Superior bioavailability of the calcium salt form of -hydroxy--methylbutyrate compared with the free acid form

We investigated the bioavailability of the calcium salt (HMB-Ca) and the free acid (HMB-FA) forms of beta-hydroxy-beta-methylbutyrate (HMB). Sixteen young individuals received the following treatments on three different occasions in a counterbalanced crossover fashion: (1) HMB-FA in clear capsules; (2) HMB-Ca in gelatine capsules; (3) HMB-Ca dissolved in water. All treatments provided 1 g of HMB. Blood samples were taken before and on multiple time points following ingestion. The following parameters were calculated: peak plasma (Cmax), time to peak (Tmax), slope of HMB appearance in blood, area under the curve (AUC), half-life time (t (1/2) ) and relative bioavailability (HMB-Ca in water set as reference). All treatments led to rapid and large increases in plasma HMB. HMB-Ca in capsules and in water showed similar plasma HMB values across time (p = 0.438). HMB-FA resulted in lower concentrations vs. the other treatments (both p < 0.001). AUC (HMB-Ca in capsules: 50,078 +/- 10,507; HMB-Ca in water: 47,871 +/- 10,783; HMB-FA: 29,130 +/- 12,946 mu mol L-1 x 720 min), Cmax (HMB-Ca in capsules: 229.2 +/- 65.9; HMB-Ca in water: 249.7 +/- 49.7; HMB-FA: 139.1 +/- 67.2 mu mol L-1) and relative bioavailability (HMB-Ca in capsules: 104.8 +/- 14.9%; HMB-FA: 61.5 +/- 17.0%) were lower in HMB-FA vs. HMB-Ca (all p < 0.001). HMB-Ca in water resulted in the fastest Tmax (43 +/- 22 min) compared to HMB-Ca in capsules (79 +/- 40 min) and HMB-FA (78 +/- 21 min) (all p < 0.05), while t 1/2 was similar between treatments. To conclude, HMB-Ca exhibited superior bioavailability compared to HMB-FA, with HMB-Ca in water showing faster absorption. Elimination kinetics were similar across all forms, suggesting that the pharmaceutical form of HMB affects the absorption rates, but not its distribution or elimination.