Vitamin D deficiency in infants is widely prevalent. Most paediatric professional associations recommend routine vitamin D prophylaxis for infants. However, the optimal dose and duration of supplementation are still debated. We aimed to compare the efficacy and safety of different vitamin D supplementation regimens in term and late preterm neonates. For this systematic review and network meta-analysis, we searched MEDLINE, the Cochrane Central Register of Controlled Trials and Embase. Randomised and quasi-randomised clinical trials that evaluated any enteral vitamin D supplementation regimen initiated within 6 weeks of life were included. Two researchers independently extracted data on study characteristics and outcomes and assessed quality of included studies. A network meta-analysis with a Bayesian random-effects model was used for data synthesis. Certainty of evidence (CoE) was assessed using GRADE. Primary outcomes were mean serum vitamin D concentrations and the proportion of infants with vitamin D insufficiency (VDI). We included twenty-nine trials that evaluated fourteen different regimens of vitamin D supplementation. While all dosage regimens of ≥400 IU/d increased the mean 25(OH)D levels compared with no treatment, supplementation of ≤250 IU/d and 1400 IU/week did not. The CoE varied from very low to high. Low CoE indicated that 1600 IU/d, compared with lower dosages, reduced the proportion of infants with VDI. However, our results indicated that any dosage of ≥800 IU/d increased the risk of hypervitaminosis D and hypercalcaemia. Data on major clinical outcomes were sparse. Vitamin D supplementation of 400–600 IU/d may be the most effective and safest in infants.

Insufficiency of vitamin D, during pregnancy, is a common cause of various pregnancy-related complications. Despite such insufficiency being frequently reported among South Asian pregnant women, the absence of systematic review and meta-analysis renders the true extent of this problem being poorly characterised. In this systematic review, three main databases (PubMed, Scopus and Google Scholar) were searched for original studies. We included original studies published between 1January 2001 to 31 December 2019, conducted on pregnant women who lived in South Asian countries and reported the prevalence of vitamin D insufficiency among the study participants. Twenty studies with a total of 7804 participants from four South Asian countries finally met our selection criteria. Overall pooled prevalence of insufficiency was 65 % (95 % CI: 51 %, 78 %) with a significant heterogeneity (I2 = 99·37 %; P = 0·00). The average level of vitamin D ranged from 9 ng/ml to 24·86 ng/ml with a weighted mean of 16·37 ng/ml (weighted standard deviation 7·13 ng/ml). The highest prevalence of insufficiency was found in Pakistan (76 %) followed by India (67 %), Bangladesh (64 %) and Nepal (14 %). Results obtained in this study suggest that vitamin D insufficiency is highly prevalent among South Asian pregnant women. Being the first systematic review in this region, findings from this study will help the future studies and strengthen the evidence for policymakers to develop effective mitigation strategies.

Vitamin D deficiency (VDD) and insufficiency (VDI) are increasing at a global level, and they are associated with increased risk of various diseases. However, little information is available on the prevalence and predictors of VDD and VDI in a representative population of US adults. Serum 25-hydroxyvitamin D (25(OH)D) measurements were collected from 26 010 adults aged ≥18 years from the National Health and Nutrition Examination Survey (NHANES) 2001–2010. Using thresholds recommended by the Endocrine Society, VDD was defined as 25(OH)D<50 nmol/l and VDI as 50≤25(OH)D<75 nmol/l. Weighted multinomial log-binomial regression was conducted to estimate prevalence ratios of VDD and VDI. The prevalences of VDD and VDI in 2001–2010 were 28·9 and 41·4 %, respectively. Adults who were black, less educated, poor, obese, current smokers, physically inactive and infrequent milk consumers had a higher prevalence of VDD. After adjustment for other potential predictors, obese adults showed 3·09 times higher prevalence of VDD and 1·80 times higher prevalence of VDI than non-obese adults. Physically inactive adults had 2·00 and 1·36 times higher prevalence of VDD and VDI than active peers. Compared with frequent consumers, rare consumers of milk had 2·44 and 1·25 times higher prevalence of VDD and VDI, respectively. Current alcohol drinkers had 38 % lower prevalence of VDD than non-drinkers. Awareness of the high prevalence of VDD and VDI among US adults and related predictors could inform behavioural and dietary strategies for preventing VDD and monitoring VDI, especially in old, black, obese and inactive individuals who report rare consumption of milk.

Maternal vitamin D insufficiency is associated with childhood rickets and longer-term problems including schizophrenia and type 1 diabetes. Whilst maternal vitamin D insufficiency is common in mothers with highly pigmented skin, little is known about vitamin D status of Caucasian pregnant women. The aim was to investigate vitamin D status in healthy Caucasian pregnant women and a group of age-matched non-pregnant controls living at 54–55°N. In a longitudinal study, plasma 25-hydroxyvitamin D (25(OH)D) was assessed in ninety-nine pregnant women at 12, 20 and 35 weeks of gestation, and in thirty-eight non-pregnant women sampled concurrently. Plasma 25(OH)D concentrations were lower in pregnant women compared to non-pregnant women (P < 0·0001). Of the pregnant women, 35, 44 and 16 % were classified as vitamin D deficient (25(OH)D < 25 nmol/l), and 96, 96 and 75 % were classified as vitamin D insufficient (25(OH)D < 50 nmol/l) at 12, 20 and 35 weeks gestation, respectively. Vitamin D status was higher in pregnant women who reported taking multivitamin supplements at 12 (P < 0·0001), 20 (P = 0·001) and 35 (P = 0·001) weeks gestation than in non-supplement users. Vitamin D insufficiency is evident in pregnant women living at 54–55°N. Women reporting use of vitamin D-containing supplements had higher vitamin D status, however, vitamin D insufficiency was still evident even in the face of supplement use. Given the potential consequences of hypovitaminosis D on health outcomes, vitamin D supplementation, perhaps at higher doses than currently available, is needed to improve maternal vitamin D nutriture.

Despite recent concerns about the high prevalence of sub-clinical vitamin D deficiency in adolescents, relatively few studies have investigated the underlying reasons. The objective of the present study was to investigate the prevalence and predictors of vitamin D inadequacy among a large representative sample of adolescents living in Northern Ireland (54–55°N). Serum concentrations of 25-hydroxyvitamin D (25(OH)D) were analysed by enzyme-immunoassay in a subgroup of 1015 of the Northern Ireland Young Hearts 2000 cohort; a cross-sectional study of 12 and 15 year-old boys and girls. Overall mean 25(OH)D concentration throughout the year was 64·3 (range 5–174) nmol/l; 56·7 and 78·1 nmol/l during winter and summer, respectively. Reported intakes of vitamin D were very low (median 1·7 μg/d). Of those adolescents studied, 3 % and 36 % were vitamin D deficient and inadequate respectively, as defined by serum 25(OH)D concentrations < 25 and < 50 nmol/l. Of the subjects, 46 % and 17 % had vitamin D inadequacy during winter and summer respectively. Gender differences were also evident with 38 % and 55 % of boys and girls respectively classified as vitamin D inadequate during winter (P < 0·001). Predictors of vitamin D inadequacy during winter were vitamin D intake and gender. In conclusion, there is a high prevalence of vitamin D inadequacy in white-skinned adolescents in Northern Ireland, particularly during wintertime and most evident in girls. There is a clear need for dietary recommendations for vitamin D in this age group and for creative strategies to increase overall vitamin D status in the population.

Vitamin D is metabolised by a hepatic 25-hydroxylase into 25-hydroxyvitamin D (25(OH)D) and by a renal 1α-hydroxylase into the vitamin D hormone calcitriol. Calcitriol receptors are present in more than thirty different tissues. Apart from the kidney, several tissues also possess the enzyme 1α-hydroxylase, which is able to use circulating 25(OH)D as a substrate. Serum levels of 25(OH)D are the best indicator to assess vitamin D deficiency, insufficiency, hypovitaminosis, adequacy, and toxicity. European children and young adults often have circulating 25(OH)D levels in the insufficiency range during wintertime. Elderly subjects have mean 25(OH)D levels in the insufficiency range throughout the year. In institutionalized subjects 25(OH)D levels are often in the deficiency range. There is now general agreement that a low vitamin D status is involved in the pathogenesis of osteoporosis. Moreover, vitamin D insufficiency can lead to a disturbed muscle function. Epidemiological data also indicate a low vitamin D status in tuberculosis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel diseases, hypertension, and specific types of cancer. Some intervention trials have demonstrated that supplementation with vitamin D or its metabolites is able: (i) to reduce blood pressure in hypertensive patients; (ii) to improve blood glucose levels in diabetics; (iii) to improve symptoms of rheumatoid arthritis and multiple sclerosis. The oral dose necessary to achieve adequate serum 25(OH)D levels is probably much higher than the current recommendations of 5–15 μg/d.