The discrepancy between observational and intervention studies suggests that low 25(OH)D is a marker of ill health .
Inflammatory processes involved in disease occurrence and clinical course would reduce 25(OH)D , which would explain why low vitamin D status is reported in a wide range of disorders .
In elderly people , restoration of vitamin D deficits due to ageing and lifestyle changes induced by ill health could explain why low-dose supplementation leads to slight gains in survival
Low serum concentrations of 25-hydroxyvitamin D ( 25[OH]D ) have been associated with many non-skeletal disorders .
However , whether low 25(OH)D is the cause or result of ill health is not known .
Cross-sectional and prospective relationships of interleukin-6 and C-reactive protein with physical performance in elderly persons: MacArthur studies of successful aging.
BACKGROUND Chronic inflammation has been proposed as a biological mechanism underlying the decline in physical function that occurs with aging . The purpose of this investigation was to examine the cross-sectional and prospect i ve relationships between markers of inflammation , interleukin-6 ( IL-6 ) and C-reactive protein ( CRP ) , with several measures of physical performance in older persons aged 70 to 79 years . METHODS Subjects were 880 high-functioning men and women participating in the MacArthur Study of Successful Aging ( n = 1189 ) , a subset of the Established Population s for Epidemiologic Studies of the Elderly ( n = 4030 ) . Plasma  IL-6 and CRP levels were determined by enzyme-linked immunosorbent assay and log transformed to normalize the distributions . Physical function measures included h and grip strength , signature time , chair st and s ( time to complete five repetitions ) , and 6-m walk time . RESULTS Women had lower ( p < .05 ) IL-6 levels than men , but there was no significant difference between blacks and whites . IL-6 and CRP levels were higher ( p < .05 ) in current smokers than in nonsmokers and in those with a greater body mass index ( BMI ) . Hours per year undertaking moderate and strenuous physical activity were also related to inflammatory markers with higher ( p < .001 ) IL-6 and CRP levels in less active individuals . After adjusting for age , sex , race , BMI , smoking status , use of nonsteroidal anti-inflammatory drugs , and prevalence of morbidity , those in the top two quartiles for walking speed had lower ( p = .012 ) IL-6 levels than those in the bottom quartile . In addition , there was a trend ( p = .038 ) for lower CRP levels in those with higher walking speed . CRP levels were also lower ( p = .04 ) in individuals in the top quartile for grip strength . No significant differences were noted for chair st and s or signature time performance . Repeat performance measures obtained on 405 subjects ( 67 % of those eligible at baseline ) obtained 7 years later had declined significantly ( grip strength , 18 % ; signature time , 21 % ; walking speed , 31 % ; p < .001 ) , except for the chair rise ; however , baseline IL-6 and CRP were not associated with a change in performance . However , those who died or who were unable to undergo testing had higher baseline IL-6 and CRP levels ( p < .01 ) and slower walking speed ( p < .05 ) . CONCLUSIONS Although IL-6 has been shown to predict onset of disability  in older persons and both IL-6 and CRP are associated with mortality risk , these markers of inflammation have only limited associations with physical performance , except for walking measures and grip strength at baseline , and do not predict change in performance 7 years later in a high-functioning subset of older adults
The discrepancy between observational and intervention studies suggests that low 25(OH)D is a marker of ill health .
Inflammatory processes involved in disease occurrence and clinical course would reduce 25(OH)D , which would explain why low vitamin D status is reported in a wide range of disorders .
In elderly people , restoration of vitamin D deficits due to ageing and lifestyle changes induced by ill health could explain why low-dose supplementation leads to slight gains in survival
Low serum concentrations of 25-hydroxyvitamin D ( 25[OH]D ) have been associated with many non-skeletal disorders .
However , whether low 25(OH)D is the cause or result of ill health is not known .