FGF23 has been associated with frailty and functional performance in older individuals, but the association to sarcopenia is unknown.

To investigate the association between FGF23, frailty, sarcopenia and fractures in older community dwelling women.

Prospective longitudinal cohort study.

Malmö, Sweden.

995 75-year-old women, followed prospectively for ten years, with re-investigations after five (n=667) and ten (n=324) years.

C-terminal levels of FGF23 were measured and a frailty index of ‘deficits in health’ created. Sarcopenia was defined by low muscle mass and strength and “probable sarcopenia” by low muscle mass only. Incident fractures were continuously registered for 10-years. Based on tertiles of FGF23, odds ratio for frailty, sarcopenia and probable sarcopenia was investigated using logistic regression models adjusted for: eGFR, PTH, calcium, vitamin D and phosphate. Fracture-free survival during 10-year follow-up was depicted using Kaplan Meier curves.

While fracture-free survival did not differ between tertiles, women in the highest tertile of FGF23 had lower muscle strength and gait speed, and higher proportion with impaired mobility at baseline. At age 75, these women had higher odds of also being frail (ORadj 1.6 (95% CI 1.1–2.4)) and suffering from probable sarcopenia (ORadj 1.8 (95% CI 1.1–3.1)), but not sarcopenia. At follow-up the association between FGF23 and probable sarcopenia was not evident. While the association with frailty was attenuated at age 80 after adjustment (ORadj 1.6 (95% CI 1.0–2.5)), women in the highest tertile had higher odds of being frail at age 85 (ORadj 3.4 (95% CI 1.7–6.6)).

FGF23 may be a promising clinical marker for muscle strength, functional performance, and frailty in older women, but not for future fragility fractures. Whether FGF23 is also associated with sarcopenia requires further investigation.