Evidence exists that women have lower orthostatic tolerance than men
during quiescent standing. Water ingestion has been demonstrated to
improve orthostatic tolerance in patients with severe autonomic
dysfunction. We therefore sought to test the hypothesis that water
ingestion would improve orthostatic tolerance in healthy young women
more than in aged-matched men. Thirty seven (22 men and 15 women)
healthy subjects aged 22.5± 1.7 and 21.5±1.4 (means±SD)
respectively, ingested 50ml (control) and 500ml of water 40min before
orthostatic challenge on two separate days of appointment in a
randomized controlled, cross-over design. Seated and standing blood
pressure and heart rate were determined. Orthostatic tolerance was
assessed as the time to presyncope during standing. Ingesting 500ml of
water significantly improves orthostatic tolerance by 22% (32.0 ±
5.2 vs 26.2 ± 2.4min; p< 0.05) in men and by 33% (24.2±2.8
vs 18.3 ± 3.2; p< 0.05) in women. Thirty minutes after
ingesting 500ml of water, seated systolic blood pressure, diastolic
blood pressure, pulse pressure and mean arterial pressure rose
significantly in men while only systolic blood pressure and pulse
pressure rose significantly in women. However ingesting 500ml of water
did not have significant effect on seated heart rate in both men and
women. Ingestion of 500ml of water significantly attenuated both the
orthostatic challenge-induced increased heart rate and decreased pulse
pressure responses especially in women. Diastolic blood pressure tended
to be positively correlated with orthostatic tolerance strongly in men
than in women. Pulse pressure correlated positively while heart rate
correlated negatively to orthostatic tolerance in women but not in men
independent of other correlates. Water ingestion is associated with
orthostatic tolerance strongly in women but weakly in men independent
of other correlates. In conclusion, the findings in the present study
demonstrated that water ingestion caused improvement strongly in young
women than in young men. This improvement is associated with increased
pulse pressure and decreased tachycardiac responses during orthostatic
challenge