The hypotensive effects of conventional non-fat dairy products : the role of arterial stiffness
High consumption of dairy products, particularly non-fat dairy, is associated with reduced risk of high blood pressure and vascular dysfunction. Currently, it is not known if the solitary addition of conventional non-fat dairy products to the normal routine diet is capable of reducing blood pressure or improving vascular function. Accordingly, the primary aims of the present study were to determine if the solitary addition of conventional non-fat dairy products to the normal routine diet would reduce blood pressure and improve vascular function in middle-aged and older adults with elevated blood pressure. Using a randomized, crossover intervention study design, forty-nine adults with elevated blood pressure underwent a High Dairy condition (+4 servings/day of conventional non-fat dairy products) and isocaloric No Dairy condition (+4 servings/day fruit products) in which all dairy products were removed. Both dietary conditions lasted 4 weeks with a 2-week washout before crossing over into the alternate condition. In Study 1, the High Dairy condition produced reductions in brachial systolic blood pressure and pulse pressure. The hypotensive effects were observed within three weeks after the initiation of dietary intervention and in both casual seated and ambulatory (24-hour) measurements. On the contrary, pulse pressure was increased after removal of all dairy products in the No Dairy condition compared to baseline and after in the High Dairy condition. There were no changes in diastolic blood pressure after either dietary condition. In Study 2, the High Dairy condition produced reductions in carotid systolic blood pressure, pulse pressure, and carotid-femoral pulse wave velocity with a concomitant increase in brachial flow-mediated dilation and cardiovagal baroreflex sensitivity. Brachial flow-mediated dilation decreased and carotid pulse pressure increased after removal of all dairy products in the No Dairy condition. Furthermore, [delta] carotid systolic blood pressure and carotid-femoral pulse wave velocity were highly related. Taken together, we concluded that the solitary manipulation of conventional dairy products, particularly non-fat dairy, in the normal routine diet would modulate levels of blood pressure and vascular function in middle-aged and older adults with pre-hypertension and hypertension.