RT Journal
A1 Hemilä H
T1 VItamin d level, respiratory tract infections, and controlled trials
JF Archives of Internal Medicine
JO Archives of Internal Medicine
YR 2009
FD August 10
VO 169
IS 15
SP 1443
OP 1443
DO 10.1001/archinternmed.2009.246
UL http://dx.doi.org/10.1001/archinternmed.2009.246
AB 
Nutrition is associated with a wide range of lifestyle variables, and there is a great risk of residual confounding caused by inadequate adjustments for complex social and environmental exposures acting over a person’s life.2 Residual confounding may explain, for example, the divergent findings in observational studies and controlled trials on vitamin E.2 Therefore, great caution should be exercised when interpreting correlations between serum vitamin D levels and health outcomes.