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 .
Elevated C-reactive protein levels, psychological distress, and depression in 73, 131 individuals.
CONTEXT The pathogenesis of depression is not fully understood , but studies suggest that low- grade systemic inflammation contributes to the development of depression . OBJECTIVE To test whether elevated plasma levels of C-reactive protein ( CRP ) are associated with psychological distress and depression . DESIGN We performed cross-sectional and prospect i ve analyses of CRP levels in 4 clinical ly relevant categories using data from 2 general population studies . SETTING The Copenhagen General Population and the Copenhagen City Heart studies . PARTICIPANTS We examined 73 131 men and women aged 20 to 100 years . MAIN OUTCOME MEASURES We ascertained psychological distress with  2 single-item self-reports and depression using self-reported antidepressant use , register-based prescription of antidepressants , and register-based hospitalization with depression . RESULTS In cross-sectional analyses , increasing CRP levels were associated with increasing risk for psychological distress and depression ( P = 3 × 10 - 8 to P = 4 × 10 - 105 for trend ) . For self-reported use of antidepressants , the odds ratio was 1.38 ( 95 % CI , 1.23 - 1.55 ) for CRP levels of 1.01 to 3.00 mg/L , 2.02 ( 1.77 - 2.30 ) for 3.01 to 10.00 mg/L , and 2.70 ( 2.25 - 3.25 ) for greater than 10.00 mg/L compared with 0.01 to 1.00 mg/L. For prescription of antidepressants , the corresponding odds ratios were 1.08 ( 95 % CI , 0.99 - 1.17 ) , 1.47 ( 1.33 - 1.62 ) , and 1.77 ( 1.52 - 2.05 ) , respectively ; for hospitalization with depression , 1.30 ( 1.01 - 1.67 ) , 1.84 ( 1.39 - 2.43 ) , and 2.27 ( 1.54 - 3.32 ) , respectively . In prospect i ve analyses , increasing CRP levels were also associated with increasing risk for hospitalization with depression ( P = 4 × 10 - 8 for trend ) . CONCLUSIONS Elevated levels of CRP are associated with increased risk for psychological distress and depression in the general population
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 .