Sex differences in casual and ambulatory blood pressure responses to extreme changes in dietary sodium.

OBJECTIVE: To compare the awake ambulatory and seated casual blood pressure responses to extreme changes in dietary sodium during a 4-month period between borderline hypertensive men (n = 24, aged 51+/- 7 years) and women (n = 8, aged 47+/- 8 years).
METHODS: Seated casual and awake ambulatory (over an average of 9 h, n = 32 readings) blood pressures were recorded at the end of 1-month trials of low (24 +/- mmol/day for men, 32 +/- 19 mmol/day for women) and high (330 +/- 101 mmol/day for men, 298 +/- 76 for women) intakes of dietary sodium. There was a 1-month interim period between the two trial periods and energy and potassium intake were maintained constant over the entire course of the study.
RESULTS: Among men, there was a similar average increase in blood pressure on going from the low- to the high-sodium diets according to the two methods of measurement, but among women there was a significant difference between the methods, such that the change in ambulatory blood pressure was less than the change in casual blood pressure. Women's casual blood pressure increased by 14/7 mmHg more than did their ambulatory blood pressure, whereas men's ambulatory blood pressure increased by 5/2 mmHg more than did their casual blood pressure (sex difference P < 0.009 for systolic and P < 0.037 for diastolic blood pressures). Finally, there was at best only modest concordance between changes in casual and ambulatory blood pressures between diets in individual patients, regardless of their sex, although men were more likely to have similar changes in their casual and ambulatory measurements than were women.
CONCLUSION: The determination of the sensitivity of blood pressure to dietary sodium intake may depend upon how blood pressure is measured. There may also be an interaction between sex and blood pressure measurement technique that could affect the determination of salt-sensitivity differences between men and women.