The body will very kindly dispose of calcium for you as it knows it can't keep it in the blood. It will deposit it out of immediate harms way on artery walls, dump it into joint tissue or it may end up for some as part of a painful gall stone or kidney stone. Sub-optimum nutrition is the rule for most people, not the exception. It can occur simply through just not eating enough food, or as is more likely in the modern world eating a diet that is highly calorific, but nut nutrient dense. These are predominately the refined foods, alcohol and confectionery.
Some foods are rich, as in dairy produce, in specific nutrients and low in others.
A limited diet that repetitively uses the same foods is likely to be one that is unabalanced and unable to provide all the nutrients needed for health, and specifically for bone health. Sometimes, it is an excess of a particular nutrient that causes the problem in combination with low levels of other nutrients. Calcium in Balance Calcium needs a balance of phosphorous and magnesium to work effectively in building bone. Typical 'junk' food diets are rich in phosphorous which throws the balance out. Dairy produce is rich in calcium, but low in magnesium.