Effects of gender and body weight on fibroblast growth factor 23 responsiveness to estimated dietary phosphorus.

Fibroblast growth factor 23 (FGF23) is a molecule involved in regulating phosphorus homeostasis. Although some studies indicated an association between serum FGF23 levels and sex, the association has not been fully investigated. The purpose of this study was to evaluate whether sex could influence FGF23 responsiveness to dietary phosphorus intake in healthy individuals. Thirty two healthy subjects between 21 and 28 years were recruited for this study. Subjects performed 24-hour urine collection and blood samples were collected. We estimated phosphorus intake (UC-P) from the urine collection (UC), and evaluated any association between UC-P and serum FGF23 levels. Subsequently, we compared serum FGF23 levels between males and females. Positive correlation was observed between UC-P and serum FGF23 levels. Serum FGF23 levels were significantly higher in males than in females. Serum FGF23 levels/UC-P was significantly higher in females than in males. There was no significant difference in serum FGF23 levels/UC-P/BW between the male and female groups. Our results indicate that there was no gender difference between FGF23 responsiveness to phosphorus intake per body weight.

Nocturnal eating disturbs phosphorus excretion in young subjects: a randomized crossover trial.

BACKGROUND: Nocturnal eating have recently increased. Serum phosphorus levels and regulators of phosphorus have circadian variations, so it is suggested that the timing of eating may be important in controlling serum phosphorus levels. However, there have been no reports on the effects of nocturnal eating on phosphorus metabolism. The objective was to evaluate the effects of nocturnal eating on phosphorus metabolism. METHODS: Fourteen healthy men participated in two experimental protocols with differing dinner times. The design of this study was a crossover study. The subjects were served test meals three times (breakfast; 07:30 h, lunch; 12:30 h, dinner; 17:30 or 22:30 h) a day. Blood and urine samples were collected to assess diurnal variation until the following morning. RESULTS: The following morning, fasting serum phosphorus levels in the late dinner group were markedly higher than those in the early dinner group (p < 0.001), although serum calcium levels were maintained at approximately constant levels throughout the day in both groups. Fluctuations in urinary calcium excretion were synchronized with the timing of dinner eating, however, fluctuations in urinary phosphorus excretion were not synchronized. Urinary phosphorus excretions at night were inhibited in the late dinner group. In the late dinner group, intact parathyroid hormone levels didn't decrease, and they were significantly higher in this group compared with the early dinner group at 20:00 h (p = 0.004). The following morning, fasting serum fibroblast growth factor 23 levels in the late dinner group had not changed, but those in the early dinner group were significantly increased (p = 0.003). Serum free fatty acid levels before dinner were significantly higher in the late dinner group compared with the early dinner group. CONCLUSIONS: Our results indicate that nocturnal eating inhibits phosphorus excretion. It is suggested that nocturnal eating should be abstained from to manage serum phosphorus levels to within an adequate range.