Yes. But the effect is relatively small, as compared to things like infrastructure or motorist behavior. Which leads to results like :>>1332296
What's also demonstrated is that mandatory helmet laws don't work for anyone but children. Other effects are much larger than the effectiveness of helmets.
Driving conditions are so different from place to place that a study in one location might not apply properly to others.
There are a number of conditions where the effect is much stronger. For children, and new riders. Night. Offroad. Near max effort. High speeds, or next to high speed traffic without a physical separator. Possibly being a woman.