Final answer:
Calcium is the key nutrient that reduces the risk of cardiovascular disease for adults over 51.
Step-by-step explanation:
The key nutrient known to reduce the risk of cardiovascular disease for all adults over the age of 51 is Calcium. Calcium plays a crucial role in maintaining healthy blood pressure levels and preventing the build-up of plaque in the arteries. It also helps in muscle contractions, including the contraction of the heart muscle.
Learn more about Reducing the risk of cardiovascular disease