Supplementing with vitamins and minerals is a tricky subject. The most recent scientific review recommends that healthy women NOT take calcium and vitamin D supplements to prevent bone fractures. BOTTOM LINE: No evidence for benefit, some health risk.
My recommendation for bone health: bones are like muscle mass — USE IT OR LOSE IT! Get plenty of physical activity, and even some sunshine to get your vitamin D!
This article puts the latest recommendation in context with other scientific reviews: http://www.foodpolitics.com/2013/02/supplements-advice-about-calcium-and-vitamin-d-vs-osteoporosis/
A good default principle applicable to nutrition supplementation is the precautionary principle:
“if an action or policy has a suspected risk of causing harm to the public or to the environment, in the absence of scientific consensus that the action or policy is harmful, the burden of proof that it is not harmful falls on those taking an act. This principle allows policy makers to make discretionary decisions in situations where there is the possibility of harm from taking a particular course or making a certain decision when extensive scientific knowledge on the matter is lacking. The principle implies that there is a social responsibility to protect the public from exposure to harm, when scientific investigation has found a plausible risk. These protections can be relaxed only if further scientific findings emerge that provide sound evidence that no harm will result.
In some legal systems, as in the law of the European Union, the application of the precautionary principle has been made a statutory requirement.” (Wikipedia)