Both genders benefit from taking in a reasonable amount of sodium and possibly a small amount of carbohydrate with drinks during activity lasting multiple hours. This is especially true in hotter conditions, where sweat losses can be very high and the body needs to maintain high levels of blood plasma volume to allow the blood to transport heat to the skin and shuttle fuel and waste products to and from working muscles.
However, due to differences in average body size and composition, as well as hormonal fluctuations in the menstrual cycle, women’s need can be different to men’s at key times. Probably the most critical difference is that during the high hormone (luteal) phase of the cycle, women are significantly more likely to develop hyponatremia (low blood sodium levels, a condition that can be debilitating or fatal in extreme cases). This is because the hormones released in this phase reduce the amount of sodium retained by the kidneys, resulting in a decrease in overall blood volume and blunted thirst signals to the brain.
So women are strongly advised to drink to the dictates of thirst during this phase and to experiment with higher amounts of sodium in drinks to aid the preservation of blood volume.