Relation between Sodium Balance and Menstrual Cycle Symptoms in Normal Women

Abstract

OBJECTIVE: To determine whether sodium balance affects expression of menstrual symptoms. DESIGN: Prospective study of menstrual symptoms during three cycles: a baseline month (usual intake of sodium, 115 mmol/d) followed by 2 months of sodium restriction (intake of sodium, 73.0 mmol/d). Added salt was allowed during the last month. Investigators were aware of the diet sequence. SETTING: Outpatient. Meals were prepared by a metabolic kitchen during the 2 months that the participants received salt-restricted diets. PARTICIPANTS: 13 healthy menstruant women. MEASUREMENTS: Plasma sodium levels, urinary sodium excretion, and plasma renin activity were measured for five time periods during the baseline cycle and the two cycles of salt-restricted diet. Eleven women completed a questionnaire assessing somatic symptoms and sensory cravings at the same time every day during the 3-month study period. RESULTS: Sodium restriction was associated with a mean decrease (+/- one half of the 95% CI) in plasma sodium levels of 0.9 +/- 0.9 mmol/L from a mean of 139.3 mmol/L during the baseline cycle (P = 0.018), a decrease in urinary sodium excretion of 40.3 +/- 18 mmol/d from a mean of 117 mmol/d during the baseline cycle (P = 0.001), and an increase in plasma renin activity of 0.14 +/- 0.08 ng/(L . s) from a mean of 0.28 ng/(L . s) during the baseline cycle (P = 0.008). During the luteal phase of the sodium restriction cycle, significant decreases in plasma sodium levels of 1.23 +/- 0.5 mmol/L (from values of 138.8 mmol/L during the follicular phase) and increases in urinary sodium excretion of 27.2 +/- 10 mmol/d (from values of 65.5 mmol/d during the follicular phase) preceded periods when menstrual symptoms were most severe. Ratings of breast tenderness increased sixfold to eightfold in the late luteal phase (P < 0.001) and those of swelling or bloating increased twofold to threefold during early menses (P < 0.001) compared with nadir symptom ratings during each cycle. Sodium cravings increased in the luteal phase of all cycles but were not accompanied by increased sodium intake when access to added salt was allowed. CONCLUSIONS: Breast tenderness and bloating did not result from sodium retention in the luteal phase of the menstrual cycle. During normal and sodium-restricted diet cycles, women actually had urinary sodium loss, not retention, during the luteal phase; severity of menstrual symptoms was unchanged.