Individual participant data (IPD)-level meta-analysis of randomised controlled trials with vitamin D-fortified foods to estimate Dietary Reference Values for vitamin D.

CONTEXT AND PURPOSE: Individual participant data-level meta-regression (IPD) analysis is superior to meta-regression based on aggregate data in determining Dietary Reference Values (DRV) for vitamin D. Using data from randomized controlled trials (RCTs) with vitamin D3-fortified foods, we undertook an IPD analysis of the response of winter serum 25-hydroxyvitamin (25(OH)D) to total vitamin D intake among children and adults and derived DRV for vitamin D. METHODS: IPD analysis using data from 1429 participants (ages 2-89 years) in 11 RCTs with vitamin D-fortified foods identified via a systematic review and predefined eligibility criteria. Outcome measures were vitamin D DRV estimates across a range of serum 25(OH)D thresholds using unadjusted and adjusted models. RESULTS: Our IPD-derived estimates of vitamin D intakes required to maintain 97.5% of winter 25(OH)D concentrations ≥ 25 and ≥ 30 nmol/L are 6 and 12 µg/day, respectively (unadjusted model). The intake estimates to maintain 90%, 95% and 97.5% of concentrations ≥ 50 nmol/L are 33.4, 57.5 and 92.3 µg/day, respectively (unadjusted) and 17.0, 28.1 and 43.6 µg/day, respectively (adjusted for mean values for baseline serum 25(OH)D, age and BMI). CONCLUSIONS: IPD-derived vitamin D intakes required to maintain 90%, 95% and 97.5% of winter 25(OH)D concentrations ≥ 50 nmol/L are much higher than those derived from standard meta-regression based on aggregate data, due to the inability of the latter to capture between person-variability. Our IPD provides further evidence that using food-based approaches to achieve an intake of 12 µg/day could prevent vitamin D deficiency (i.e., serum 25(OH)D < 30 nmol/L) in the general population.

Effect of Vitamin D Supplementation on Blood Pressure: A Systematic Review and Meta-analysis Incorporating Individual Patient Data.

IMPORTANCE: Low levels of vitamin D are associated with elevated blood pressure (BP) and future cardiovascular events. Whether vitamin D supplementation reduces BP and which patient characteristics predict a response remain unclear. OBJECTIVE: To systematically review whether supplementation with vitamin D or its analogues reduce BP. DATA SOURCES: We searched MEDLINE, CINAHL, EMBASE, Cochrane Central Register of Controlled Trials, and http://www.ClinicalTrials.com augmented by a hand search of references from the included articles and previous reviews. Google was searched for gray literature (ie, material not published in recognized scientific journals). No language restrictions were applied. The search period spanned January 1, 1966, through March 31, 2014. STUDY SELECTION: We included randomized placebo-controlled clinical trials that used vitamin D supplementation for a minimum of 4 weeks for any indication and reported BP data. Studies were included if they used active or inactive forms of vitamin D or vitamin D analogues. Cointerventions were permitted if identical in all treatment arms. DATA EXTRACTION AND SYNTHESIS: We extracted data on baseline demographics, 25-hydroxyvitamin D levels, systolic and diastolic BP (SBP and DBP), and change in BP from baseline to the final follow-up. Individual patient data on age, sex, medication use, diabetes mellitus, baseline and follow-up BP, and 25-hydroxyvitamin D levels were requested from the authors of the included studies. For trial-level data, between-group differences in BP change were combined in a random-effects model. For individual patient data, between-group differences in BP at the final follow up, adjusted for baseline BP, were calculated before combining in a random-effects model. MAIN OUTCOMES AND MEASURES: Difference in SBP and DBP measured in an office setting. RESULTS: We included 46 trials (4541 participants) in the trial-level meta-analysis. Individual patient data were obtained for 27 trials (3092 participants). At the trial level, no effect of vitamin D supplementation was seen on SBP (effect size, 0.0 [95% CI, -0.8 to 0.8] mm Hg; P=.97; I2=21%) or DBP (effect size, -0.1 [95% CI, -0.6 to 0.5] mm Hg; P=.84; I2=20%). Similar results were found analyzing individual patient data for SBP (effect size, -0.5 [95% CI, -1.3 to 0.4] mm Hg; P=.27; I2=0%) and DBP (effect size, 0.2 [95% CI, -0.3 to 0.7] mm Hg; P=.38; I2=0%). Subgroup analysis did not reveal any baseline factor predictive of a better response to therapy. CONCLUSIONS AND RELEVANCE: Vitamin D supplementation is ineffective as an agent for lowering BP and thus should not be used as an antihypertensive agent.

Low iron status as a factor of increased bone resorption and effects of an iron and vitamin D-fortified skimmed milk on bone remodelling in young Spanish women.

PURPOSE: This study aimed to determine whether there is a relationship between iron status and bone metabolism, and to compare the effects of the consumption, as part of the usual diet, of an iron or iron and vitamin D-fortified skimmed milk on bone remodelling in iron-deficient women. METHODS: Young healthy iron-deficient or iron-sufficient women (serum ferritin ≤30 ng/mL or >30 ng/mL, respectively) were recruited. Iron-deficient women were assigned to a nutritional intervention consisting of a randomised, controlled, double-blind, parallel design trial of 16 weeks during winter. They consumed, as part of their usual diet, an iron (Fe group, n = 54) or iron and vitamin D-fortified (Fe+D group, n = 55) flavoured skimmed milk (iron, 15 mg/day; vitamin D3, 5 µg/day, 200 IU). The iron-sufficient women followed their usual diet without supplementation (R group, n = 56). Dietary intake, body weight, iron biomarkers, 25-hydroxyvitamin D (25OHD), parathyroid hormone (PTH), procollagen-type 1 N-terminal propeptide (P1NP), and aminoterminal telopeptide of collagen I (NTx) were determined. RESULTS: Negative correlations were found between baseline log-ferritin and log-NTx (p < 0.001), and between transferrin and P1NP (p = 0.002). Serum 25OHD increased (from 62 ± 21 to 71 ± 21 nmol/L, mean ± SD, p < 0.001) while P1NP and NTx decreased in Fe+D during the assay (p = 0.004 and p < 0.001, respectively). NTx was lower in Fe+D compared to Fe at week 8 (p < 0.05) and was higher in Fe and Fe+D compared to R throughout the assay (p < 0.01). PTH did not show changes. CONCLUSIONS: Iron deficiency is related with higher bone resorption in young women. Consumption of a dairy product that supplies 5 µg/day of vitamin D3 reduces bone turnover and increases circulating 25OHD to nearly reach an optimal vitamin D status, defined as 25OHD over 75 nmol/L.

Changes in blood pressure and lipid levels in young women consuming a vitamin D-fortified skimmed milk: a randomised controlled trial.

UNLABELLED: Vitamin D exerts a variety of extra-skeletal functions. AIM: to know the effects of the consumption of a vitamin D-fortified skimmed milk on glucose, lipid profile, and blood pressure in young women. METHODS: a randomised, placebo-controlled, double-blind parallel-group trial of 16 weeks duration was conducted in young women with low iron stores who consumed a skimmed milk fortified with iron and 200 IU/day (5 µg) of vitamin D (D-fortified group, n = 55), or a placebo without vitamin D (D-placebo group, n = 54). A reference group (n = 56) of iron-sufficient women was also recruited. RESULTS: baseline serum 25-hydroxyvitamin D was inversely correlated with total-cholesterol (r = -0.176, p = 0.023) and low density lipoprotein-cholesterol (LDL-chol) (r = -0.176, p = 0.024). During the assay, LDL-cholesterol increased in the D-placebo group (p = 0.005) while it tended to decrease in the D-fortified group (p = 0.07). Neither group displayed changes in total-cholesterol, high density lipoprotein-cholesterol (HDL-chol), triglycerides or glucose levels. Systolic (p = 0.017) and diastolic (p = 0.010) blood pressure decreased during the assay in the D-fortified group without significant differences compared to the D-placebo. CONCLUSION: consumption of a dairy product fortified with vitamin D reduces systolic and diastolic blood pressure but does not change lipid levels in young women.

Effects of an iron or iron and vitamin D-fortified flavored skim milk on iron metabolism: a randomized controlled double-blind trial in iron-deficient women.

OBJECTIVES: Iron deficiency anemia and vitamin D deficiency are considered global pandemics. The aim of this study was to determine whether the consumption of a dairy product fortified with iron and vitamin D, compared to the equivalent with only added iron, exerts an additional effect on iron metabolism in iron-deficient menstruating women. METHODS: The design was a randomized, placebo-controlled, double-blind, parallel-group trial of 16 weeks' duration. Subjects were randomized into 2 groups that consumed, as part of their usual diet, 500 mL/day of an iron (n = 54) or iron- and vitamin D-fortified (n = 55) flavored skim milk. At baseline and monthly, dietary intake, body weight, and hematological and iron metabolism biomarkers were determined. Serum 25-hydroxyvitamin D was analyzed at baseline and weeks 8 and 16. Data were analyzed by analysis of variance (ANOVA) of repeated measures for time and Time × Group interaction effects. RESULTS: A total of 109 volunteers completed the study. Calcium and iron intakes increased during the intervention (p < 0.001 for both groups). Serum 25-hydroxyvitamin D significantly increased in Fe + D group during the assay (p < 0.001) and at week 16 it was higher compared to the Fe group (p < 0.05). Serum ferritin, serum transferrin, mean corpuscular volume, mean corpuscular hemoglobin, and red blood cell distribution width showed significant time effects but no Time × Group interaction. Higher values of erythrocytes (p = 0.01), hematocrit (p = 0.05), and hemoglobin (p = 0.03) at week 8 were observed in the Fe + D group compared to the Fe group. CONCLUSION: Iron-fortified flavored skim milk does not improve iron status in iron-deficient menstruating women. However, vitamin D fortification slightly enhances erythropoiesis and iron status.

Relationship between vitamin D deficiency, bone remodelling and iron status in iron-deficient young women consuming an iron-fortified food.

BACKGROUND: Iron and vitamin D deficiencies are two of the most widespread nutritional disorders in the world. Our aim was to know whether the consumption of an iron-fortified fruit juice modifies bone remodelling and the possible influence of baseline vitamin D status on the recovery of iron status in a group of iron-deficient women. METHODS: Iron biomarkers, 25-hydroxyvitamin D levels and dietary intake were measured in 123 iron-deficient menstruating women. A subgroup (n = 41) participated in a randomised double-blind placebo-controlled study of 16-weeks during winter. They consumed a placebo fruit juice (P) or iron-fortified fruit juice (F). Dietary intake, 25-hydroxyvitamin D, parathormone (PTH), bone alkaline phosphatase (ALP), aminoterminal telopeptide of collagen I (NTX) and iron biomarkers were determined. RESULTS: Ninety-two per cent of the iron-deficient women were vitamin D deficient or insufficient. Transferrin saturation and 25-hydroxyvitamin D were positively correlated. Iron status improved in F, 25-hydroxyvitamin D decreased in F and P, and PTH, ALP and NTX levels were within the normal range and did not vary. Women with 25-hydroxyvitamin D ≥ 50 nmol/L compared with 25-hydroxyvitamin D < 50 nmol/L showed a higher increase in transferrin saturation (a marker of iron supply to tissues) during iron recovery. CONCLUSION: The prevalence of vitamin D deficiency or insufficiency is very high in iron-deficient women. The recovery of iron status by consuming an iron-fortified food does not affect 25-hydroxyvitamin D levels; however, the increase in iron supply to tissues is lower if the women also present vitamin D deficiency. Although bone health does not seem to be affected in this group of women, correction of iron and vitamin D deficiencies should be promoted in young women to improve present and future health.

Efficacy of a microencapsulated iron pyrophosphate-fortified fruit juice: a randomised, double-blind, placebo-controlled study in Spanish iron-deficient women.

Fe-deficiency anaemia is a worldwide health problem. We studied the influence of consuming an Fe-fortified fruit juice on Fe status in menstruating women. A randomised, double-blind, placebo-controlled study of 16 weeks of duration was performed. Subjects were randomised into two groups: the P group (n 58) or the F group (n 64), and consumed, as a supplement to their usual diet, 500 ml/d of a placebo fruit juice or an Fe-fortified fruit juice, respectively. The Fe-fortified fruit juice, containing microencapsulated iron pyrophosphate, provided 18 mg Fe/d (100 % of the RDA). At baseline and monthly, dietary intake, body weight and Fe parameters were determined: total erythrocytes, haematocrit, mean corpuscular volume (MCV), red blood cell distribution width (RDW), Hb, serum Fe, serum ferritin, serum transferrin, transferrin saturation, soluble transferrin receptor (sTfR) and zinc protoporphyrin (ZnPP). The fruit juice consumption involved increased intake of carbohydrates and vitamin C, and increased BMI within normal limits. Ferritin was higher in the F group after week 4 (P < 0·05) and became 80 % higher than in the P group after week 16 (P < 0·001), and transferrin decreased in the F group compared with the P group after week 4 (P < 0·001). RDW was higher at weeks 4 and 8 in the F group compared with the P group (P < 0·05). Transferrin saturation increased after week 8, and haematocrit, MCV and Hb increased after week 12, in the F group compared with the P group. Serum Fe did not change. sTfR and ZnPP decreased in the F group at week 16 (P < 0·05). Iron pyrophosphate-fortified fruit juice improves Fe status and may be used to prevent Fe-deficiency anaemia.