The reinforcement element for reinforcing the structure of a door of a vehicle extends along a main direction and comprises at least a main portion having a reinforcing cross-section (40) extending in a plane substantially perpendicular to the main direction. The reinforcing cross-section (40) includes at least four adjacent branches (42a, 42b, 42c, 42d, 42e, 42f, 42g), each extending in different directions, two successive branches forming a non-zero angle, at least two of the non-zero angles being of opposite signs.