Collaborative overview ('meta-analysis') of prospective observational studies of the associations of usual blood pressure and usual cholesterol levels with common causes of death: protocol for the second cycle of the Prospective Studios Collaboration

Background Many prospective studies have been reported on the associations of blood pressure and blood cholesterol with cardiovascular disease, but fe w have been large enough to provide reliable estimates of the nature of the se associations in different circumstances or to characterize the associati ons with non-vascular causes of death. Moreover, almost all such reports ha ve related risk to baseline measurements of the risk factor of interest, wh ich can lead to substantial underestimation of the importance of the risk f actor due to 'regression dilution' bias. Objective By appropriate combination of data on individual participants fro m all such studies in a systematic 'meta-analysis: with correction for regr ession dilution, to characterize more precisely than has previously been po ssible the age-specific and sex-specific relevance of blood pressure and bl ood cholesterol levels to particular causes of death. Methods Information has been made available on about 175 000 deaths (45% du e to vascular disease and 20% due to cancer) among more than 1.4 million in dividuals followed for an average of 14 years in over 60 prospective studie s of blood pressure and blood cholesterol (with data on high-density lipopr otein cholesterol available for a substantial subset of individuals). This represents approximately 95% of the data from all relevant studies. (C) 199 9 Lippincott Williams & Wilkins.