Vitamin D status and biomarkers of functional health and ageing in very-old adults : analysis of the Newcastle 85+ study

Abstract

The number of those aged over 80 years-old (the “very-old”) will increase from 5% of the population in European countries in 2010, to more than 10% of the population by 2050 (OECD, 2013). Very little is known about the nutritional intake, nutritional status and its association with health and wellbeing in the very-old. Due to its diverse biological effects, vitamin D has gained immense interest recently as a potential modifier for a range of health outcomes This PhD systematically reviewed the available literature to provide an accurate snapshot of vitamin D status in the very-old. It also used a unique dataset from the Newcastle 85+ Study, a longitudinal community-dwelling study of health trajectory and outcomes conducted in over 800 people from the North-East of England aged 85 years. The overall aim of using this data were to explore vitamin D association with a range of functional and ageing biomarkers in the very-old. Vitamin D status [25(OH)D] was available for 775 participants, and measured by immunoassays at baseline only and divided to the following concentration: <25 nmol/l (low), 25-50 nmol/l (moderate), and >50 nmol/l (high). Disability was measured using a questionnaire on the difficulty of performing 17 Activities of Daily Living at baseline, 1.5, 3 and 5 years. NTproBNP was measured using an electrochemiluminescent sandwich immunoassay. The HbA1c was measured using a Tosoh Eurogenetics automated HLC-723G7 HPLC analyser. Telomere Length was measured as an abundance of telomeric template vs. a single gene by quantitative real-time PCR. Spirometry and peak flow measurements were to obtain three technically satisfactory maximal effort ‘blows’ to generate reproducible FEV1and FVC. Results of the systematic review showed that prevalence of deficiency varies by latitude and living conditions of the participants, and that vitamin D deficiency is widespread in many regions, particularly in Europe. Using the Newcastle 85+ Study data also showed a high prevalence of vitamin D deficiency (>30%) was found amongst very-old adults. Findings of this thesis indicate that participants with low 25(OH)D concentration (<25 nmol/l) were more likely to have a poorer disability trajectory over 5 years compared with those with moderate concentration (25–50 nmol/l) (OR= 3.12, 95% CI= 1.6–5.8, p= 0.001), although physical activity was the strongest predictor of disability trajectories. However, this thesis could not prove the protective effect of vitamin D in regards to metabolic and cardiopulmonary health biomarkers (NT-proBNP, HbA1c, FEV1, FVC and diastolic blood pressure) in fully adjusted models at baseline or over 18 and 36 months. Finally, high 25(OH)D concentration is positively associated with Telomere Length (95%CI= 12.0-110.3, B= 61.2+25.0, p=0.015) but does not have protective effects over 18 and 36 months. In conclusion, this thesis highlights that vitamin D deficiency is very common in very-old adults and that low vitamin D status is associated with at least some functional and ageing biomarkers in this under studied age group.