Taking calcium through food or through supplements will serve the purpose only if you are also getting vitamin D , because Vitamin D is necessary for calcium absorption.

Vitamin D is best obtained from direct sunlight (not through windows, or sunscreen). You cannot get Vitamin D from indirect sunlight (e.g., through a window), or if you are wearing sunscreen. At least half an hour of direct sunlight per day is necessary for normal vitamin D levels.

Indian women specially the young clad now a days generally avoid sunlight in order to prevent tanning. This is a common scene on Indian roads, girls covering their face and hands with  scarf / gloves. And due to modern lifestyle a large section of office going persons do  not get enough sunlight because same is generally not available in Multi storied flats, travelling to and from office in car , spending rest of the time only indoors  in office etc. This is generally the main cause of deficiency of calcium / vitamin D

In the past we could get some Vitamin D from milk, because cows in the past contained a lot of sunlight. However, nowadays animals do not get much direct sunlight on factory farms, and so they do not make Vitamin D. Cows milk is often supplemented with vitamin D (which is manufactured from the skins of animals). Fish is also a source of this vitamin. Thus vegetarians are most susceptible  to deficiency.

Getting vitamin D from supplements can cause hypervitaminosis D which can be dangerous. The best way to get Vitamin D is through direct skin contact with sunlight, and without sunscreen. The chances of sunburn decrease with increase intakes of antioxidants (which are found in fresh fruits and vegetables).