Effect of adiposity on vitamin D status and the 25-hydroxycholecalciferol response to supplementation in healthy young and older Irish adults.

There is increasing epidemiological evidence linking sub-optimal vitamin D status with overweight and obesity. Although increasing BMI and adiposity have also been negatively associated with the change in vitamin D status following supplementation, results have been equivocal. The aim of this randomised, placebo-controlled study was to investigate the associations between anthropometric measures of adiposity and the wintertime serum 25-hydroxycholecalciferol (25(OH)D) response to 15 µg cholecalciferol per d in healthy young and older Irish adults. A total of 110 young adults (20-40 years) and 102 older adults ( ≥ 64 years) completed the 22-week intervention with >85 % compliance. The change in 25(OH)D from baseline was calculated. Anthropometric measures of adiposity taken at baseline included height, weight and waist circumference (WC), along with skinfold thickness measurements to estimate fat mass (FM). FM was subsequently expressed as FM (kg), FM (%), FM index (FMI (FM kg/height m2)) and as a percentage ratio to fat-free mass (FFM). In older adults, vitamin D status was inversely associated with BMI (kg/m2), WC (cm), FM (kg and %), FMI (kg/m2) and FM:FFM (%) at baseline (r - 0·33, - 0·36, - 0·33, - 0·30, - 0·33 and - 0·27, respectively, all P values < 0·01). BMI in older adults was also negatively associated with the change in 25(OH)D following supplementation (ß - 1·27, CI - 2·37, - 0·16, P = 0·026); however, no such associations were apparent in younger adults. Results suggest that adiposity may need to be taken into account when determining an adequate wintertime dietary vitamin D intake for healthy older adults residing at higher latitudes.

Maintenance of wintertime vitamin D status with cholecalciferol supplementation is not associated with alterations in serum cytokine concentrations among apparently healthy younger or older adults.

Epidemiological studies have shown that low vitamin D status results in impaired immune function and is associated with the prevalence of autoimmune and inflammatory conditions. Vitamin D supplementation has been shown to reduce circulating concentrations of inflammatory markers in such conditions. However, the possible beneficial effect of vitamin D supplementation in the general population, particularly for those individuals living at high latitudes where hypovitaminosis D is common during wintertime, remains unclear. The aim of this study was to assess the effect of vitamin D supplementation using doses of 5, 10, and 15 µg/d cholecalciferol (D3) compared with placebo on cytokine concentrations throughout winter in apparently healthy younger (aged 20-40 y) and older (aged ≥64 y) adults. A total of 211 younger and 202 older adults completed the 22-wk intervention (from October to March) with >85% compliance. Serum concentrations of 25-hydroxycholecalciferol [25(OH)D3], high sensitivity C-reactive protein, IL-6, IL-10, soluble CD40 ligand, TGFß, TNFα, and fibrinogen were measured using ELISA. 25(OH)D3 concentrations significantly decreased in the placebo and 5 and 10/d µg D3 groups in the younger cohort and in the placebo group in the older cohort. Whereas 15 µg/d D3 supplementation maintained 25(OH)D3 concentrations in the younger cohort (baseline, 75.9 nmol/L; postintervention, 69.0 nmol/L) and significantly increased concentrations in the older cohort (baseline, 55.1 nmol/L; postintervention, 73.9 nmol/L), it had no significant effect on cytokine concentrations (ANCOVA, P > 0.05). The long-term effects of low vitamin D status remain to be elucidated and optimization of vitamin D status in otherwise healthy individuals may potentially have lasting beneficial effects on the immune system.

Obesity and inflammation: the effects of weight loss.

Following the discovery of TNF-alpha and leptin as secretory products of adipocytes in the early 1990s, subsequent obesity research focused on the new functional role of adipose tissue, as an active endocrine organ. Many more inflammatory peptides have been linked to adiposity, which ultimately characterised obesity as a state of low-grade systemic inflammation, or 'metaflammation' which may link obesity to its co-morbidities. The aim of the present review is to examine the effects of weight loss on inflammation in overweight and obese, but otherwise healthy, populations. Studies were broadly classified into four types (diet, physical activity, diet and physical activity combined, and surgical interventions) and discussed according to the method used to induce weight loss. All studies measured at least one obesity-related inflammatory marker (ORIM). The overall finding from the present review is that weight loss does improve inflammation in terms of both the inflammatory (C-reactive protein, TNF-alpha, IL-6 and leptin) and anti-inflammatory (adiponectin) ORIM. Within this, the greatest improvements in ORIM are observed in studies achieving a weight loss of at least 10 %. However, a number of methodological issues have been identified as potential limitations within the literature including the sex and age of subjects, sample size, study duration and the assessment of body composition. In conclusion, although a period of weight loss per se is capable of reversing the unfavourable inflammatory profile evident in the obese state, further studies are required to determine the time needed, in which a reduced weight is maintained, in order to benefit from improved inflammatory status long term.