Vitamin D in the Irish Population: an analysis of prevalence and determinants

Abstract

Introduction: Vitamin D has an established role in bone and muscle health, with deficiency causing rickets in children, osteomalacia in adults and contributing to the development of osteoporosis. More recently it has been associated with extra-skeletal effects including inflammation, cardiovascular disease (CVD), diabetes, cognitive impairment, and respiratory conditions including asthma and COVID. Due to a northern latitude (51-55°N), and limited dietary intake, the Irish population are at risk of vitamin D deficiency. However, much is unknown about the status in the population with regard to particular groups including children, ethnic minorities, urban dwellers, and younger adults. There is also a lack of research on vitamin D testing in Ireland including indications for same and the associated costs. Furthermore, no recent studies have assessed vitamin D intake in Irish adults, and few have examined peoples understanding of vitamin Ds role in health. This PhD aims to review existing research to-date in Ireland on vitamin D, and to investigate vitamin D status and its associated determinants in an Irish population. Furthermore, it explores vitamin D retesting, with a focus on inappropriate testing and its associated costs.

Methods: A literature review of existing evidence examining vitamin D status and intake between 1990-2022 in Ireland (Republic and Northern Ireland) was undertaken. To examine vitamin D status in the Irish population, a database of patients who had 25(OH)D serum concentration assessed by Liquid Chromatography Tandem Mass Spectrometry at St James’s Hospital Dublin between 2014-2020 at the request of Primary Care physicians was generated. Statistical analysis was used to determine vitamin D status and its predictors in children (1-17 years) and adults (>18 years), including non-nationals. Vitamin D retesting and associated costs were also ascertained. Finally, a stratified sample of participants completed a questionnaire to further explore the biophysical, lifestyle and dietary determinants of vitamin D status.

Results: From the comprehensive literature review, 142 studies and 7 reports were identified. Vitamin D deficiency (<30 nmol/L) was prevalent in Ireland, in up to 32% of older adults (>50 years), 38% of adults (<50 years) and 68% of children (<18 years). Adolescents, younger adults, and ethnic minorities were at greatest risk. Dietary intake was lowest in children and pregnant women, and highest in older adults. Results of our first investigation based on data analysis of community dwelling adults (n=36,466) found 15% were vitamin D deficient (<30 nmol/L), increasing to 23% in winter. Younger adults (18-39 years), males and those living in low socioeconomic locations were most at risk. In my second study, one in four adults were found to have vitamin D levels retested, with inappropriate testing resulting in €60,000 of estimated wasted expenditure per annum to St James’s hospital. In the third study, based on an analysis of vitamin D results of 1,226 children, 23% were vitamin D deficient, with a higher prevalence in females, older children (>12 years) and those living in poorer socioeconomic areas. Finally in my fourth study, total dietary vitamin D intake, ethnicity and sun habits were found to be important predictors of vitamin D status. Awareness of vitamin D supplementation recommendations and testing indications were poor, though knowledge of its importance for bone health were well known.

Conclusion: Vitamin D deficiency is highly prevalent, with a lack of research in subgroups of the population at risk of deficiency including children, younger adults, pregnant women, and ethnic groups. We also identified that younger adults, adolescents, and those living in low socioeconomic areas were most at risk of deficiency. Despite vitamin D retesting being common, there was no research on its testing indications, with many adults having levels assessed for non-specific reasons and at considerable cost. The majority of adults were also not meeting a dietary vitamin D intake of 10 μg/day and had poor awareness of the current recommended dietary allowance. The findings suggest that public health measures to address deficiency in the Irish population are urgently required, such as systematic fortification of staple foods, and establishing targeted recommendation for vulnerable population groups. In addition, clear guidance for General Practitioners and the public on the appropriate indications for vitamin D testing is necessary to reduce inappropriate referrals and expenditure.