Calcium is the most abundant mineral in the human body and is useful in helping to maintain strong, healthy bones, teeth and nails. Calcium is essential as only 20% of an adult's bone calcium is re-absorbed each year and, as the body ages, it's ability to replace calcium decreases. This is why calcium supplements are so important, as they help to ensure you are taking on board the required daily amounts. Vitamin D is a good vitamin supplement to take alongside Calcium as it helps with absorption in the body.