We present an Adaptive Beaconing Medium Access Control (AB-MAC) protocol based on time division multiple access (TDMA) in order to provide healthcare services. The purpose of our protocol is to gain not only energy-efficiency but also provide low delivery latency when both periodic data and event-driven data are present. In order to satisfy these requirements, we propose standby slots that are deployed during each beacon interval. The standby slots are able to identify unscheduled data with low delivery latency. An adaptive beacon is then provided that quickly reschedules the time slots. Furthermore, the AB-MAC asymmetrically assigns energy consumption to a hub instead of the sensor nodes when possible in order to reduce node's energy waste. In this paper, we evaluate IEEE 802.15.4 and AB-MAC in energy consumption and delivery latency. The simulation results indicate that the AB-MAC outperforms than IEEE 802.15.4 in BSNs.