EPIDEMIOLOGIC EVIDENCE OF AN INTERACTION BETWEEN CALCIUM AND SODIUM-INTAKE IMPACTING ON BLOOD-PRESSURE - A MONTREAL STUDY

Nutritional calcium and sodium are considered to be important regulators of blood pressure. This study was performed on 182 randomly selected Canadians from Montreal to test the relative contribution of these ions to systolic and diastolic blood pressure, as well as their interaction with other demographic indices. Multiple analysis of the total study population revealed that 28% (P < .001) of systolic blood pressure was predicted by gender, sodium, and calcium interaction (P = .003), weight, and the additive effect of age and weight. The same characteristics contributed to 37% (P < .001) of diastolic blood pressure with an additional contribution of alcohol intake. Analysis by terciles of sodium and calcium intake indicated that the positive effect of sodium on blood pressure occurred only in subjects given a low calcium diet, whereas blood pressure was lowest in the tercile of both high calcium and sodium intake. The impact of the sodium and calcium interaction on blood pressure represented as much as a 10 mm Hg decrement of systolic blood pressure with 400 mg calcium/1000 kcal intake at the highest level of sodium consumption and a 6 mm Hg decrease for diastolic blood pressure. In subjects without a family history of hypertension, the same indices contributed up to 53% of systolic and 55% of diastolic blood pressure with a synergetic effect of sodium and calcium, indicating that blood pressure was lowest in subjects given a high calcium and sodium diet. For subjects with a family history of hypertension, there was no significant impact of sodium, whereas calcium intake contributed negatively to both systolic and diastolic blood pressure. This study suggested a significant protective effect of nutritional calcium, most evident on a high sodium intake, particularly in the absence of a family history of hypertension.