Estrogen use by postmenopausal women is associated with significantly lower phosphorus levels, independent of age, race, dietary phosphorus intake, body mass index, renal function, and other factors, a new study suggests.

Among postmenopausal women, the mean serum phosphorus level was 3.83 mg/dL among those on estrogen therapy compared with 3.98 mg/dL among non-users of estrogen, investigators reported online ahead of print in the American Journal of Kidney Diseases.

“Our findings are intriguing if one considers the possibility that differences in serum phosphorus levels may contribute in part to the disproportionately higher cardiovascular morbidity and mortality in postmenopausal women,” the researchers observed.

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The researchers, led by Khashayar Sakhaee, MD, of the University of Texas Southwestern Medical Center in Dallas, explained that epidemiologic data have shown that increasing serum phosphorus levels within the normal range is associated with increased cardiovascular morbidity and mortality in the general population without chronic kidney disease.

Dr. Sakhaee and his colleagues analyzed data from 7,005 participants aged 21 years and older (3,785 women and 3,220 men) in the National Health and Nutrition Examination Survey (2003-2006).

In both men and women, serum phosphorus levels declined progressively with age. In men, the decline continues over the entire age range of 21-85 years, but the pattern is different in women. From age 21 to 45 years, the decline in serum phosphorus levels is similar in both men and women, but after age 46 years, “contemporaneous with the onset of menopause, serum phosphorus levels are consistently higher in women than men,” the researchers wrote.