of olive oil. It is implausible that either oleic acid or other trace compounds in 1 to 2 g/d (0.07-0.14 tablespoons/d) of olive oil would provide meaningful benefits. Furthermore, whereas we used extra virgin olive oil in OPERA, pharmacological placebos in other controlled trials could comprise refined, industry-grade olive oil, containing little phenolic compounds. In addition, completed fish oil trials do not support the idea that use of olive oil as a placebo leads to heterogeneous findings in high vs low olive oil–consuming nations. Both US and Italian trials with olive oil placebos have demonstrated benefits of fish oil. Additionally, in OPERA, nearly half the participants were enrolled from Italy, a subset by itself representing the largest completed trial of fish oil and postoperative atrial fibrillation. Yet the relative risk for fish oil compared with placebo was similar in all 3 countries: 1.01 (95% CI, 0.67-1.52) in the United States, 0.87 (95% CI, 0.54-1.39) in Argentina, and 0.98 (95% CI, 0.72-1.34) in Italy. Cleland and colleagues’ hypothesis cannot explain the negative results of OPERA and other studies. Low-dose olive oil supplements are unlikely to provide meaningful health benefits. The great promise of fish oil—to reduce risk at low intakes—warrants further investigation in well-designed and powered trials.