Serum alkaline phosphatase (ALP) could be an indicator of osteoblastic activity, which initiates hematopoietic stem cell (CD34-positive cell) production in bone marrow. Since chronic inflammation, which is a known risk factor for hypertension and endothelium dysfunction, stimulates bone marrow activity, ALP could be positively associated with hypertension. To clarify those associations, we conducted a cross-sectional study of 479 elderly Japanese men aged 60-69. Circulating CD34-positive cell levels could influence associations between serum ALP and hypertension because CD34-positive cell production is also a factor known to contribute to endothelial repair. Therefore, participants were stratified by the median value of circulating CD34-positive cell levels (1.00 cells/μL). A low level of circulating CD34-positive cells was identified in 240 members of the study population. A significantly positive association of ALP with hypertension was detected among participants with low circulating CD34-positive cell levels (multivariable-OR (odds ratio) for hypertension resulting from a 1 standard deviation (SD) increment in serum ALP (58.3 IU/L) = 1.44 (1.06, 1.95)) but not among those with high CD34-positive cell levels (multivariable-OR=0.91 (0.67, 1.23)). We also observed a significant effect of the interaction of circulating CD34-positive cell levels on the association between serum ALP and hypertension (multivariable p=0.011). Serum ALP was found to be positively associated with hypertension among elderly participants with low but not with high circulating CD34-positive cell levels. Since CD34-positive cells are a factor known to contribute to endothelial repair, capability for endothelial repair can be expected to have an effect on the association between serum ALP and hypertension
