Vitamin D status and cognitive performance in community-dwelling adults: A dose-response meta-analysis of observational studies.

Low vitamin D status is linked with poorer cognition in adults while findings in relation to high levels are mixed.We performed a systematic review and meta-analyses to examine dose-response associations between 25-hydroxyvitamin D (25OHD) levelsand cognitive performance in community-dwelling adults. Thirty-eight observational studies were included in dose-response meta-analyses. Positive, nonlinear associations were identified between baseline25OHD levels and global cognition incross-sectional and longitudinal analyses, and for performance in memory and executive function in longitudinal analyses. When restricted to studies involving older adults, thepattern emerged forspecific domains in cross-sectional analyses. Poorer performance was associated with low 25OHD levels, while a sharp improvement was associated withlevels up to 60-70 nM/L. Further improvement was observed only for longitudinal global cognition. Our findings support the association between low vitamin D and poorer cognition and suggest levels of at least 60 nM/L are associated with better cognition during ageing.

Investigating Potential Dose-Response Relationships between Vitamin D Status and Cognitive Performance: A Cross-Sectional Analysis in Middle- to Older-Aged Adults in the Busselton Healthy Ageing Study.

Low vitamin D status has been linked to adverse cognitive outcomes in older adults. However, relationships at higher levels remain uncertain. We aimed to clarify patterns of association between vitamin D status and cognitive performance, using flexible regression methods, in 4872 middle- to older-aged adults (2678 females) from the Busselton Healthy Ageing Study. Cross-sectional associations of serum levels of 25-hydroxyvitamin D (25OHD) and performance in cognitive domains were modelled using linear regression and restricted cubic splines, controlling for demographic, lifestyle, and health factors. Mean ± SD serum 25OHD levels were 78 ± 24 nM/L for women and 85 ± 25 nM/L for men. Increasing levels in women were associated with better global cognition (linear trend, p = 0.023) and attention accuracy (continuity of attention), with improvement in the latter plateauing around levels of 80 nM/L (nonlinear trend, p = 0.035). In men, increasing levels of serum 25OHD were associated with better attention accuracy (linear trend, p = 0.022), but poorer semantic verbal fluency (linear trend, p = 0.025) and global cognition (nonlinear trend, p = 0.015). We identified patterns of association between serum 25OHD levels and cognitive performance that may reflect early dose-response relationships, particularly in women. Longitudinal analyses extending through to older ages may help to clarify the nature, strength, and temporality of these relationships.

Charlson's Index was a poor predictor of quality of life outcomes in a study of patients following joint replacement surgery.

OBJECTIVE: We examined the predictive validity of Charlson's Index as a tool to measure and adjust for comorbidity in studies of health-related quality of life(HRQOL) outcomes after joint replacement surgery. STUDY DESIGN AND SETTING: SF-36 physical component summary scores were available for a cohort of patients who underwent primary hip or knee replacement surgery at one hospital over a 12-month period. Baseline comorbidity was assessed for the same group of patients using longitudinal hospital morbidity data from the Western Australia Department of Health. The presence or absence of individual conditions was determined, and Charlson's Index scores were calculated for each patient, using varying look-back periods. RESULTS: In regression analysis, Charlson's Index was a poor predictor of the HRQOL outcome scores, explaining a maximum 1.79% of the variance. In contrast, the presence or absence of a small number of individual conditions together explained between 5% and 7% of the variance. CONCLUSION: The findings suggest that Charlson's Index should not be used to adjust for HRQOL outcomes, particularly in this patient group with low levels of serious comorbidity. Alternative methods are needed for use in this context.