Researchers here find that both reduced phosphate in the diet and use of a phosphate binding drug slow age-related loss of muscle mass in mice. It is an interesting result given the size of the effect. It has been proposed that high levels of phosphates observed in later life are relatively important in the constellation of many contributing mechanisms implicated in the onset of sarcopenia, the name given to this characteristic decline of muscle mass and strength. The data noted here seems a compelling demonstration of the point.
Sarcopenia is defined by the progressive and generalized loss of muscle mass and function associated with aging. We have previously proposed that aging-related hyperphosphataemia is linked with the appearance of sarcopenia signs. Because there are not effective treatments to prevent sarcopenia, except for resistance exercise, we propose here to analyse whether the dietary restriction of phosphate could be a useful strategy to improve muscle function and structure in an animal model of aging.
Five-month-old (young), 24-month-old (old) and 28-month-old (geriatric) male C57BL6 mice were used. Old and geriatric mice were divided into two groups, one fed with a standard diet (0.6% phosphate) and the other fed with a low-phosphate (low-P) diet (0.2% phosphate) for 3 or 7 months, respectively. A phosphate binder, Velphoro, was also supplemented in a group of old mice, mixed with a standard milled diet for 3 months.
Old mice fed with low-P diet showed reduced serum phosphate concentration (16.46 ± 0.77 mg/dL young; 21.24 ± 0.95 mg/dL old; 17.46 ± 0.82 mg/dL low-P diet). Old mice fed with low-P diet displayed 44% more mass in gastrocnemius muscles with respect to old mice. NMRI revealed a significant reduction in T2 relaxation time and increased magnetization transfer and mean diffusivity in low-P diet-treated mice compared with their age-matched controls. The low-phosphate diet increased the fibre size and reduced the fibrotic area by 52% in gastrocnemius muscle with respect to old mice. Twitch force and tetanic force were significantly increased in old mice fed with the low phosphate diet. Physical performance was also improved, increasing gait speed by 30% and reducing transition time in the static rod by 55%. Similar results were found when diet was supplemented with Velphoro.