Seasonal changes in Vitamin D-effective UVB availability in Europe and associations with population serum 25-Hydroxyvitamin D

Low vitamin D status is common in Europe. The major source of vitamin D in humans is ultraviolet B (UVB)-induced dermal synthesis of cholecalciferol, whereas food sources are believed to play a lesser role. Our objectives were to assess UVB availability (Jm−2) across several European locations ranging from 35° N to 69° N, and compare these UVB data with representative population serum 25-hydroxyvitamin D (25(OH)D) data from Ireland (51–54° N), Iceland (64° N) and Norway (69° N), as exemplars. Vitamin D-effective UVB availability was modelled for nine European countries/regions using a validated UV irradiance model. Standardized serum 25(OH)D data was accessed from the EC-funded ODIN project. The results showed that UVB availability decreased with increasing latitude (from 35° N to 69° N), while all locations exhibited significant seasonal variation in UVB. The UVB data suggested that the duration of vitamin D winters ranged from none (at 35° N) to eight months (at 69° N). The large seasonal fluctuations in serum 25(OH)D in Irish adults was much dampened in Norwegian and Icelandic adults, despite considerably lower UVB availability at these northern latitudes but with much higher vitamin D intakes. In conclusion, increasing the vitamin D intake can ameliorate the impact of low UVB availability on serum 25(OH)D status in Europe.

The relationship between 25-hydroxyvitamin D concentration in early pregnancy and pregnancy outcomes in a large, prospective cohort

Vitamin D insufficiency and deficiency have been associated with an increased risk of adverse pregnancy outcomes. Controversy remains as findings have been inconsistent between disparate populations. The aim of this study was to investigate the relationship between vitamin D status and pregnancy outcomes in a large, prospective pregnancy cohort. 25-Hydroxyvitamin D concentration was analysed in serum samples collected at 15 weeks of gestation from 1710 New Zealand women participating in a large, observational study. Associations between vitamin D status and pre-eclampsia, preterm birth, small for gestational age (SGA) and gestational diabetes were investigated. The mean 25-hydroxyvitamin D concentration was 72·9 nmol/l. In all, 23 % had 25-hydroxyvitamin D concentrations <50 nmol/l, and 5 % of participants had concentrations <25 nmol/l. Women with 25-hydroxyvitamin D concentrations <75 nmol/l at 15 weeks of gestation were more likely to develop gestational diabetes mellitus than those with concentrations >75 nmol/l (OR 2·3; 95 % CI 1·1, 5·1). However, this effect was not significant when adjustments were made for BMI and ethnicity (OR 1·8; 95 % CI 0·8, 4·2). 25-Hydroxyvitamin D concentration at 15 weeks was not associated with development of pre-eclampsia, spontaneous preterm birth or SGA infants. Pregnancy complications were low in this largely vitamin D-replete population.

Vitamin D status and requirements during pregnancy and lactation

Vitamin D deficiency during pregnancy, lactation, and early infancy has been widely reported. Current understanding of vitamin D metabolism during pregnancy and lactation is incomplete, and to date, experimental data to support vitamin D requirements for these life stages are scarce. There is a shortage of nationally representative data and appropriate reference ranges for serum 25-hydroxyvitamin D (25OHD) during pregnancy, lactation and infancy, including in umbilical cord blood. This thesis described concentrations of total 25OHD and individual metabolites including 25OHD3, 25OHD2, and 3-epi-25OHD3 at 15 weeks’ gestation in a large seasonally balanced pregnancy cohort study (n 1768), carried out in Cork, Ireland (52oN). The prevalence of low 25OHD concentrations in pregnant women was higher than published reports in other Caucasian women, and was highest among non-users of vitamin D-containing supplements during winter. A longitudinal pregnancy study was included which suggested gestational stages had an impact on the total serum 25OHD concentration. This thesis incorporated a randomized controlled trial carried out among 100 women across 3 intervention groups using 20 μg/day of vitamin D3 with or without 500 mg calcium, or placebo, over 12-weeks of lactation to investigate the vitamin D requirement for lactating mothers and the vitamin D content of human milk. A daily intake of 25 μg/day was suggested to meet the requirement of lactating women to maintain a 25OHD levels above 50 nmol/L in 97.5% of the population at 52oN all year around. However, vitamin D content in human milk did not increase in response to supplementation. Serum 25OHD concentration has been used as a predictor of a number of health outcomes. This thesis reported large differences in serum 25OHD concentrations using different methods in 86 umbilical cord samples. The need for international standardization of serum 25OHD measurements was re-emphasized in this thesis.

Early nutrition and eczema in infancy

Eczema prevalence rates among Irish infants are unreported, despite eczema being the most common inflammatory condition of infancy. Maternal and infant nutritional status including vitamin D and other fat-soluble vitamins as well as early infant feeding have been linked with eczema initiation and development. Therefore, early nutrition could be a potential modifiable risk factor. The objective of this thesis was to prospectively describe early infant feeding and complementary feeding practices, to evaluate infant vitamin D supplementation practice, to quantify cord serum 25-hydroxyvitamin D [25(OH)D] and propose reference intervals for vitamin D metabolites, to report eczema prevalence and explore the potential role of infant nutrition and eczema. These research needs were investigated through the Cork BASELINE (Babies After SCOPE: Evaluating the Longitudinal Impact with Neurological and Nutritional Endpoints) Birth Cohort Study (n 2137). This thesis was the first comprehensive report from the birth cohort, therefore it was important to describe the cohort sociodemographic profile. Although socio-demographic characteristics compared well with national data, there was an over-representation of educated mothers which may limit the generalizability of the results. From August 2008 through November 2011, comprehensive postnatal assessments were completed at day 2 and at 2, 6, 12 and 24 months. Breastfeeding rates were low, while complementary feeding practices were broadly compliant with national guidelines. The implementation of a national infant vitamin D supplementation policy had a major impact on supplementation practice. Low levels of serum 25(OH)D were universal among Irish neonates. Eczema is a complex and multifaceted disease, which is increasing globally. This was the first report of eczema prevalence data among Irish infants which compared with international reports. Given the high prevalence and considerable burden eczema has on the lives of sufferers, intensive research efforts to identify a cause and therapeutic strategies to prevent/reduce eczema was re-emphasized in this thesis.

Nutrition, growth and body composition in infancy

This thesis is presented in two parts. Data for this research is from the Cork BASELINE (Babies after SCOPE, Evaluating Longitudinal Impact using Neurological and Nutritional Endpoints) Birth Cohort Study (n = 2137). In this prospective birth cohort study, pediatric follow-up with in-person appointments were repeated from the time of birth through to 2, 6 and 12 months, and at 2 years. Body composition was measured by air displacement plethysmography at birth and at 2 months using the PEA POD Infant Body Composition Tracking System. This thesis provides the first extensive report on the study’s 2 year assessment. In part one, the aims were to investigate potential early-life risk factors for childhood overweight and obesity, including rapid growth and body composition in infancy and umbilical cord concentrations of leptin and high molecular weight (HMW) adiponectin. This research is the first to describe rapid growth in early infancy in terms of changes in direct measures of body composition. These are also the first data to examine associations between umbilical cord leptin and HMW adiponectin concentrations and changes in fat and lean mass in early infancy. These data provide additional insight into characterising the growth trajectory in infancy and into the role of perinatal factors in determining infant growth and subsequent overweight/obesity risk. In part two of this thesis, the aims were to quantify vitamin D intake and status at 2 years and to investigate whether 25-hydroxyvitamin D [25(OH)D] concentrations in early pregnancy and in umbilical cord blood are associated with infant growth and body composition. There was a low prevalence of vitamin D deficiency among Irish 2 year olds (n = 742) despite a high prevalence of inadequate intakes and high latitude (51°N). Maternal 25(OH)D concentrations at 15 weeks gestation and cord 25(OH)D concentrations at delivery were not associated with infant growth or adiposity.