Disclosed are adjustable supports, bedding support assemblies, and foldable bed frames having adjustable supports, bedding support assemblies or both. A foldable bed frame includes first and second sub-frames, first and second leg assemblies, and a plurality of adjustable supports. First and second sub-frames are pivotally connected with each other at their proximal sides. First and second leg assemblies are pivotally connected with the first and second sub-frames, respectively. Each adjustable support has one end connected to a sub-frame, and the other end connected to a leg assembly. An adjustable support includes movably coupled inner and outer bars, and a locking and unlocking mechanism to selectively restrict the inner and outer tubular bars from moving with respect to each other and thus selectively restrict the leg assembly from rotating with respect to the sub-frame.