Background: It is unclear how well surrogate markers for vitamin D exposure (eg, oral intake of vitamin D and estimates of sunlight exposure), with a

The performance of the National Cancer Institute's food frequency questionnaire, the Diet History Questionnaire (DHQ), in estimating servings of 30 US Department of Agriculture Food Guide Pyramid food groups was evaluated in the Eating at America's Table Study (1997–1998), a nationally representative sample of men and women aged 20–79 years. Participants who completed four nonconsecutive, telephone-administered 24-hour dietary recalls (n = 1,301) were mailed a DHQ; 965 respondents completed both the 24-hour dietary recalls and the DHQ. The US Department of Agriculture's Pyramid Servings Database was used to estimate intakes of pyramid servings for both diet assessment tools. The correlation (ρ) between DHQ-reported intake and true intake and the attenuation factor (λ) were estimated using a measurement error model with repeat 24-hour dietary recalls as the reference instrument. Correlations for energy-adjusted pyramid servings of foods ranged from 0.43 (other starchy vegetables) to 0.84 (milk) among women and from 0.42 (eggs) to 0.80 (total dairy food) among men. The mean ρ and λ after energy adjustment were 0.62 and 0.60 for women and 0.63 and 0.66 for men, respectively. This food frequency questionnaire validation study of foods measured in pyramid servings allowed for a measure of food intake consistent with national dietary guidance.

In the past decade, research on the relation between vitamin D exposure and disease in population-based studies has increased exponentially. These studies have involved measurement of vitamin D exposure by means of several methods: blood assays, self-reported dietary and supplemental intakes, and sunlight exposure questionnaires or diaries. As with all exposure measurements, researchers must consider the validity of their assessment tools for capturing vitamin D exposure. The purpose of this article is to summarize our current understanding of the various approaches to measuring vitamin D status within populations as reviewed at the 2007 Experimental Biology symposium, “Assessment of Vitamin D in Population-Based Studies.” In summary, serum 25-hydroxyvitamin D is the accepted biomarker for short-term vitamin D status, but estimates of long-term dietary and supplemental intakes of vitamin D and long-term sunlight exposure may be the most logistically feasible indicators of lifetime vitamin D exposure in population-based studies. Also discussed are issues investigators should consider when analyzing relations between vitamin D exposure and disease outcomes in population-based studies as well as research avenues that need further exploration. The best method for assessing vitamin D status in population-based studies will depend primarily on the research question asked and the critical window of vitamin D exposure hypothesized to be most important.

Background:Vitamin D has anti‐inflammatory and antimicrobial properties that, together with its influence on bone health, may confer periodontal benefit.Methods:Cross‐sectional associations (years 1997‐2000) between plasma 25‐hydroxyvitamin D concentration [25(OH)D] and periodontal measure were investigated among 920 postmenopausal women. Measures of chronic disease were defined based on: 1) alveolar crestal height (ACH) measures from intraoral radiographs and tooth loss and 2) Centers for Disease Control and Prevention (CDC)/American Academy of Periodontology (AAP) criteria using measures of clinical attachment level and probing depth (PD). Acute oral inflammation was assessed by the percentage of gingival sites that bled upon assessment with a probe. Logistic regression was used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) for periodontal disease among participants with adequate [25(OH)D ≥50 nmol/L] compared with deficient/inadequate [25(OH)D <50 nmol/L] vitamin D status adjusted for age, dental visit frequency, and body mass index.Results:No association was observed between vitamin D status and periodontal disease defined by ACH and tooth loss (adjusted OR = 0.96, 95% CI = 0.68 to 1.35). In contrast, women with adequate compared with deficient/inadequate vitamin D status had 33% lower odds (95% CI = 5% to 53%) of periodontal disease according to the CDC/AAP definition and 42% lower odds (95% CI = 21% to 58%) of having ≥50% of gingival sites that bled.Conclusions:Vitamin D status was inversely associated with gingival bleeding, an acute measure of oral health and inflammation, and inversely associated with clinical categories of chronic periodontal disease that incorporated PD, an indicator of oral inflammation. However, vitamin D was not associated with chronic periodontal disease based on measures of ACH in combination with tooth loss.

Vitamin D status has been hypothesized to protect against development of diabetic retinopathy via its anti-inflammatory and anti-angiogenic properties. Additionally, in vitro and in vivo studies suggest vitamin D favorably influences blood pressure and blood glucose control, strong risk factors for diabetic retinopathy. We examined the association between vitamin D status and prevalent diabetic retinopathy in participants with diabetes from a population-based cohort. Among participants in the Atherosclerosis Risk in Communities (ARIC) study with diabetes at visit 3 (1993–1995), 1339 (906 Caucasians, 433 African Americans) had serum 25-hydroxyvitamin (25[OH]D) concentrations assessed at visit 2 (1989–1992) and nonmydriatic retinal photographs taken at visit 3. Dietary intake of vitamin D was assessed at visit 1 (1987–1989). Logistic regression was used to estimate odds ratios (ORs) and 95 % confidence intervals (CIs) for diabetic retinopathy by categories of season-adjusted 25(OH)D (<30 [referent], 30–<50, 50–<75 and ≥75 nmol/L), by quartile of vitamin D intake (IU/day), and use of vitamin D or fish oil supplements (yes/no). P for trend was estimated using continuous 25(OH)D or vitamin D intake. ORs were adjusted for race, and duration of diabetes. We further adjusted for HBA1c and hypertension to examine if 25(OH)D influenced diabetic retinopathy via its effects on either glycemic control or blood pressure. ORs (95 % CIs) for retinopathy, adjusted for race and duration, were 0.77 (0.45–1.32), 0.64 (0.37–1.10), and 0.39 (0.20–0.75), p for trend = 0.001, for participants with 25(OH)D of 30–<50, 50–<75, and ≥75 nmol/L, respectively. Further adjustment for hypertension minimally influenced results (data not show), but adjustment for HBA1c attenuated the OR among those with 25(OH)D ≥75 (0.47 [0.23–0.96], p for trend = 0.030). No statistically significant association was observed between vitamin D intake from foods or supplements and retinopathy. 25(OH)D concentrations ≥75 nmol/L were associated with lower odds of any retinopathy assessed 3 years later. We speculate this may be due in part to vitamin D’s influence on blood glucose control.

Background: Current literature examining associations between vitamin D and chronic disease generally use a single assessment of 25-hydroxyvitamin D [25(OH)D], assuming the 25(OH)D concentration of an individual is consistent over time. Methods: We investigated the intraindividual variability between two measures of plasma 25(OH)D concentrations collected approximately five years apart (1997–2000 to 2002–2005) in 672 postmenopausal women participating in the Women's Health Initiative. Plasma 25(OH)D was assessed using the DiaSorin LIAISON® chemiluminescence immunoassay. The within-pair coefficient of variation (CV) was 4.9% using blinded quality control samples. Mean and SDs of 25(OH)D at the two time points were compared using a paired t test. An intraindividual CV and intraclass correlation coefficient (ICC) were used to assess intraindividual variability. A Spearman correlation coefficient (r) assessed the strength of the association between the two measures, and concordance in vitamin D status at two time points was compared. Results: Mean 25(OH)D concentrations (nmol/L) significantly increased over time from 60.0 (SD = 22.2) to 67.8 (SD = 22.2; P < 0.05). The CV was 24.6%, the ICC [95% confidence interval (CI)] was 0.59 (0.54–0.64), and the Spearman r was 0.61 (95% CI = 0.56–0.66). Greater concordance over five years was observed in participants with sufficient compared with deficient or inadequate baseline 25(OH)D concentrations (weighted kappa = 0.39). Reliability measures were moderately influenced by season of blood draw and vitamin D supplement use. Conclusion: There is moderate intraindividual variation in 25(OH)D concentrations over approximately five years. Impact: These data support the use of a one-time measure of blood 25(OH)D in prospective studies with ≤ five years of follow-up. Cancer Epidemiol Biomarkers Prev; 21(6); 916–24. ©2012 AACR.