Water retention—a cause of bloating—is associated with changes in sex hormone levels. Many women experience water retention during menopause, but how sex hormones affect water balance is not understood. A new study in in the American Journal of Physiology—Renal Physiology sheds light on the connection, finding that sex hormones can directly control how the body reabsorbs water.
Water level in the body is maintained by the kidneys, which controls the amount of water reabsorbed from the blood they filter. Water is reabsorbed through channels called aquaporin 2 (AQP2) that are found along the kidneys' ducts. How much is reabsorbed is affected by the amount of AQP2.
Female rats with their ovaries removed produced less urine and had more AQP2 channels in their kidneys compared with female rats with ovaries. Treating the rats with the female sex hormone estradiol increased urine output and decreased the amount of AQP2. According to the researchers, the data supported that estradiol had an inhibitory effect on AQP2, meaning the lower the estradiol level, the greater the water retention. Changes in sex hormone levels over the menstrual cycle may affect the kidneys' water handling, and the reduced level of hormones during menopause may explain the greater water retention, the researchers wrote.