As a mineral the most important function of calcium apart from aiding biological functions is skeletal mineralization. In simple words, calcium is required for building strong bones and teeth. However, its requirements change depending on the life stage you are in or on special conditions including pregnancy and lactation.
Ninety nine percent of calcium is stored in bones and teeth. The other one percent circulates in your blood and soft tissues. Calcium balance depends on the rate of bone formation and resorption. For instance, children are in positive bone balance which ensures a healthy skeletal growth, adults have already achieved peak bone mass so they are in neutral bone balance and the elderly are in negative bone balance, the reason behind age-related bone loss.
According to Clinical Journal of the American Society of Nephrology 3, dietary intake and absorption are essential to provide sufficient calcium to maintain body stores, and in turn healthy bones. It is important to note here that inadequate calcium intake results in calcium being withdrawn from bones to maintain the calcium balance, which leads to thinning and weakening of bones.
For healthy bones, having food items rich in calcium is the way to go. Good sources of calcium comprise dairy products having the highest concentration per serving of highly absorbable calcium, and dark leafy greens or dried beans having varying amounts of absorbable calcium. Non-fat and low-fat dairy products have more calcium than whole milk. Apart from natural sources, foods fortified with calcium and calcium supplements also help fulfill daily dietary calcium requirements. Certain fruit juices, cereals and breads have added calcium.
Scientific research has shown that frequent meals and oral calcium supplements promote net calcium absorption in the body. According to a research paper by Indian Council of Medical Research (ICMR), calcium supplementation can reduce the rate of bone loss and the incidence of hip fractures by 15 -50 per cent in postmenopausal women and elderly men. 

Vitamin D

Vitamin D comprises a group of fat-soluble pro-hormones, obtained from sun exposure, food, and supplements. It has to undergo chemical reactions to be converted into its active form in the body. It is needed for a host of vital functions in the body like calcium absorption, maintenance of strong bones and proper functioning of muscles, nervous system and immune system. Vitamin D is critical for bone health because it helps the intestines absorb calcium – the building block of bones.
As the primary source of vitamin D, sun exposure for 20 to 51 minutes on the face and arms is adequate for most people to produce sufficient amounts of Vitamin D. According to a research article published in Journal Nutrients, deficiency of vitamin D is a major health concern in India, in spite of the bright shining sun.
As far as daily intake of vitamin D is concerned, ICMR recommends 400 IU (10 µg) if the exposure to sunlight is minimal. Vitamin D is found naturally in foods like fatty fish, egg yolk and liver. Most people fail to get sufficient intake of Vitamin D through their diet due to limited food sources and insufficient exposure to sunlight.
According to research studies, vitamin D supplementation offers an easy, safe and inexpensive way to prevent vitamin D deficiency.

Lactose Intolerance

Lactase, an enzyme produced in the small intestine, is responsible for digesting lactose- the sugar found in milk and dairy products. In some people, a lack of this enzyme in the body leads to lactose intolerance. People with lactose intolerance cannot digest milk and other dairy products, showing symptoms such as gas, bloating, cramps and diarrhoea every time they ingest them13.
According to the journal, Advances in Nutrition 5, the principal health consequence of lactose intolerance is reduction of calcium intake brought about by poor intake of milk, resulting in reduced bone density and increased fracture risk.
There are a number of ways to meet calcium requirements if you are lactose intolerant.
Incorporate non-dairy, calcium-rich foods or lactose reduced dairy products in your diet.
Take calcium supplements
Use lactase pills or drops which help digest milk and milk products