It contain calcium which helps to make a strong bone. A cup of boiled spinach fullfil 25% of Daily requirement of calcium.
A cup of milk or a cup of yogurt are also a great source of calcium. It helps to improve bone strength.
100 gm of Papaya contains 20mg of calcium. It's helpful in increase bone strength. Also you can take it in morning for digestion.
Fish contain Omega 3 which gives good effect to whole body and also improve strength.
Banana is a good source of magensium and vitamins which is essential for bone strength. Also helpful in digestion.
Nuts contain calcium, magnesium, phosphorus, and other nutrients which is helpful for increasing bone strength.