Salt intake and bone health in menopausal women

A low-salt diet does not necessarily translate to stronger bones in postmenopausal women, physician-scientists report.

New findings suggest that a low-salt diet does not necessarily help improve bone health in menopausal women. Corresponding author Dr. Laura D. Carbone said, “When we started the study, we thought we were going to be telling everyone again that a low-salt diet is good for your bones. Instead, our message is, low-sodium intake by itself is not likely to be beneficial to your bones. We definitely don’t want to go further than that and say high sodium is good for them.”

The association of high sodium intake and weaker bones seems logical. Sodium and calcium are both stored in the bone. Sodium increases calcium excretion and low calcium is associated with low bone mineral density, an indicator of fracture risk. While calcium can't really be added to bone after the teen years, it can continue to follow sodium out of the bone and into the urine lifelong.

Guidelines from the Osteoporosis Foundations recommend a low-sodium diet, but the new study examines if there is any benefits to bone from it.

MCG physician-scientists looked at data on nearly 70,000 postmenopausal women followed for 11 years as part of the Women's Health Initiative, or WHI. WHI is a long-term National Institutes of Health-funded study of more than 160,000 postmenopausal women focused on ways to prevent heart disease, breast and colorectal cancer, and osteoporosis. They had fracture data on all the women included in their assessment and bone mineral density studies, an indicator of bone strength, on about 4,400.

Their findings were mixed, revealing that salt intake was not a contributing factor to poor bone health. Some studies found that higher salt intake was associated with stronger bones. When they factored in body mass index (BMI), no association was found between salt intake, bone density, and fracture rates.

Possible explanation for the findings stems from the fact that when sodium intake drops, the body has a natural mechanism to increase bone resorption.

A prospective study will enable more detailed examination of sodium intake, including periodic measures of sodium levels in the urine on some holidays and weekends, times when sodium intake tends to increase for most people, Carbone notes. The WHI nutrition data comes largely from the women's self-reports, with a correction factor applied based on the few who did have their urine tested for sodium levels.

The MCG team says that a diet high in calcium—including foods such as milk, yogurt, cheese and some green, leafy vegetables—and staying active are definitely good for the bones at any age.

The National Osteoporosis Foundation recommends limiting the intake of processed and canned foods, which are typically high in salt, as well as the salt you add to food. It recommends limiting salt intake to about 2,400 milligrams daily, which is about the same level as federal nutrition guidelines.

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