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

Strategic food vehicles for vitamin D fortification and effects on vitamin D status: A systematic review and meta-analysis of randomised controlled trials

There has been growing interest in the potential of vitamin D food fortification in Europe as a means of addressing low vitamin D status. The WHO-FAO suggest that choosing a suitable food vehicle and ensuring the combination of the food vehicle and the fortificant will be efficacious and effective are of key importance to a successful food fortification programme. Our key objective was to conduct a systematic review and meta-analysis to investigate the effect of various animal- and plant-based food vehicles fortified with vitamin D (as D3 or D2) on circulating 25-hydroxyvitamin D [25(OH)D] concentrations. A list of prioritised food vehicles was established and we searched PubMed, Embase, Scopus and Web of Science for randomised controlled trials (RCTs) which used these vehicles individually, and which met prespecified criteria. The searches identified 49 papers which described suitable RCTs using vitamin D-fortified bread/savoury biscuits (n = 5), orange juice (n = 5), UV-mushrooms (n = 8), cheese (n = 3), yogurt (n = 5), fluid milk (n = 13), powdered milk (n = 5), eggs (n = 2), edible oils (n = 4), or breakfast cereal (n = 1). No suitable RCTs were identified for rice, maize flour, butter, margarine or dairy spreads, plant-based milk or yogurt alternatives. Random-effects meta-analyses of each food vehicle individually indicated weighted mean differences (WMD) in 25(OH)D in the range ∼9-35 nmol/L (3-15 RCT arms, depending on vehicle), and all statistically significant (P < 0.01-0.0001), with the exception of UV-mushrooms (P = 0.06). Heterogeneity was variable (I2 =33-99%, depending on vehicle), but subgroup analysis based on vitamer and dose reduced it in some instances. Sub-group analysis on the basis of whether the food vehicles were from plant-based or animal-based origin showed no significant difference in WMD (15.2 versus 15.9 nmol/L, respectively; P = 0.48). These results support the use of various animal- and plant-based food vehicles for vitamin D fortification to improve circulating 25(OH)D concentrations in populations. This work was registered with PROSPERO as CRD42023439883.

Serum 25-hydroxyvitamin D response to vitamin D supplementation using different lipid delivery systems in middle-aged and older adults: a randomised controlled trial

Food fortification improves vitamin D intakes but is not yet mandated in many countries. Combining vitamin D with different dietary lipids altered vitamin D absorption in in vitro and postprandial studies. This randomised, placebo-controlled trial examined the effect of the lipid composition of a vitamin D-fortified dairy drink on change in 25-hydroxyvitamin D (25(OH)D) concentrations. Sixty-three healthy adults aged 50+ years were randomised to one of the following for 4 weeks: vitamin D-fortified olive oil dairy drink, vitamin D-fortified coconut oil dairy drink, vitamin D supplement or placebo control dairy drink. All vitamin D groups received 20 µg of vitamin D3 daily. Serum was collected at baseline and post-intervention to measure 25(OH)D concentrations and biomarkers of metabolic health. Repeated-measures general linear model ANCOVA (RM GLM ANCOVA) compared changes over time. There was a significant time × treatment interaction effect on 25(OH)D concentrations for those classified as vitamin D-insufficient (P < 0·001) and -sufficient at baseline (P = 0·004). 25(OH)D concentrations increased significantly for all insufficient participants receiving vitamin D3 in any form. However, for vitamin D-sufficient participants at baseline, 25(OH)D concentrations only increased significantly with the coconut oil dairy drink and supplement. There was no effect of vitamin D on biomarkers of metabolic health. Vitamin D fortification of lipid-containing foods may be used in lieu of supplementation when supplement adherence is low or for individuals with dysphagia. These results are important given the recent recommendation to increase vitamin D intakes to 15-20 µg for older adults in Ireland.

Fortification of Staple Foods for Household Use with Vitamin D: An Overview of Systematic Reviews

Vitamin D deficiency is a global public health concern with significant implications for bone health and chronic disease prevention. Our aim was to summarize the evidence from Cochrane and other systematic reviews evaluating the benefits or harms of vitamin D fortification of staple foods for household use. In April 2023, we systematically searched Ovid MEDLINE, Embase, Epistemonikos and the Cochrane Database of Systematic Reviews for systematic reviews investigating the effects of vitamin D fortification of food in general populations of any age. We used Cochrane methodology and assessed the methodological quality of included studies using AMSTAR (A MeaSurement Tool to Assess Systematic Reviews). We assessed the degree of overlap among reviews. All outcomes included in systematic reviews were assessed. The protocol is registered in PROSPERO (registration number: CRD42023420991). We included 27 systematic reviews out of 5028 records for analysis. Overall, 11 out of 12 systematic reviews calculating pooled estimates reported a significant increase in serum 25(OH)D concentrations. The mean change in serum 25(OH)D concentrations per additional 100 units of vitamin D ranged from 0.7 to 10.8 nmol/L. Fortification of food with vitamin D showed a reduction in the prevalence of vitamin D deficiency based on high-certainty evidence. Parathormone (PTH) levels were described to decrease, bone mineral density to increase, while the effects on other bone turnover markers were inconsistent. Fortification did not significantly impact most anthropometric parameters, but it seemed to positively influence lipid profiles. In summary, fortification of food with vitamin D results in a reduction of vitamin D deficiency and might increase serum 25(OH)D concentrations, to varying extents depending on the fortified vehicle and population characteristics. Additionally, fortification may have a positive impact on bone turnover and lipid metabolism but may only have a limited effect on anthropometric parameters.

The effects of vitamin D-fortified foods on circulating 25(OH)D concentrations in adults: a systematic review and meta-analysis

Improvement of vitamin D status of the general population has been a challenge for policymakers. We conducted a meta-analysis to evaluate whether vitamin D-fortified products can be a suitable solution for tackling vitamin D deficiency. Our secondary objective was to determine the effect of some variables including age, latitude and BMI on efficacy of this strategy. MEDLINE, PubMed, Embase, Cochrane Library and Google Scholar were searched and 231 studies were found in a preliminary search. After screening of titles and abstracts, 23 studies were selected. Pooled data comparing fortification with vitamin D +/- Ca with control showed statistically significant effect on total 25(OH)D concentrations (2002 participants, mean difference (MD): 25·4 nmol/l, (95 % CI 19·5, 31·3)). The subgroup analysis by duration of intervention (less than 12 weeks v. more than 12 weeks) and type of vehicle (dairy product, juice, grain product, oil and combination of dairy and grain products), isoform of the vitamin (D₃v. D₂) and dose of the fortificant (≥ 1000 IU/d v. < 1000 IU/d) also indicated significant effect of fortification with vitamin D on serum 25(OH)D concentrations. In conclusion, the circulating 25(OH)D response to vitamin D-fortified food consumption is influenced by age, BMI and the baseline 25(OH)D concentrations. Notwithstanding, an average of 2 nmol/l increase in circulating 25(OH)D concentration for each 100 IU vitamin D intake per d is expected for general adult population. These findings can be informative for policymakers to tackle vitamin D deficiency through food fortification strategy.

Sex and Age Differences Modulate Association of Vitamin D with Serum Triglyceride Levels

The sex and age differences in the relationship between vitamin D and lipid levels remain unclear. This retrospective study investigated the correlations between serum 25-hydroxyvitamin D levels and various biomarkers, along with the sex and age differences in these associations, among 573 men and 436 women during physical check-ups. The mean age of the study population was 51.4 years, and 66% of people had serum 25(OH)D levels below 30 ng/mL. People aged over 65 years had higher 25(OH)D levels than those younger than 65 years, and women had lower 25(OH)D levels than men. Younger age (odds ratio (OR) per year = 1.044, 95% CI, 1.029−1.059, p < 0.0001), female sex (OR = 1.779, 95% CI, 1.149−2.755, p = 0.0097), and elevated serum triglyceride (TG) levels (OR per 1 mg/dL = 1.005, 95% CI, 1.002−1.007, p = 0.0002) were all independent risk factors for vitamin D deficiency. Serum 25(OH)D levels were inversely associated with TG levels. The positive association between vitamin D deficiency and hypertriglyceridemia was significant in men (not in women) and in those aged between 50 and 65 years. In conclusion, younger individuals, women, and middle-aged men with hypertriglyceridemia are at higher risk of vitamin D deficiency.

Using food fortification to improve vitamin D bioaccessibility and intakes

Vitamin D intakes and status are low in many countries due to seasonal UVB exposure variation and the fact that few foods are naturally vitamin D rich. Data modelling studies show that vitamin D intakes increase with food fortification, and countries with mandatory fortification policies have higher vitamin D intakes and status compared to countries without. While many foods can be vitamin D fortified, vitamin D bioavailability differs depending on fortification methods, food structure and composition. Randomised controlled trials (RCT) report that vitamin D2 bioavailability varies between foods, whereas vitamin D3 is bioavailable from many foods. In vitro studies suggest that altering the lipid composition of fortified foods increases vitamin D3 absorption. Olive oil increased vitamin D3 absorption during in vitro digestion compared to other dietary oils. Additionally, when vitamin D3 was incorporated into micelles formed from in vitro digestion of olive oil, more vitamin D3 was absorbed compared to other dietary oils. However, in a human postprandial study, a preformed vitamin D3 micelle dairy drink did not increase vitamin D3 absorption, and a vitamin D3 olive dairy drink increased vitamin D3 absorption in vitamin D insufficient participants only. Action is urgently needed to improve vitamin D intakes and status worldwide. Food fortification improves vitamin D intakes; however, fortification strategies unique to each country are needed. This review will synthesise the literature describing data modelling and intervention trials that assess the safety and efficacy of vitamin D fortification strategies, and those manipulating food composition to alter vitamin D bioavailability from fortified foods. Additionally, RCT examining the impact of vitamin D fortification strategies on vitamin D intakes and status over time are reviewed.

Effect of vitamin D supplementation on markers of cardiometabolic risk in children and adolescents: A meta-analysis of randomized clinical trials

BACKGROUND AND AIMS

An increasing attention to the effect of vitamin D supplementation on cardiometabolic risk markers in children and adolescents has been gained recently. However, the results are inconsistent. Therefore, we conducted a meta-analysis to examine the effect of vitamin D supplementation on cardiometabolic risk markers in children and adolescents.

METHODS AND RESULTS

Eligible randomized controlled trials (RCTs) were identified by searching PubMed, EMBASE and Web of Science. The results of this study are synthetized and reported in accordance with the PRISMA statement. GRADE system was used to assess the certainty of evidence. A total of 9 RCTs were identified and included in the meta-analysis. We found that vitamin D supplementation did not affect the changes of cardiometabolic risk markers including high-density lipoprotein-cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), triglycerides (TG), body mass index (BMI), waist circumferences, systolic blood pressure (SDP) and diastolic blood pressure (DBP). However, vitamin D supplementation showed a beneficial effect on fasting glucose (MD, -1.54 mg/dl, 95% CI -2.98 to -0.10) and TG (MD, -24.76 mg/dl, 95% CI -37.66 to -11.86) in the sub-group analysis of total vitamin D supplementation ≥ 200,000 IU.

CONCLUSIONS

Vitamin D supplementation appeared to have a beneficial effect on reducing fasting glucose and TG level when total vitamin D supplementation ≥200,000 IU but not HDL-C, LDL-C TC, blood pressure and waist circumferences levels in children and adolescents. Further studies are needed to address this issue.

Effect of vitamin D supplementation versus placebo on essential hypertension in patients with vitamin D deficiency: a double-blind randomized clinical trial

Findings from randomized trials addressing the effect of vitamin D supplementation and blood pressure are inconsistent and have been the subject of recent debate. This study aimed to assess the effect of vitamin D supplementation on primary hypertension. This double-blind randomized clinical trial was conducted on patients aged 26-84 years with essential hypertension from March 2017 to April 2019. Patients with vitamin D insufficiency (serum vitamin D levels 20-30 ng/ml) or vitamin D deficiency (serum vitamin D levels <20 ng/ml) were enrolled in the study. Patients were randomly assigned to receive vitamin D supplementation or placebo. Systolic and diastolic blood pressure was measured before the intervention and one and two months thereafter. Of 208 patients enrolled, 171 patients remained for analysis. The effect of vitamin D supplementation on systolic blood pressure was statistically significant in the first and second months after the intervention (P=0.004 and P=0.024, respectively). The effect of vitamin D supplementation on diastolic blood pressure was statistically significant in the first month after the intervention (P=0.046), but not in the second month (P=0.885). No evidence of drug side effects was reported in the two groups. The results of this trial are suggestive of the potential benefits of vitamin D supplementation on blood pressure end points. Therefore, the use of vitamin D may be recommended as an adjuvant drug in the treatment of essential hypertension in patients with vitamin D deficiency because it is safe and well-tolerated by the patients and can significantly reduce the systolic and diastolic blood pressure. Trial registration: Iranian Registry of Clinical Trials registration number: IRCT201703129014N151.

Efficacy and safety of food fortification to improve vitamin D intakes of older adults

OBJECTIVES

The aim of this study was to determine the best foods for potential vitamin D food fortification and to model the efficacy and safety of different food fortification scenarios in adults ≥50 y of age in Ireland.

METHODS

National Adult Nutrition Survey vitamin D data for participants ≥50 y of age were updated. Vitamin D from foods with natural and added vitamin D was estimated and daily vitamin D intake patterns were examined. Data modeling was used to estimate the effects of target food fortification scenarios.

RESULTS

Almost two-thirds of the mean daily vitamin D intake of adults ≥50 y of age (7 ± 7 µg) comes from foods with added vitamin D. Milk and bread are the most frequently consumed foods across all meals and were subsequently targeted for the data modeling exercise. Results from the data modeling show that vitamin D intake increased between 9 and 17 µg/d, depending on the fortification scenario. Fortifying milk or bread resulted in ∼30% or ∼55% of individuals meeting the Recommended Daily Allowance (RDA); however, fortifying both simultaneously resulted in ∼70% meeting the RDA.

CONCLUSIONS

Currently, the majority of Irish adults ≥50 y of age are not meeting dietary recommendations for vitamin D. Fortification of commonly consumed foods such as milk and bread could improve daily intakes such that ∼70% of the cohort would meet the minimum recommendation. Future research should examine the efficacy of different food fortification scenarios to improve vitamin D intakes for older adults.

Determination and Analysis of Trace Elements in Five Kinds of Traditional Chinese Medicine in High Blood Pressure Medicinal Food by ICP-AES

Objective. To establish a method for analysis of microelements in five kinds of traditional Chinese medicine in high blood pressure medicinal food, mainly including manganese, cobalt, selenium, iron, magnesium, and other 15 elements. Methods. The samples were digested using a microwave digestion instrument through NHO3-H2O2 solution, and then, the elements were synthesized by inductively coupled plasma atomic emission spectrometry (ICP-AES). Results. The content of cobalt, manganese, zinc, copper, and nickel in the high blood pressure diet foods is higher, the RSD is between 0.005% and 4.82%, and the recovery rate ranges from 93.40% to 106.5%. The precision and recovery of the detection method are higher. Conclusion. The experiment result is better. Medicinal foods curing high blood pressure contain a number of micronutrients that are beneficial to the human body. This experiment provides some meaningful basis for the prevention and treatment of cardiovascular diseases such as hypertension.

Effect of Vitamin D on Blood Pressure and Hypertension in the General Population: An Update Meta-Analysis of Cohort Studies and Randomized Controlled Trials

Background

The effect of vitamin D supplementation on blood pressure has been explored in previous meta-analyses, but whether the association is causal in the general population is still unknown. We evaluated the association comprehensively and quantitatively.

Methods

We searched PubMed and Embase for relevant cohort studies and randomized controlled trials (RCTs). We used a 2-step generalized least-squares method to assess the dose–response association of circulating 25-hydroxyvitamin D (25[OH]D) and hypertension and a fixed-effects model to pool the weighted mean differences (WMDs) and corresponding 95% confidence intervals (95% CIs) of blood pressure across RCTs.

Results

We identified 11 cohort studies and 27 RCTs, with 43,320 and 3,810 participants, respectively. The dose–response relationship between circulating 25(OH)D levels and hypertension risk was approximately L-shaped (P_nonlinearity = .04), suggesting that the risk of hypertension increased substantially below 75 nmol/L as 25(OH)D decreased, but it remained significant over the range of 75–130 nmol/L. However, pooled results of RCTs showed that there was no significant reduction in systolic blood pressure (WMD, −0.00 mm Hg; 95% CI, −0.71 to 0.71) or diastolic blood pressure (WMD, 0.19 mm Hg; 95% CI, −0.29 to 0.67) after vitamin D intervention.

Conclusions

The results of this meta-analysis indicate that supplementation with vitamin D does not lower blood pressure in the general population. RCTs with long-term interventions and a sufficient number of participants who have low levels of vitamin D are needed to validate these findings.

Extra-Skeletal Effects of Vitamin D

The vitamin D receptor is expressed in multiple cells of the body (other than osteoblasts), including beta cells and cells involved in immune modulation (such as mononuclear cells, and activated T and B lymphocytes), and most organs in the body including the brain, heart, skin, gonads, prostate, breast, and gut. Consequently, the extra-skeletal impact of vitamin D deficiency has been an active area of research. While epidemiological and case-control studies have often suggested a link between vitamin D deficiency and conditions such as type 1 and type 2 diabetes, connective tissue disorders, inflammatory bowel disorders, chronic hepatitis, food allergies, asthma and respiratory infections, and cancer, interventional studies for the most part have failed to confirm a causative link. This review examines available evidence to date for the extra-skeletal effects of vitamin D deficiency, with a focus on randomized controlled trials and meta-analyses.

Vitamin D and Hypertension

Vitamin D has the pleiotropic effects in multiple organ systems, and vitamin D deficiency was suggested to be associated with high blood pressure according to previous reports. Several interventional studies have examined the effect of vitamin D supplementation on high blood pressure patients, but the results have been inconsistent. In this article, we examined the literature that have proposed a mechanism involving vitamin D in the regulation of blood pressure and review previous observational and interventional studies that have shown the relationship between vitamin D and hypertension among various populations.

Seasonal variations of vitamin D and its relation to lipid profile in Iranian children and adults

BACKGROUND

Vitamin D has a multitude of functional properties and acts like a hormone in the body. Its effect on the lipid profile is one of the proposed mechanisms for its relationship with many disorders during its deficiency. But, this relationship is still conflicting and debatable, so this study was conducted to determine the association between serum level of vitamin D and lipid profiles, including serum concentrations of cholesterol, triglyceride (TG), HDL, and LDL in healthy subjects.

METHODS

In this cross-sectional study, 541 volunteers with age of 5-60 years from normal and healthy subjects were selected via random sampling. Demographics and history of daily or weekly sunlight exposures were recorded. Measuring vitamin D was done in two consecutive seasons: winter and summer. Ten milliliters of peripheral venous blood sample was withdrawn after an overnight fasting. Serum levels of 25(OH) D (25, hydroxy vitamin D3) were measured using the enzyme-linked immunosorbent assay (ELISA), and the Confirmatory test was done by high-performance liquid chromatography (HPLC).

RESULTS

Mean age in the total mixed population was 30.83 ± 14.02 years. Subjects were 50.5% male and 49.5% female. Mean 25(OH) D in the total population for winter and summer were 45.8 ± 24.26 ng/ml and 55.24 ± 37.47 ng/ml respectively. In the total population, 38.08% were vitamin D deficient. Comparing serum lipid levels in the summer and winter showed a significant difference for cholesterol, LDL, and HDL, but no significant effect was found for TG. Analysis for the comparison of lipid profiles between the two genders in winter showed that there were significant differences in all lipid profiles except for LDL, while such analysis for summer revealed significant difference just for TG. In multivariate analysis, there was a significant mean difference only for LDL in subgroups with vitamin D insufficiency and deficiency. There was no correlation between Vitamin D and lipid profiles.

CONCLUSIONS

Vitamin D is different between the two seasons regardless of gender variations. Its status showed some significant relationship with some lipid profiles (cholesterol, LDL, and HDL) during the two seasons. There were different results among winter and summer based on the gender.

Discrepant association of serum C-3 epimer of 25-hydroxyvitamin D versus non-epimeric 25-hydroxyvitamin D with serum lipid levels

Background

Low vitamin D status has been associated with a number of chronic diseases. For dyslipidemia, vitamin D deficiency has been associated with higher low density lipoprotein-cholesterol (LDL-C) in a number of studies, but with inconsistent results in clinical trials. The purpose of the present study is to explore the relative importance of 3-epi-25-hydroxyvitamin D (25(OH)D) as compared with the non-epimeric form in relation to serum lipid.

Method

This study used data from 1068 randomly selected volunteers in the Thai 4^th National Health Examination Survey (NHES IV). Serum 25(OH)D₂, 25(OH)D₃, 3-epi-25(OH)D₂ and 3-epi-25(OH)D₃ were analyzed by liquid chromatography–tandem mass spectrometry.

Results

There was no association between serum total 25(OH)D and serum LDL-C. However, circulating 3-epi-25(OH)D₃ was negatively related to serum LDL-C (r = −0.077, P <0.05), while no such association was found for non-epimeric 25(OH)D₃ (r =0.030, P = 0.33). On the other hand, both 3-epi-25(OH)D₃ (r = 0.175, P <0.001) and non-epimeric 25(OH)D₃ (r = 0.142, P <0.001) were positively related to serum triglyceride (TRIG) levels. In multiple linear regression models with age, gender, body mass index , urban residence, education, hypertension and education as covariates, it was found that 3-epi-25(OH)D₃ was independently associated with serum LDL-C (beta = −0.12, P <0.01), while non-epimeric 25(OH)D₃ was positively related to LDL-C (beta = 0.13, P = 0.002). For TRIG, there were positive association with 3-epi-25(OH)D₃ (beta = 0.27, P <0.001) and negative association with non-epimeric 25(OH)D₃ (beta = − 0.10, P = 0.011) independent of age, gender, urban resident and education.

Conclusions

There is a discrepant association of 25(OH)D levels with serum lipids according to 25(OH)D epimeric forms.

Development of albuminuria and enhancement of oxidative stress during chronic renin-angiotensin system suppression

OBJECTIVE

Albuminuria has been recently described in hypertensive patients under chronic renin-angiotensin system (RAS) suppression. We investigated whether this fact could be related to an increase in oxidative stress.

METHODS

We examined normoalbuminuric and albuminuric patients in stage 2 chronic kidney disease, both with more than 2 years of RAS blockade. The relationship between albuminuria and circulating biomarkers for both oxidative damage, that is carbonyl and malondialdehyde, as well as antioxidant defense, that is reduced glutathione, thiol groups, uric acid, bilirubin, or catalase, and superoxide scavenging activity, was assessed.

RESULTS

We found that only patients with albuminuria showed an important increase in carbonyls (P < 0.001) and malondialdehyde (P < 0.05) compared to normoalbuminuric patients. This increase in oxidative damage was also accompanied by a rise in catalase activity (P < 0.05) and low-molecular-weight antioxidants only when they were measured as total antioxidant capacity (P < 0.01). In order to establish the specific oxidative status of each group, new indexes of oxidative damage and antioxidant defense were calculated with all these markers following a mathematical and statistical approach. Although both pro-oxidant and antioxidant indexes were significantly increased in patients with albuminuria, only the oxidative damage index positively correlated with the increase of albumin/creatinine ratio (P = 0.0024).

CONCLUSIONS

We conclude that albuminuria is accompanied by an amplified oxidative damage in patients in early stages of chronic kidney disease. These results indicate that chronic RAS protection must be directed to avoid development of albuminuria and oxidative damage.

Age and sex differences in the relationship between serum 25-hydroxyvitamin D and hypertension in the general Korean population

BACKGROUND/OBJECTIVES

Previous studies have suggested that serum 25-hydroxyvitamin D (25(OH)D) is associated with hypertension. However, the effects of age and sex on the relation between serum 25(OH)D and hypertension has not been examined. The present study examined the relationship between serum 25(OH)D and hypertension by age and sex in the general Korean population, considering potential confounders for hypertension.

SUBJECTS/METHODS

We conducted a population-based, cross-sectional study. Twenty thousand four hundred and forty adults aged 19 years or older, who participated in the 2009-2012 Korean National Health and Nutrition Examination Surveys, were selected for the present study. Hypertension was defined as a systolic blood pressure ⩾ 140 mm Hg, diastolic blood pressure ⩾ 90 mm Hg or current use of antihypertensive medication.

RESULTS

We found that serum 25(OH)D levels are inversely associated with hypertension in young and middle-aged adults, but not in the elderly population. In young and middle-aged adults, the adjusted odds ratios (ORs) for hypertension tended to decrease according to the quartiles of serum 25(OH)D after adjustment for potential confounders, although it was only significant in women (OR=0.73, 95% confidence interval (CI)=0.58-0.91, P for trend=0.0349). There was no association between serum 25(OH)D concentration and hypertension in elderly subjects of either sex.

CONCLUSIONS

A higher serum 25(OH)D level was strongly associated with a lower prevalence of hypertension in young and middle-aged Korean women, but not in elderly adults.

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.

Determinants of vitamin D deficiency among undergraduate medical students in Saudi Arabia

BACKGROUND/OBJECTIVES

The objectives of our study were to determine possible factors associated with low vitamin D levels in medical students.

SUBJECTS/METHODS

A cross-sectional study was performed among 255 first- to fifth-year male undergraduate medical students of one of the major universities in Saudi Arabia. Serum 25-hydroxyvitamin D (25(OH)D) levels were measured using electrochemiluminiscence. Multiple logistic regression analysis was performed.

RESULTS

Majority of Saudi medical students (75.2%) had 25(OH)D levels <30 nmol/l, defined as risk for deficiency by the Institute of Medicine. Multivariate analysis showed that the odds of having 25(OH)D serum levels of ⩾ 30 nmol/l were seven times higher both in students who took vitamin D (odds ratio (OR)=7.2, 95% confidence interval (CI)=1.8-29.9, P=0.006) or multivitamin supplements (OR=6.9, 95% CI=1.7-27.3, P=0.006) within 1 year. Students with a history of vitamin D testing >1 year before the study or moderate/vigorous physical activity (PA) had 4.4 (OR=4.4, 95% CI=1.7-11.4, P=0.003) and 2.7-fold (OR=2.7, 95% CI=1.3-5.3, P=0.006) higher odds of having 25(OH)D levels ⩾ 30 nmol/l, respectively. There was no significant association between 25(OH)D serum levels and average time spent outdoors per day (P=0.369) and type of clothing (long-sleeved vs short-sleeved; P=0.800).

CONCLUSIONS

Vitamin D deficiency was highly prevalent in Saudi medical students. Modifiable factors such as vitamin D intake and PA could be targeted for intervention. Further studies with standardized laboratory measurements of 25(OH)D are needed to explore the role of vitamin D testing in behavioral change, which may lead to increased serum 25(OH)D levels.