Donating blood on a regular basis appears to reduce blood pressure, but appearances can be deceiving.

BACKGROUND: Previous studies have reported a relationship between blood donation and decreased risk for cardiovascular events, and it has been proposed that this may be due to a lowering of blood pressure among hypertensive individuals who donate on a regular basis. STUDY DESIGN AND METHODS: With the use of a retrospective longitudinal analysis, predonation blood pressure readings were examined across consecutive whole blood donations for New York Blood Center donors. With blood pressure levels recorded at the first, second, third, and fourth donations, the sample was divided into three subgroups including high (>= 140 mmHg), intermediate (> 100 and < 40 mmHg), and low (100 mmHg) systolic blood pressure (SBP). In addition, a computational approach was used to estimate regression to the mean effects for donors with high SBP or high diastolic blood pressure (DBP) at their first, second, or third donation. RESULTS: Visual examination of SBP and DBP patterns across donations revealed that, on average, donors with extreme values at one donation had relatively normal values at the other donations. Further, comparison of computed expected versus observed blood pressure decreases supported the notion of a subsequent regression to the mean among donors with elevated SBP or DBP at Donation 1, 2, or 3. CONCLUSION: Among individuals who are hypertensive at initial donation, reductions in blood pressure at subsequent donations appear to result from regression to the mean as opposed to a salutary physiologic process.